Download Sex and Aggregation-Sex Pheromones of Cerambycid Beetles

J Chem Ecol (2016) 42:631–654
DOI 10.1007/s10886-016-0733-8
Sex and Aggregation-Sex Pheromones of Cerambycid
Beetles: Basic Science and Practical Applications
Lawrence M. Hanks 1 & Jocelyn G. Millar 2
Received: 6 May 2016 / Revised: 25 June 2016 / Accepted: 21 July 2016 / Published online: 8 August 2016
# Springer Science+Business Media New York 2016
Abstract Research since 2004 has shown that the use of volatile attractants and pheromones is widespread in the large beetle family Cerambycidae, with pheromones now identified from
more than 100 species, and likely pheromones for many more.
The pheromones identified to date from species in the subfamilies Cerambycinae, Spondylidinae, and Lamiinae are all maleproduced aggregation-sex pheromones that attract both sexes,
whereas all known examples for species in the subfamilies
Prioninae and Lepturinae are female-produced sex pheromones
that attract only males. Here, we summarize the chemistry of
the known pheromones, and the optimal methods for their collection, analysis, and synthesis. Attraction of cerambycids to
host plant volatiles, interactions between their pheromones
and host plant volatiles, and the implications of pheromone
chemistry for invasion biology are discussed. We also describe
optimized traps, lures, and operational parameters for practical
applications of the pheromones in detection, sampling, and
management of cerambycids.
Keywords Semiochemical . Attractant . Host plant volatile .
Invasive species . Detection
Submitted to: Journal of Chemical Ecology
Electronic supplementary material The online version of this article
(doi:10.1007/s10886-016-0733-8) contains supplementary material,
which is available to authorized users.
* Lawrence M. Hanks
[email protected]
1
Department of Entomology, University of Illinois at
Urbana-Champaign, Urbana, IL 61801, USA
2
Departments of Entomology, University of California,
Riverside, CA 92521, USA
Introduction
The family Cerambycidae, or the longhorned beetles, is
among the largest insect families, with approximately 35,000
described species in the eight subfamilies currently recognized
(Švácha and Lawrence 2014). The larvae are endophytic, with
the vast majority of species developing in woody plants
(Haack 2016). As such, the beetles perform valuable ecosystem services by initiating the degradation of woody materials,
and species can be useful indicators of ecosystem health (e.g.,
Maeto et al. 2002). However, many cerambycid species are
important pests in their native regions, damaging and killing
trees in natural and managed habitats, and degrading wood
destined for lumber (e.g., Solomon 1995). The larvae frequently are long-lived, and consequently are transported readily by global commerce, concealed in wooden products and
shipping materials (Haack et al. 2010). As a result,
cerambycids are among the most common exotic phytophagous species intercepted in international quarantine (e.g.,
Brockerhoff et al. 2006; Haack 2006; Liebhold et al. 1995;
Nowak et al. 2001).
Exotic cerambycids have the potential to become devastating pests when introduced into new regions of the world. For
example, the invasion of North America, and the more recent
invasion of Europe by the Asian longhorned beetle,
Anoplophora glabripennis (Motschulsky) (Meng et al.
2015), represent examples of the invasive potential of
cerambycids, and the enormous difficulty and cost in detecting, controlling, or eradicating them from regions they have
invaded. On both continents, we are about to witness the huge
economic and environmental impact that exotic cerambycids
can have on natural and urban forests as A. glabripennis expands its ranges, attacking and killing deciduous trees of many
species (Haack et al. 2010). In the context of these and other
invasions by cerambycid beetles, pheromone-baited traps that
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are effective for detecting and sampling the insects would be
valuable additions to the otherwise meager tools available for
their surveillance, eradication, or management. This review
summarizes the rapid progress that has been made since
2004 in the identification and synthesis of cerambycid pheromones, the patterns of pheromone and host plant volatile use
by species in the various subfamilies, the development of
practical applications of their pheromones, and the implications of pheromone chemistry for invasion biology.
Types of Pheromones Used by Cerambycids
Despite the economic importance of many cerambycid species
in their native countries, and the threat they pose as potential
invaders worldwide, remarkably little is known about the basic
biology of even common and well-known species (e.g., see
Solomon 1995). Until recently, even less was known about
their chemical ecology, with attractant pheromones identified
from fewer than 10 species (Allison et al. 2004). However,
during the past decade, pheromones or likely pheromones have
been identified from more than 100 species (Tables 1, S1;
Millar and Hanks 2016). The volatile attractant pheromones
are of two types: aggregation pheromones (or aggregation-sex
pheromones, sensu Cardé 2014), that are produced by males
and attract both sexes, or sex pheromones that are produced by
females and attract only males (Millar and Hanks 2016).
Research to date suggests that the use of these two types of
pheromones breaks out along subfamily lines, with species in
the Cerambycinae, Lamiinae, and Spondylidinae using
aggregation-sex pheromones and species in the Prioninae and
Lepturinae using sex pheromones. In general, the chemistries
of the two types of pheromones are markedly different, but
within each type, there is often remarkable biosynthetic parsimony, with the same or similar pheromone components being
shared by species across genera, tribes, and in at least two
cases, different subfamilies (Tables 1, S1, discussed below).
Moreover, closely related cerambycid species on different continents often have similar, or even identical pheromones, indicating that at least some of these pheromones have persisted
unchanged for millions of years.
Sex Attractant Pheromones The first female-produced sex
attractant pheromone in the Cerambycidae was identified
from Prionus californicus Motschulsky (Prioninae) as
(3R,5S)-3,5-dimethyldodecanoic acid, given the common
name prionic acid (Rodstein et al. 2009, 2011). The pheromone is emitted in very small amounts, likely from an eversible gland on the ovipositor (Barbour et al. 2006). The pheromone is highly attractive, with lures containing submilligram
doses remaining attractive for many weeks, and attracting
male beetles from hundreds of meters away. Fortunately, the
three “non-natural” stereoisomers are not inhibitory (Rodstein
et al. 2011), so the relatively inexpensive mixture of all four
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stereoisomers can be used in lures. Although it has been possible only to show that prionic acid is present in extracts from
females of one other species (Prionus laticollis [Drury], JGM
unpub. data), the mixture of stereoisomers is attractive to
males of all six North American Prionus species with which
it has been tested, as well as the European Prionus coriarius
(L.) (Agnello et al. 2011; Barbour et al. 2011). Furthermore,
prionic acid was found to be highly attractive to males of the
Asian prionine Dorysthenes granulosus (Thomson)
(Wickham et al. 2016a), suggesting that the pheromone structure is conserved across at least these two genera. It remains to
be seen whether this compound will attract any of the many
other species of Dorysthenes that are native to Asia (Löbl and
Smetana 2010).
A second structural class of female-produced sex pheromones, consisting of 2,3-alkanediols, has been discovered in
other prionine genera (Tables 1, S1). Thus, females of several
North American species of Tragosoma seem to use various
stereoisomers of 2,3-hexanediol as sex attractant pheromones
(Ray et al. 2012a), whereas the sex pheromone of the Asian
prionine Megopis costipennis (White) consists of (2R,3S)-2,3octanediol (Wickham et al. 2016c). Surprisingly, the same 2,3alkanediol structures are used as aggregation-sex pheromones
by many species in the Cerambycinae (see below), and even
more remarkable is that the pheromone-producing prothoracic
glands seem to be similar between the female prionines and
the male cerambycines that produce these types of pheromones (see Ray et al. 2006; Wickham et al. 2016c).
Furthermore, both the chemistry of the pheromones and the
sites of production are entirely different between species that
produce prionic acid and those that produce 2,3-alkanediols
(discussed below).
Female-produced sex pheromones also have been identified from several species in the Lepturinae (Tables 1, S1). The
first such pheromone, identified from Ortholeptura valida
(LeConte), consists of cis-vaccenyl acetate. By a biological
coincidence, this chemical also is a well-known pheromone
component of male fruit flies (Drosophila species; Ray et al.
2011). Another chemical, given the common name (R)desmolactone, is a sex pheromone, or at least sex attractant
for several lepturine species in the genus Desmocerus, including the endangered D. californicus dimorphus Fisher (Ray
et al. 2012b, 2014). The authors have evidence from coupled
gas chromatography-electroantennogram detection (GCEAD) that several other lepturine species have femaleproduced sex pheromones (unpub. data), suggesting that use
of sex pheromones is common in the subfamily, but no other
structures have been identified yet.
Aggregation-Sex Pheromones To date, all volatile pheromones known from species in the Cerambycinae, Lamiinae,
and Spondylidinae are male-produced aggregation-sex pheromones (Tables 1, S1). These were the first type of pheromones
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Table 1
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Sources of cerambycid pheromone components, and references to recommended methods of synthesis
identified from cerambycids, by Iwabuchi and coworkers,
who showed that males of the Asian cerambycine
X y l o t re c h u s p y r rh o d e r u s B a t e s p r o d u c e d ( S ) - 2 hydroxyoctan-3-one and (2S,3S)-2,3-octanediol (Iwabuchi
et al. 1986; Sakai et al. 1984). The congener X. chinensis
Chevrolat subsequently was shown to produce the same two
compounds (Iwabuchi et al. 1987). Over the next 15 years,
several related structures were identified from males of other
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Table 1
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(continued)
cerambycine species, including (R)-3-hydroxyhexan-2-one,
(2R,3R)-2,3-hexanediol, and (2S,3R)-2,3-hexanediol from
the European Hylotrupes bajulus (L.), known as the old house
borer, and Pyrrhidium sanguinium (L.) (Fettköther et al. 1995;
Schröder et al. 1994); (R)-3-hydroxyhexan-2-one and (R)-3hydroxyoctan-2-one from the Asian Anaglyptus subfasciatus
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Table 1
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(continued)
Pic (Leal et al. 1995); and (S)-2-hydroxydecan-3-one and 3hydroxydecan-2-one from the Asian Xylotrechus quadripes
Chevrolat (Jayarama et al. 1998; Rhainds et al. 2001).
The use of these closely related structures by species in
different genera and tribes, and from different continents, suggested that the hydroxyketone and 2,3-alkanediol type pheromones were highly conserved within the subfamily, and this
has since been borne out by the identification of these types of
structures as pheromones or likely pheromones for numerous
cerambycine species from different regions of the world
(Table S1). The corresponding 2,3-alkanediones are found
frequently in headspace volatiles from male beetles, but to
date, it seems likely that they are artifacts, because there is
no evidence that they are attractants or synergists. In addition,
the first variations on the hydroxyketone motif recently have
been discovered, such as (2S,4E)-2-hydroxyoct-4-en-3-one
and (3R,4E)-3-hydroxyoct-4-en-2-one, which were discovered from Tylonotus bimaculatus Haldeman (Zou et al.
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2015), i.e., unsaturated analogs of hydroxyoctanone. The first
examples of acetylated hydroxyketone structures also have
been tentatively identified from cerambycine species (JGM,
unpub. data).
In addition to the hydroxyketone and 2,3-alkanediol type
pheromones, evidence is accumulating that the pheromones
of cerambycine species actually may be very diverse
(Table S1). For example, very small and simple molecules
such as 1-butanol and the enantiomers of 2-methylbutanol
have been identified from several different species. Other
species such as Megacyllene caryae (Gahan) have pheromones consisting of terpenoids such as geranial and neral
(Lacey et al. 2008), whereas Rosalia funebris Motschulsky
produces (Z)-3-decenyl (E)-2-hexenoate (Ray et al. 2009a),
which resembles compounds from true bugs. Recently, the
novel pyrrole structure 1-(1H-pyrrol-2-yl)-1,2-propanedione
was found in the headspace volatiles from male beetles in
several different cerambycid genera, either alone or in combination with 3-hydroxyhexan-2-one (Table S1; JGM, LMH,
and coworkers, unpub. data), and in field trials, it has proven
to be a crucial component of attractant blends for at least
two invasive Callidiellum species from Asia, C. rufipenne
(Motschulsky) (Zou et al. 2016) and C. villosulum
(Fairmaire) (Wickham et al. 2016b). Other recently identified pheromones or likely pheromones include the unsaturated straight-chain aldehyde (6E,8Z)-6,8-pentadecadienal
(Silva et al. 2016a) and the saturated methyl-branched aldehyde 10-methyldodecanal (Silva et al. 2016b), as well as a
pyrone, a tetrahydropyran, and several cyclic terpenoid derivatives (JGM, LMH, and coworkers, unpub. data). Thus, it
seems that cerambycine pheromones may be characterized
by widely divergent structural types, but with widespread
sharing of particular structural types among more closely
related species.
In contrast, the known or suspected pheromones of species
in the Lamiinae fall into two main structural classes. The first
class consists of geranylacetone; the corresponding alcohol
(E)-6,10-dimethylundeca-5,9-dien-2-ol (known as fuscumol);
and its acetate ester (E)-6,10-dimethylundeca-5,9-dien-2-yl
acetate (fuscumol acetate), either as single components or as
blends (Table S1). The latter two components each have two
enantiomeric forms, providing additional opportunities for
evolution of species-specific blends. For example, a recent
study found evidence in North American lamiines of the relatively rare phenomenon of enantiomeric synergism (Meier
et al. 2016): males of Astylidius parvus (LeConte) produce
(R)- and (S)-fuscumol + (R)-fuscumol acetate +
geranylacetone, whereas males of Lepturges angulatus
(LeConte) produce (R)- and (S)-fuscumol acetate +
geranylacetone. The fact that several other lamiine species
are known to produce nonracemic blends of fuscumol enantiomers (LMH, unpub. Data) suggests that enantiomeric synergism may be common within this subfamily.
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The second class of pheromone structures found from
lamiine species consists of hydroxyethers and related compounds. The first example, a blend of 4-(heptyloxy)butan-1ol and the corresponding aldehyde, was identified from the
notoriously invasive A. glabripennis (Zhang et al. 2002).
The alcohol component has now been identified from the
Asian congener Anoplophora chinensis (Forster) as well
(Hansen et al. 2015). A related pheromone, 2-(undecyloxy)
ethanol (known as monochamol) was identified originally
from the European Monochamus galloprovincialis Olivier
(Pajares et al. 2010), and has since been shown to be a pheromone or likely pheromone for another 13 congeners native to
Eurasia and North America (Table S1). Furthermore, during
field bioassays in China, monochamol was found to attract
species in four other lamiine genera (Acalolepta formosana
[Breuning], Pharsalia subgemmata [Thomson],
Pseudomacrochenus antennatus [Gahan], and Xenohammus
bimaculatus Schwarzer; Wickham et al. 2014), suggesting
that it represents another highly conserved pheromone motif.
However, the African Monochamus leuconotus (Pascoe)
seems to be an exception, because the males produce a different hydroxyether, 2-(heptyloxybutoxy)ethanol (Hall et al.
2006; Pajares et al. 2010). It remains to be seen what other
pheromone structures will be found from species in the
Lamiinae, and whether they will be as diverse as those turning
up among species in the Cerambycinae.
To date, all known or suspected pheromones from species
in the Spondylidinae are of the geranylacetone structural class
shared with some lamiines (Table S1). In fact, fuscumol was
first identified from the Palearctic spondylidine Tetropium
fuscum (F.) and the North American T. c. cinnamopterum
Kirby (Silk et al. 2007; Sweeney et al. 2010). Fuscumol has
since been implicated as a pheromone for several other
spondylidine species (Table S1). Overall, pheromones or likely pheromones have been identified from only a few species of
this relatively small subfamily (see Švácha and Lawrence
2014), and so it is impossible to predict whether this subfamily
will turn out to have a diversity of pheromone structures.
No pheromones have been identified from species in the
remaining three currently recognized subfamilies in the
Cerambycidae — the Parandrinae, Necydalinae, and
Dorcasominae — all of which are relatively small (Švácha
and Lawrence 2014).
Conundrums among the Volatile Pheromones of
Cerambycidae Over the past decade of studying cerambycid
pheromones, the authors and their coworkers have encountered several examples of two currently unexplainable phenomena. First, males of several cerambycine species produce
chemicals that are typical pheromone components of
cerambycines, but all attempts at attracting the producing species with these compounds have failed. For example, males of
the sugar maple pest Glycobius speciosus (Say) and the
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important outbreak pest Enaphalodes rufulus (Haldeman)
both produce two isomers of 2,3-hexanediol, but all attempts
to attract beetles with racemic or chiral compounds, emitted
singly or as blends, in traps placed at ground level or in the
forest canopy, have failed. Males of Tragidion armatum
Linsley produce copious quantities of (R)-3-hydroxyhexan2-one, but no beetles have been attracted to traps by lures
containing either the chiral or racemic compound. Finally,
males of the very common and abundant locust borer,
Megacyllene robiniae (Forster), produce an isomer of 2,3hexanediol, (R)-3-hydroxyhexan-2-one, and (R)-1phenylethan-2-ol, but attempts to trap beetles with all possible
blends of components, over trials spanning a decade, have
provided no evidence of even the slightest attraction. In all
four cases, the compounds are produced sex specifically by
males, and their structures are identical to common pheromone components of related species, so it seems unlikely that
the compounds might be, for example, defensive compounds
instead of pheromones.
Conversely, large numbers of both sexes of the invasive
species Callidiellum rufipenne were serendipitously attracted
to a blend of 3-hydroxyhexan-2-one and 1-(1H-pyrrol-2-yl)1,2-propanedione during a field trial in Japan that targeted a
different species (Zou et al. 2016). Although we have found 3hydroxyhexan-2-one in numerous extracts of headspace volatiles from male C. rufipenne, we have never detected the
pyrrole in any extracts (Zou et al. 2016). Furthermore, 3hydroxyhexan-2-one alone is not attractive. Thus, it is unclear
why both compounds are necessary for attraction of this species when all analyses done to date indicate that the males
produce only one of the two components. However, it does
suggest that it may be worth field testing the pyrrole as a
possible “cryptic” pheromone component for the three currently intractable species described in the previous paragraph.
Morphological Structures and Behaviors Associated with
Pheromone Use To date, two types of pheromone-producing
structures have been identified in various cerambycid species:
glands in the prothorax, or glands associated with the ovipositor (Millar and Hanks 2016). Prothoracic glands are common
in many species of cerambycines that produce pheromones of
the hydroxyalkanone-alkanediol motif, such as Xylotrechus
pyrrhoderus (Iwabuchi 1986), Anaglyptus subfasciatus
(Nakamuta et al. 1994), Hylotrupes bajulus (Noldt et al.
1995), and Neoclytus a. acuminatus (F.) (Lacey et al.
2007b). Nevertheless, some cerambycines that have the
male-specific prothoracic pores have aggregation-sex pheromones with different structures. For example, males of
Tylonotus bimaculatus have prominent pores which are absent
in females (LMH, unpub. data), and produce a blend of
(2S,4E)-2-hydroxyoct-4-en-3-one with smaller amounts of
three isomers. This compound is an unsaturated analog of 2hydroxyoctan-3-one, and so does not represent a significant
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departure from the hydroxyalkanone-alkanediol motif.
However, Chlorida festiva (L.) also has the male-specific
pores (Ray et al. 2006), but males produce a pheromone of
very different structure, (6E,8Z)-6,8-pentadecadienal (Silva
et al. 2016a).
The pheromone glands of cerambycines are in the
endocuticle of the prothorax, and connect by ducts to pores
on the cuticular surface (Hoshino et al. 2015). The fact that
the prothoracic gland pores are sex specific in cerambycines
suggests that they can be used as reliable evidence that a species uses an aggregation-sex pheromone. For example, in a
morphological study of cerambycine species, Ray et al.
(2006) reported that 49 of the 65 species had the malespecific pores, and indeed, 11 of those species subsequently
were found to use aggregation-sex pheromones (Lacey et al.
2008, 2009; Mitchell et al. 2013, 2015; Ray et al. 2015; Zou
et al. 2016). In contrast, the absence of male-specific gland
pores may indicate either that a species does not use a volatile
pheromone, or that the pheromone glands are elsewhere on the
body. For example, the cerambycine Rosalia funebris lacks the
male-specific gland pores (Ray et al. 2006), and males produce
a pheromone with a unique structure ([Z]-3-decenyl [E]-2hexenoate), from as yet unidentified glands (Ray et al. 2009a).
Prothoracic gland pores also have been associated with production of female-produced sex pheromones in some species in
the Prioninae, with the pores being specific to females.
Remarkably, the 2,3-alkanediols used as sex pheromones in
these prionine species are the same compounds as are produced
by males of many cerambycine species (Table S1). For example, females of the North American Tragosoma depsarium “sp.
nov. Laplante” (tribe Meroscelisini) have prothoracic gland
pores, and they produce (2R,3R)-2,3-hexanediol as a sex pheromone that attracts only males (Ray et al. 2012a). Similarly,
females of the Asian prionine Nepiodes (formerly Megopis) c.
costipennis White (tribe Megopidini) have prothoracic gland
pores and produce (2R,3S)-2,3-octanediol as a sex pheromone
(Wickham et al. 2016c).
Another group of species in the Prioninae uses sex pheromones that apparently are produced by an eversible gland on
the ovipositor. In female Prionus californicus, extracts of this
gland contained prionic acid, as well as several analogs and
homologs, although prionic acid alone is both necessary and
sufficient for attraction of males (Maki et al. 2011b; Rodstein
et al. 2009, 2011).
There is little information about biosynthesis of
cerambycid pheromones. Kiyota et al. (2009) reasoned
that the structural similarity between the (S)-2hydroxyoctan-3-one and (2S,3S)-2,3-octanediol pheromone components of Xylotrechus pyrrhoderus indicated
that one was the biosynthetic precursor of the other.
They tested this hypothesis by synthesizing deuteriumlabeled standards of each compound, topically applied
them to the prothoraces of males, and subsequently
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collected the chemicals that males produced. This study
demonstrated that the ketol was converted to the diol,
pinpointing the ketol as the precursor (also see Iwabuchi
et al. 2014).
For the Spondylidinae, Mayo et al. (2013) suspected that
geranylacetone was a biosynthetic precursor of fuscumol for
male Tetropium fuscum based on its structural relationship and
presence as a minor component in headspace aerations. This
was confirmed by topically applying deuterium-labeled
geranylacetone to males, resulting in them producing labeled
fuscumol. A suspected key biosynthetic enzyme was
expressed primarily in the midgut, suggesting that the pheromone was produced there. Zarbin et al. (2013) also applied
labeled geranylacetone to different body parts of males of the
lamiine Hedypathes betulinus (Klug), demonstrating that the
chemical was converted to labeled fuscumol and fuscumol
acetate by tissues in the prothorax of males, but there was no
such effect in females.
Calling behaviors of cerambycids vary with the type of
pheromone they produce and the location of their pheromone
glands. Males of cerambycines that have the prothoracic gland
pores commonly adopt a characteristic “push-up stance” that is
thought to aid in dissemination of pheromone: the front legs are
extended, elevating the prothorax above the substrate (Lacey
et al. 2007a, b, 2009; Ray et al. 2009b). Males of the
spondylidine Tetropium fuscum display a similar behavior that
is associated with release of the aggregation-sex pheromone
fuscumol (Lemay et al. 2010), although the location of the
pheromone glands has not yet been verified (Mayo et al. 2013).
Female Prionus californicus adopt a very different posture
when calling, with the head down, the tip of the abdomen
raised, and the ovipositor extended (Barbour et al. 2006).
The presumed pheromone gland, on the dorsum of the ovipositor, then is everted. Additional reports of similar postures
in female prionines of other species (e.g., Benham and Farrar
1976; Gwynne and Hostetler 1978; Paschen et al. 2012), is
further evidence that use of sex pheromones is likely widespread among the prionines, and that pheromones are produced by a gland on the ovipositor.
The antennae have been demonstrated to be the organs that
cerambycids use to perceive volatile pheromones. The sexually dimorphic, more heavily branched antennae of prionine
males suggested that they use sex pheromones to find females
(Linsley 1959), in analogy to male Lepidoptera. The role of
the antennae as pheromone detectors has been supported by
several studies using electroantennography (e.g., Álvarez et al.
2015a; Iwabuchi et al. 1985; MacKay et al. 2015; Ray et al.
2011; Rodstein et al. 2009). To our knowledge, the molecular
basis of pheromone reception has been explored only once to
date, by Mitchell et al. (2012), who functionally characterized
olfactory receptors for three of the nine pheromone components produced by males of the cerambycine Megacyllene
caryae. Two of the receptors also were sensitive to isomers
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that are pheromone components of other cerambycine species,
consistent with the important role of antagonism by components in the pheromone blends of sympatric congeners in
averting interspecies attraction (e.g., Mitchell et al. 2015).
Nonvolatile Contact Pheromones Once the sexes are in contact, male cerambycids recognize females by contact chemoreception, detecting species- and sex-specific contact pheromones in the cuticular wax layer of females (Hanks and
Wang 2016). Several of these contact pheromones have been
identified, and they consist of a subset of the cuticular lipids
that make up the wax layer (reviewed by Ginzel 2010; Millar
and Hanks 2016). Moreover, there is now evidence from several cerambycid species that non-volatile chemicals (possibly
lipids) that females deposit on the substrate while walking may
act as a chemical trail that males can follow to locate females
(Galford 1977; Hoover et al. 2014; Wang 1998, 2002).
Implications of Pheromone Chemistry for Invasion
Biology
The cumulative body of research on cerambycid chemical
ecology has shown that the pheromone chemistry of related
species often is highly conserved, with many species sharing
pheromone components, or even having identical pheromones
(Table S1). Moreover, pheromone components may be shared
by species on different continents, despite their having diverged many thousands of years ago, notably: 1)
hydroxyalkanones and alkanediols among cerambycines; 2)
fuscumol, fuscumol acetate, and monochamol among
lamiines; 3) fuscumol among spondylidines; and 4) prionic
acid and alkanediols among prionines (Table S1). These close
similarities in pheromone composition are supported further
by the recently discovered 1-(1H-pyrrol-2-yl)-1,2propanedione, which is at least an attractant or synergist for
five species of Asian cerambycines (Wickham et al. 2016b;
Zou et al. 2016), and a confirmed pheromone component of
the North American cerambycine Dryobius sexnotatus
Linsley (LMH, unpub. data).
This pheromonal parsimony among cerambycids in different parts of the world has profound implications for the successful colonization of exotic species. Specifically, new populations of invaders usually will be founded by a small number of adults emerging from wood products or wooden packing materials. Asynchronous emergence of adults will result in
their being widely separated as they disperse into the new
region. The dispersion of these few founding adults will be
even greater for lamiine species, because adults require a period of maturation feeding before mating. Thus, initial population densities will be very low and it will be difficult for
males and females to find one another to mate, the so-called
Allee effect (Courchamp et al. 1999). Under these conditions,
pheromonal communication for the invading species may be
J Chem Ecol (2016) 42:631–654
significantly disrupted by calling adults of much more abundant native species that use the same pheromone components,
posing a major barrier to reproduction and establishment.
Thus, at least some exotic cerambycid species may fail to
establish because their pheromone channel overlaps with
those of native species. Conversely, the exotic species that
have the best chance of establishing may be those whose
pheromone chemistries do not overlap with those of any native species, allowing for efficient and unhindered mate location. In short, the latter species are able to colonize and invade
a “pheromone-free space”. It should be noted that the concept
of pheromone-free space is by no means exclusive to
cerambycids, but likely applies to any invasive insect species
that relies on volatile pheromones to bring the sexes together.
An example of a successful invader that may have benefited from pheromone-free space is Asian longhorned beetle, the
highly polyphagous Asian longhorned borer, Anoplophora
glabripennis (Haack et al. 2010). The two-component aggregation-sex pheromone of this species seems to be unique in
North America, based on two lines of evidence (Table S1): 1)
no native species has yet been found to produce either compound, and 2) no native species have been shown to be significantly attracted by the synthesized pheromones during
trapping programs conducted in multiple areas of the eastern
USA, and for extended periods of time (DiGirolomo and
Dodds 2014; Nehme et al. 2014; unpub. data). Thus, establishment of A. glabripennis may have been favored by its
having a unique pheromone, allowing it to independently colonize multiple regions of North America (Haack et al. 2010).
In contrast, the European Tetropium fuscum has established
in Canada, despite the fact that it uses the same pheromone,
fuscumol, as is used by several native spondylidines, including
T. c. cinnamopterum. Moreover, it seems that many North
American lamiine species share fuscumol as a pheromone component (Table S1). This overlap in pheromone chemistry may
explain why the invasion of North America by T. fuscum has
stalled, with minimal spread during the 20 years since its introduction, possibly due to low population densities and reproductive failure (Dearborn et al. 2016; Rhainds et al. 2011). It seems
possible, and even likely that the geographic range of this invader has been constrained by interference in its pheromone
communication by the much more abundant native
spondylidines and lamiines that use the same pheromone.
Collection, Analysis, and Identification of Cerambycid
Pheromones
The methods used to identify volatile pheromones of
cerambycids depend on the amounts available, which in turn
depend to a large extent on the type of pheromone being
produced. Specifically, aggregation-sex pheromones generally are produced in microgram or larger amounts, i.e., amounts
that are sufficient to obtain NMR spectra. In optimal cases, it
639
has proven possible to simply concentrate and replace the
methylene chloride in the extract containing headspace volatiles with deuterated methylene chloride, and run the resulting
concentrated extract with microprobe NMR (e.g., Silva et al.
2016a, b). In contrast, female-produced sex pheromones seem
to be produced in only nanogram amounts per individual, so
all identifications to date have relied on combinations of mass
spectral interpretations, microchemical tests, and use of retention indices, because the amounts available were not sufficient
for NMR analysis. Below, we describe the methods used to
obtain crude pheromone extracts, followed by the specific
conditions used for analyses of those extracts.
Pheromone Collection Methods The first cerambycid pheromones identified, the aggregation-sex pheromones of
Xylotrechus pyrrhoderus and X. chinensis, were collected by
confining beetles in glass containers and then rinsing the containers with solvent, or by extracting whole insects or body
parts with solvent (Iwabuchi 1986; Iwabuchi et al. 1987;
Kuwahara et al. 1987; Sakai et al. 1984). These methods also
were used during identification of the pheromone of
Hylotrupes bajulus (Fettköther et al. 1995). Crude extracts
of most other cerambycid pheromones have been obtained
by what has become the standard methodology for collecting
odor samples, that is, by passing clean air through a closed
chamber containing the insects (with or without host plant
material), and trapping the headspace volatiles on an adsorbent such as Tenax (Supelco, Bellefonte, PA, USA), Porapak
Q (now Hayesep Q; Sigma-Aldrich, St. Louis, MO, USA), or
activated charcoal (Millar and Simms 1998). The trapped volatiles then are eluted with small volumes of a solvent such as
methylene chloride. For the aggregation-sex pheromones, aeration samples of a single beetle, if the beetle has produced
pheromone at all, usually are dominated by the maleproduced compound(s), so that they are unmistakable, even
if the beetle is aerated along with host plant material.
In contrast, aeration extracts from species with femaleproduced sex pheromones usually are entirely different, with
the pheromone peak being a minor or trace component. Thus,
careful comparison of extracts with the corresponding controls,
with the analogous extracts from male beetles, or both, is required to locate pheromone candidates. This process is made
much more reliable and efficient if the extracts are analyzed by
coupled gas chromatography-electroantennography (GCEAD), because the antennae of males respond strongly and
selectively to even trace amounts of the pheromone components (e.g., Ray et al. 2011, 2012b, 2014). In the case of
Prionus californicus, collections of headspace odors from females did not contain enough material to elicit a detectable GC
peak. Instead, a composite sample was finally obtained by
inserting a solid phase microextraction fiber into the opening
from which the presumed pheromone gland was everted, on the
ovipositors of 14 females, followed by thermal desorption of
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the entire sample directly into the GC column (Rodstein et al.
2009). This method produced a sample with detectable peaks,
from which mass spectra were obtained (Rodstein et al. 2009).
The identification of the pheromone of P. californicus was particularly difficult because of the high polarity and poor chromatographic properties of the critical compound, the carboxylic
acid 3,5-dimethyldodecanoic acid (Rodstein et al. 2009).
Analysis of Cerambycid Pheromone Components GCEAD, to detect potential pheromone compounds, and coupled
gas chromatography-mass spectrometry (GC-MS), to provide
mass spectra and retention indices, are typically the methods
used to analyze extracts of insect pheromones, because of the
excellent resolution of GC, and the nanogram or less sensitivity of both methods. However, there are two potential pitfalls.
First, some cerambycid pheromone components, such as 2methylbutan-1-ol, are very volatile, and so the GC temperature program must have a low initial temperature to ensure that
they are not missed, or hidden under the solvent peak.
Alternatively, the presence of a very volatile compound can
be verified by a solventless collection method, such as solid
phase microextraction.
Second, the most common types of cerambycine pheromones, the 3-hydroxyalkan-2-ones and the corresponding 2hydroxyalkan-3-ones, are thermally labile and readily interconvert between the two regioisomers in hot GC injector ports
or columns (Leal et al. 1995; Sakai et al. 1984). Thus, for
analyses of these types of compounds, it is essential to use a
relatively low injector temperature (e.g., 100 °C), particularly
when running samples in splitless mode where the dwell time
of the sample in the injector is many seconds. Alternatively,
cool on-column injection (e.g., Rhainds et al. 2001), or programmed temperature vaporization can be used for sample
introduction. In parallel, a slow oven temperature program
helps to minimize isomerization.
Some cerambycid pheromones, such as the hydroxyether
compounds produced by species of Monochamus and
Anoplophora, are achiral and do not have stereoisomers, and
so can be completely identified on the basis of GC retention
time and mass spectral matches with standards. However, other types of pheromones may have positional and/or stereoisomers, and so several sequential analyses are required to fully
identify the structure, as follows:
1. The enantiomers of 2-methylbutan-1-ol are resolved on a
chiral stationary phase Cyclodex B column (J&W
Scientific, Folsom, CA, USA), with the (R)-enantiomer
eluting first (e.g., Hanks et al. 2007). They also resolve
on a Betadex 225 column (J&W Scientific).
2. The positional isomers 2-hydroxyhexan-3-one and 3hydroxyhexan-2-one do not separate well on a nonpolar
DB-5 column (J&W Scientific), but they can be distinguished by their mass spectra. Alternatively, all four of the
J Chem Ecol (2016) 42:631–654
isomers (i.e., the pairs of enantiomers of each positional
isomer) are readily separable on either a Cyclodex B column (elution order 2R:3R:2S:3S) or a Betadex 225 column (retention order 3R:2R:2S:3S). Remarkably, the enantiomers of 3-hydroxyhexan-2-one are separated by several minutes on a Mega-Dex DAC-Beta column (Mega
SNC, Legnano, Italy; Andres Gonzalez, pers. comm.). If a
chiral stationary phase column is not available, the
hydroxyketones can be esterified with (R)- or (S)methoxy(trifluoromethyl)phenyl acetyl chloride to form
diastereomeric derivatives that are separable on a standard
GC column (e.g., Leal et al. 1995).
For the corresponding eight-carbon analogs, the positional
isomers again do not separate well on a nonpolar DB-5 column, but are completely separated on a polar DB-Wax column, with the 2-hydroxyoctan-3-one eluting first. On a
Cyclodex B column, the elution order is 2R:2S:3R:3S, but
the 2S and 3R-stereoisomers nearly overlap. However, by sequential analysis on DB-Wax to determine which positional
isomer is present, followed by analysis on Cyclodex B, each
isomer can be identified unequivocally.
Similarly, the positional isomers of the 10-carbon homologs are not well resolved on a DB-5 column, but they are
easily separable on polar GC phases, or they can be readily
identified from their mass spectra. The enantiomers of 2hydroxydecan-3-one resolve on a Cyclodex B column (2R
elutes first; Rhainds et al. 2001), or on a CP-Chirasil-DexCB
column (2R elutes first; Chrompack, Middleberg,
The Netherlands; Hall et al. 2006). Similarly, racemic 3hydroxydecan-2-one resolves on Cyclodex B, but we have
not yet made enantiomerically enriched standards to determine which peak corresponds to which enantiomer.
3. The stereoisomers of 2,3-hexanediol and 2,3-octanediol
are identified readily in two steps. First, the syn- and antidiastereomers of the 2,3-alkanediols are well separated on
DB-5 and DB-17 columns, or on polar phases (e.g.,
Fettköther et al. 1995), with the syn-diastereomers eluting
first. Second, all four stereoisomers of each compound
separate well on Cyclodex B (elution order for
hexanediols and octanediols: 2S,3S: 2R,3R: 2R,3S:
2S,3R). The syn-enantiomers also resolve well on a βcyclodextrin column (SGE, Milton Keynes, UK), with
the (2S,3S)-enantiomer eluting first (Hall et al. 2006).
4. The E- and Z-isomers of fuscumol are readily separable
by GC; so far, only the E-isomer has been reported as a
cerambycid pheromone (Table S1). Fuscumol is not resolved on Cyclodex B or Betadex 225 columns, and is
only partially resolved on permethylated cyclodextrin columns (HP-Chiral 20B, Agilent, Santa Clara, CA, USA,
Vidal et al. 2010; or β-Dex 120, Supelco, Sweeney et al.
2010). Fuscumol acetate is resolved on Cyclodex B, and
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partially resolved on HP-Chiral-20B (Vidal et al. 2010).
Alternatively, fuscumol can be derivatized with
enantiomerically pure (R)- or (S)-2-acetoxypropionyl
chloride (Slessor et al. 1985). The resulting diastereomeric derivatives separate easily on a standard GC column
(e.g., Meier et al. 2016; Sweeney et al. 2010).
5. The enantiomers of desmolactone are not resolved
on Cyclodex B, but do resolve on β-Dex 225
(Ray et al. 2012b).
6. Prionic acid (3,5-dimethyldodecanoic acid) has four stereoisomers (two diastereomeric pairs of enantiomers).
The syn- and anti-diastereomers separate easily on a nonpolar DB-5 column, with syn eluting first. The corresponding methyl esters elute in the same order, with the
added advantage that the peak shapes are better, and the
retention times are more reproducible than those of the
free acids. However, neither of the enantiomeric pairs of
methyl esters was resolvable on a Cyclodex B chiral stationary phase column. Thus, the insect-produced enantiomer had to be deduced from bioassays of the two anti
enantiomers (i.e., 3R,5S and 3S,5R; Rodstein et al. 2011).
Synthesis of Cerambycid Pheromones
Table 1 lists all cerambycid pheromones reported to date,
where they can be obtained, and/or their recommended
methods of synthesis, with the exception of some minor components such as 2-nonanone and some monoterpenes that are
readily available from numerous commercial sources. Some
further discussion on the syntheses of several of these compounds is warranted. In particular, for practical applications,
syntheses of the aggregation-sex pheromones must yield
multigram and even kilogram quantities because lures must
contain 25–100 mg or more of pheromone components to
allow release of several milligrams per day for periods of a
few weeks. Thus, syntheses must be short, efficient, and if
possible, involve no expensive chromatographic purifications
of intermediates or final products.
1. Racemic and (S)-2-methylbutan-1-ol are readily available, but the (R)-enantiomer apparently is not. In our experience, smaller companies purporting to sell the (R)enantiomer actually provided either the (S)-enantiomer
or the racemate, i.e., caveat emptor. However, the (R)enantiomer is readily available by enzymatic resolution
of the racemate (Bello et al. 2015), or it can be made from
commercial (S)-3-bromo-2-methylpropan-1-ol (Mitchell
et al. 2012).
2. 2,3-Hexanedione and the corresponding 8- and 10-carbon
analogs are seen frequently in aeration extracts of species
that produce 2-hydroxyalkan-3-ones or 3-hydroxyalkan-2ones, but to date, have not been shown to be active for any
641
species. Nevertheless, 2,3-hexanedione is commercially
available, and analytical standards of the 8- and 10carbon compounds are readily made by oxidation of the
corresponding hydroxyketones (e.g., Hall et al. 2006) or
permanganate oxidation of 2-alkenes (Rhainds et al. 2001).
3. The hydroxyketone pheromones have been prepared as a
mixture of all four stereo- and regioisomers by partial
reduction of 2,3-alkanediones using NaBH4 in ethanol
(Hanks et al. 2007), or more cleanly by reduction with
zinc and ZnCl 2 (Millar et al. 2009). Racemic 3hydroxyalkan-2-ones can be prepared by reaction of the
lithium anion of 2-methyl-1,3-dithiane with the appropriate aldehydes, followed by deprotection (Fettköther et al.
1995; Schröder et al. 1994), or by alkylation of
trimethylsilyl-protected cyanohydrins with methyllithium
followed by hydrolysis of the imine intermediates
(Rhainds et al. 2001). However, the recommended route
is the one-pot reaction of 3-hydroxy-1-alkynes with BF3
in MeOH with HgO catalyst, followed by aqueous acidic
hydrolysis of the intermediate methyl enol (Imrei et al.
2013; Leal et al. 1995). The reaction also can be done in
one step using aqueous H2SO4, but larger amounts of the
highly toxic HgO catalyst apparently are required
(Noseworthy et al. 2012). This reaction uses relatively
inexpensive and readily available intermediates, is easily
scalable to >100-g quantities; and when reaction conditions are optimized, yields are good to excellent.
Enantiomerically enriched 3-hydroxyalkan-2-ones
have been prepared by Wacker oxidation of OHprotected chiral 1-alken-3-ols (Schröder et al. 1994), or
by ring-opening of protected epoxyalcohols and oxidation, with the epoxyalcohol intermediates being generated
from kinetic resolution of allylic alcohols by Sharpless
asymmetric epoxidation (Leal et al. 1995). Alternatively,
HgO-catalyzed reaction of chiral 1-alkyn-3-ol substrates,
as described above, produces the desired hydroxyketones
without epimerization (Leal et al. 1995). However, the
simplest and recommended route to both enantiomers is
by kinetic resolution of the racemate with Amano lipase
AK and vinyl acetate, resulting in highly selective acetylation of the (S)-enantiomer. The unchanged (R)-3hydroxyalkanone and the acetylated (S)-enantiomer are
separated easily on multigram scale chromatographically
(Lacey et al. 2007a). The (S)-enantiomer is recovered by
careful alkaline hydrolysis, to minimize epimerization.
Alternatively, racemic 3-O-acetylalkan-2-one can be
enantioselectively hydrolyzed with the same enzyme in
neutral phosphate buffer to produce the (S)-3hydroxyalkan-2-one (Lacey et al. 2007a).
Racemic 2-hydroxyalkan-3-ones can be made by reaction
of 2-alkyl-1,3-dithianes with acetaldehyde (Fettköther et al.
1995; Schröder et al. 1994), or reaction of the trimethylsilyl-
642
protected cyanohydrin from acetaldehyde with alkyllithiums
(Rhainds et al. 2001). However, syntheses of the racemates are
probably unnecessary because of the ease with which the enantiomers can be prepared (see below). The enantiomers of 2hydroxyalkan-3-ones have been synthesized by kinetic resolution of allylic alkenols to chiral epoxides followed by ring
opening and oxidation (Mori and Otsuka 1985; Rhainds et al.
2001). However, the simplest and cheapest method for synthesis of 2-hydroxyalkan-3-ones is via alkylation of the lithium salts of tetrahydropyran-protected lactic acid enantiomers,
a total of four straightforward steps from commercially available (R)- or (S)-ethyl lactates (Hall et al. 2006; Lacey et al.
2008; Sakai et al. 1984). The tetrahydropyran protecting
group was found to be best when compared to benzyl or silyl
protecting groups (Hall et al. 2006).
4. Mixtures of all four stereoisomers of 2,3-alkanediols can
be made by NaBH4 reduction of the corresponding 2,3alkanediones (Hanks et al. 2007) or LiAlH4 or NaBH4
reduction of racemic 2-hydroxyalkan-3-ones or 3hydroxyalkan-2-ones (Fettköther et al. 1995; Lacey
et al. 2008). The racemates of the syn- and anti-diastereomers can be prepared in large scale and with good yield in
one step by OsO4-catalyzed oxidation of the corresponding (E)- or (Z)-2-alkenes, respectively, with inexpensive
N-methylmorpholine N-oxide as the terminal oxidant
(Lacey et al. 2004).
The individual stereoisomers of 2,3-alkanediols can be
prepared in several ways. Historically, several multistep
routes were developed based on chiral starting materials
(Sakai et al. 1984; Schröder et al. 1994) or the Sharpless
asymmetric epoxidation (Mori and Otsuka 1985;
Schr öde r et a l. 1 994 ) . Sha r pl e s s a s ym m e t r i c
dihydroxylation of stereochemically pure 2-alkenes also
has been used to provide a one-step synthesis, but the
resulting diols are only ~80–90 % enantiomerically pure
(Hall et al. 2006; Lacey et al. 2004). Alternatively, reduction of enantiomerically enriched starting hydroxyketones
produces a chromatographically separable mixture of the
corresponding syn- and anti-diols (e.g., [R]-3hydroxyhexan-2-one produces a mixture of [2R,3R]- and
[2S,3R]-2,3-hexanediols; Hall et al. 2006; Lacey et al.
2008). For multigram scale, kinetic resolution of the racemic anti-diols with Amano lipase PS and vinyl acetate in
methyl t-butyl ether is the preferred method, with the
(2R,3S)-enantiomer being selectively acetylated
(Wickham et al. 2016c). In contrast, the enantiomers of
syn-2,3-alkanediols can be prepared in a few steps in
multigram amounts from commercially available D- or
L-threonine (Mitchell et al. 2012).
5. The enantiomers of fuscumol and fuscumol acetate are
prepared easily in multigram scale by kinetic resolution
of racemic fuscumol with an immobilized lipase
J Chem Ecol (2016) 42:631–654
(Novozyme 435) from the yeast Pseudozyma
(=Candida) antarctica (Goto, Sugiy. & Iizuka)
Boekhout (Sigma-Aldrich; Hughes et al. 2013; Sweeney
et al. 2010; Vidal et al. 2010). Choice of the lipase was
important, because other lipases produced much poorer
resolution (Sweeney et al. 2010).
6. All of the hydroxyether-type pheromones (e.g.,
monochamol) are readily prepared by standard
Williamson ether syntheses, reacting an alkoxide with
an alkyl halide (e.g., Zhang et al. 2002).
Only single syntheses of most of the other pheromones
shown in Table 1 have been reported, and the citations to
those syntheses are listed in the table.
Host Plant Volatiles and Bark Beetle Pheromones
as Kairomones
Many cerambycid beetles mate on the host plants on which the
adults feed, or on the host plants of the larvae, suggesting to
Linsley (1959) that finding mates and finding host plants are
intimately associated. It had long been suspected that the adult
beetles primarily use volatile cues to locate host plants (e.g.,
Beeson 1930), which encouraged some authors to conclude
that various species did not use long-range attractant pheromones (e.g., Allison et al. 2004; Hanks et al. 1996; Lu et al.
2007). Much of the research on attraction of cerambycids by
plant volatiles has focused on species whose larvae develop in
coniferous trees that have been stressed by environmental conditions (e.g., Fan et al. 2007; Hanks 1999; Wood 1982).
Because many cerambycid species are polyphagous, it seems
likely that the volatile cues used by adults to locate hosts are
common to all the host species. Two such compounds, which
are broadly attractive to saprophytic insects in general, are ethanol and the monoterpene α-pinene (Millar and Hanks 2016).
Volatiles emitted by conifers primarily consist of monoterpenes and sesquiterpenes, with α-pinene being a dominant
component (Millar and Hanks 2016). Consequently, αpinene also is a dominant component of the distilled essential
oils of conifers known as turpentines (Byers and Zhang 2011;
Fan et al. 2007; Kozlowski and Pallardy 1997). In contrast,
ethanol is commonly produced by plants that are stressed,
damaged, or dying (e.g., from water deficit or fire), and it
attracts adults of cerambycid species whose larvae require
such hosts (Joseph et al. 2001; Kelsey and Joseph 2003).
Ethanol synergizes attraction to α-pinene for some
cerambycid species, but not others (e.g., Allison et al. 2001;
Chénier and Philogène 1989; Ibeas et al. 2007; Sweeney et al.
2004). Thus, traps baited with either ethanol, α-pinene, or the
combination typically attract only a few cerambycid species in
large numbers (e.g., Byers 2004; Gardiner 1957; Miller et al.
2015a, b; Montgomery and Wargo 1983). Nevertheless, the
combination is commonly, but probably somewhat
J Chem Ecol (2016) 42:631–654
erroneously, considered to be a general “plant volatile” attractant for trapping saprophytic insects (e.g., Campbell and
Borden 2009; Chénier and Philogène 1989; Costello et al.
2008; Kobayashi et al. 1984).
The limited attraction of many cerambycids to blends of
ethanol and α-pinene is no doubt due to these compounds
representing a crude approximation of the complex volatile
profiles of conifers (e.g., Kimmerer and Kozlowski 1982;
Yatagai et al. 2002). Ethanol and α-pinene also may fail to
attract cerambycids that infest deciduous trees, which have
profiles of volatiles that are not dominated by α-pinene. For
these and other hosts, other classes of plant volatiles are likely
to be more reliable cues for locating larval hosts, and the
particular host trees that are in a suitable physiological condition for larval development (see Phillips et al. 1988; Schroeder
and Lindelöw 1989). For example, larvae of some cerambycid
species develop in fire-damaged conifers, and the adults are
attracted to such hosts by the blend of volatiles in smoke
(reviewed by Allison et al. 2004; Suckling et al. 2001). For
these species, attraction may be antagonized by chemicals that
are characteristic of healthy as opposed to fire-damaged trees,
i.e., hosts that are not in a condition suitable for the larvae
(Suckling et al. 2001; Yamasaki et al. 1997). Similarly, volatiles from tree species that are not natural hosts also may
inhibit attraction (Yatagai et al. 2002).
Deciduous hosts do indeed produce volatiles that attract adult cerambycids (e.g., Barata and Araújo 2001;
Coyle et al. 2015; Fujiwara-Tsujii et al. 2012; Hanks
et al. 1996; Liendo-Barandiaran et al. 2010), but there
has been little progress in identifying the specific attractive components. Contributing to the problem is the complexity of the blend of volatile chemicals released by host
plants. For example, Barata et al. (2000) demonstrated
t h a t a n t e n n a e o f th e c er a m b y c i n e P h o r a c a n t h a
semipunctata (F.) can detect more than 40 chemicals in
odor blends from their eucalypt hosts, but the researchers
could not identify two thirds of these chemicals.
Adult cerambycids also may use chemical cues to locate
host plants for their own feeding. For example, adults of the
lamiine Anoplophora malasiaca (Thomson) are attracted to
volatiles released from host plants as a result of feeding by
conspecifics (see Yasui 2009; Yasui et al. 2007, 2008). Some
of these volatiles become absorbed in the beetles’ cuticular
lipids, and in turn serve to attract mates. Thus, the host plant
volatiles directly and indirectly mediate location of both host
plants and mates. Adults of the cerambycine Anaglyptus
subfasciatus feed on nectar and pollen, and use floral volatiles
to locate their hosts (Ikeda et al. 1993). In a screening trial of
floral volatiles, Sakakibara et al. (1998) attracted a few
lepturine and cerambycine species to different chemicals, although the vast majority of species in the local community
were not attracted by any of the baits. This limited response
suggests that the chemicals that were tested may not have
643
simulated the specific blends of floral volatiles that cue attraction of these species.
Pheromones of scolytine bark beetles also serve as
kairomones for cerambycids (reviewed by Ibeas et al. 2007),
guiding them to trees that have had their defenses weakened
by being infested by the scolytine larvae. As a bonus, the
scolytine larvae are preyed upon facultatively by the
cerambycid larvae, providing additional concentrated nutrients (e.g., Allison et al. 2001, 2003; Billings and Cameron
1984; Dodds et al. 2001). Ipsenol and ipsdienol are among
the most common bark beetle pheromone components, and
the most studied (e.g., Seybold et al. 1995; Wood 1982). A
particular bark beetle pheromone may act as a kairomone for
one cerambycid species, but antagonize attraction or be entirely neutral for other species (reviewed by Ibeas et al. 2007).
The response of a cerambycid species to the pheromone of a
particular scolytine species probably is determined by whether
they share host species, and by their coevolutionary history.
That is, pheromones of a scolytine beetle may serve as
kairomones for sympatric cerambycid species, but have no
effect on cerambycids native to other parts of the world, or
that infest hosts other than those attacked by the particular
scolytine species. The response to scolytine pheromones
may be influenced further by plant volatiles such as ethanol
and α-pinene, which may synergize attraction of some species, but have no effect on others (e.g., Miller et al. 2015a, b).
Host Plant Volatiles and Bark Beetle Pheromones
as Synergists or Antagonists of Pheromones
Plant volatiles and bark beetle pheromones may influence
attraction of cerambycids to the aggregation-sex pheromones
produced by their males, perhaps by providing an ecological
“context” to the chemical signal, indicating that the calling
male has discovered a suitable host for the larvae. Again, the
effects of host plant volatiles and bark beetle pheromones on
responses of cerambycids to their pheromones vary widely
(Table S1). Some cerambycid species are not attracted to either their pheromones or host plant volatiles alone, but respond strongly when the two are combined. Others are moderately attracted to their pheromones, with the responses increased additively or synergistically by host plant volatiles.
For a third group, and particularly those species using
female-produced sex pheromones, the pheromone alone is
necessary and sufficient for strong attraction, with host plant
or other volatiles apparently playing no role. For example,
volatiles associated with spruce trees critically synergize attraction of Tetropium species (Spondylidinae) to their pheromones (Silk et al. 2007; Sweeney et al. 2004). Similarly, ethanol and α-pinene and/or bark beetle pheromones critically
synergize attraction of some Monochamus species
(Lamiinae) to their pheromones, whereas for other
Monochamus species they merely enhance attraction, or seem
644
to have no activity (Allison et al. 2012; Fierke et al. 2012;
Hanks et al. 2012; Macias-Samano et al. 2012; Pajares et al.
2010, 2013; Ryall et al. 2015; Teale et al. 2011). For species
whose larvae develop in deciduous hosts, ethanol may enhance attraction to aggregation-sex pheromones, whereas
monoterpenes such as α-pinene (common volatiles of conifers) may be either neutral or repellent (e.g., Collignon et al.
2016; Hanks et al. 2012). Floral volatiles from host plants of
the adults also may influence attraction to pheromone. For
example, floral volatiles critically synergized attraction of
Anaglyptus subfasciatus to the aggregation-sex pheromone
of males, but they were not attractive when tested alone
(Nakamuta et al. 1997).
Optimization of Pheromone Lures and Pheromone-Baited
Traps
The development of pheromone-baited traps as effective practical tools for detection and monitoring of cerambycid beetles
has been contingent upon several interlinked factors, including design of efficient traps; development of lures with release
rates of several milligrams per day; and in some cases, the
release of host plant volatiles with the pheromones. The fact
that some species require a period of maturation feeding before they produce or respond to pheromones (Hanks and
Wang 2016) also may have contributed to earlier failures to
recognize that those species were indeed using pheromonal
attractants. The iterative optimization of trap and lure design
has contributed to the radical paradigm shift that has occurred
since 2004, when it was suggested that cerambycids made
limited use of volatile pheromones (Allison et al. 2004), to
the current situation, where it seems likely that most
cerambycid species use volatile sex or aggregation-sex pheromones. As mentioned above, volatile pheromones have been
identified from more than 100 species, with likely pheromones known from many more species based on trap catches
in pheromone screening trials, and incidental catches in field
experiments targeting other species (Table S1). A more detailed discussion of each of these points is useful in understanding why the elucidation of the chemical ecology of the
cerambycids has lagged far behind that of many other economically important insects.
Trap design is crucial for effective trapping and retention of
cerambycids. During our earliest experiments with
cerambycid pheromones, we soon discovered that sticky cards
and similar traps were ineffective because the relatively large
cerambycids either would not walk on the adhesive, or were
able to extricate themselves from it (Lacey et al. 2008).
Numerous studies have now determined that multiple funnel
traps or cross-vane panel traps, both of which mimic the vertical silhouette of tree trunks, are the traps of choice for
cerambycids (discussed in Allison et al. 2014; Álvarez et al.
2015b; Graham et al. 2012; Millar and Hanks 2016).
J Chem Ecol (2016) 42:631–654
Furthermore, to work effectively, it is essential that all trap
surfaces be coated with the Teflon dispersion Fluon, or other
lubricants, which render trap surfaces so slippery that the beetles cannot alight such that they immediately fall into the collection bucket (Allison et al. 2011, 2014, 2016; Álvarez et al.
2015b; Graham et al. 2010, 2012). This single factor can increase trap capture more than 10-fold (Graham et al. 2010).
Similarly, the inner surface of the collection bucket should be
coated with Fluon so that trapped beetles cannot escape, or
else the collection bucket should contain a killing and preserving solution such as soapy water, saturated brine, or aqueous
propylene glycol (Allison et al. 2014). The Fluon treatment is
durable enough to last for several seasons (Allison et al. 2016;
Álvarez et al. 2015b). We cannot overemphasize the importance of these factors for effective trapping of cerambycids.
Developing lures that can release milligrams of pheromone
per day was a second crucial factor in efficient attraction of
cerambycids that use aggregation-sex pheromones. In particular, males of these species can release >100 micrograms per
male per day of pheromone (e.g., Hanks et al. 2007).
However, because males usually release pheromone only for
a few of hours per day (during their normal activity period)
whereas passive pheromone release devices emit pheromone
continuously, the release devices must emit several milligrams
per day to match or exceed the release rate from a single male.
Thus, pheromone lures for these species typically are made
from permeable plastic sachets or similar devices that can
achieve these release rates. For example, for research purposes, the authors use small, low-density polyethylene resealable sachets loaded with ethanol or isopropanol solutions of
the pheromone as release devices (e.g., Hanks et al. 2014).
Adding a cotton wick (1 × 4 cm dental wick) to sachets helps
to minimize leakage and to stabilize release rates. These sachets seem to have adequate release rates for many
cerambycid pheromones, as judged by trap catches, and they
are cheap and readily available almost anywhere in the world.
However, these sachets are impractical for operational purposes or commercialization because they must be used immediately after they have been loaded, and so are not suitable for
shipping, or storage for extended periods. Nevertheless, for
relatively short term field experiments, their simplicity and
convenience are major assets.
As already discussed, lures must be loaded with tens to
hundreds of milligrams of pheromone so that they will emit
several milligrams of pheromone per day for periods of a week
to several months. Lures that release racemic 3hydroxyhexan-2-one, fuscumol, and other common pheromone components of cerambycid beetles are available from
commercial sources (Synergy Semiochemical Corp., Burnaby,
BC, Canada; Sylvar Technologies Inc., Fredericton, New
Brunswick, Canada; ChemTica Internacional SA, San Jose,
Costa Rica; Alpha Scents, West Linn OR), and in some cases
have been tested under field conditions (Miller et al. 2015b;
J Chem Ecol (2016) 42:631–654
Ryall et al. 2015; Sweeney et al. 2014). Lures that target species of Monochamus with the pheromone monochamol also
are available from commercial sources (Alpha Scents, West
Linn OR; Econex, Murcia, Spain; SEDQ, Barcelona, Spain;
Witasek, Feldkirchen in Kärnten, Austria).
The discussion above of high release rates and consequent
lure design is primarily applicable to cerambycid species that
use aggregation-sex pheromones. The female-produced sex
pheromones of species in the Prioninae and Lepturinae are
emitted in much smaller amounts, so that for at least some
species, lure loadings of a fraction of a milligram remain effective for weeks. In fact, higher loadings may not result in
improved trap catch (Rodstein et al. 2011). For species using
sex pheromones, the authors have used dilute solutions of the
pheromones in plastic sachets as described above, but other
devices, such as heat-sealed plastic tubes, also have proven
effective (Alston et al. 2015; Meier et al. 2016). In general, it is
likely that other commonly used pheromone release devices
such as rubber septa would work for these sex pheromones,
but this may not always be the case. For example, rubber septa
did not work well as release devices for prionic acid, the sex
pheromone of Prionus californicus (Rodstein et al. 2009).
The height at which pheromone-baited traps are deployed
is known to affect catches of lepidopteran species in orchards,
where trees are typically no more than a few meters high (e.g.,
Riedl et al. 1979). This effect may be exacerbated for
cerambycids in forests, where the trees are typically much
taller, in part as a result of the dynamics of the pheromone
plume. However, there is a rapidly growing body of evidence
that stratification of different cerambycid species at different
heights within forests may be a much more important effect.
For example, in field bioassays in east-central Illinois, USA,
five cerambycid species were caught in significantly greater
numbers by traps that were positioned in the forest canopy
(~12 m above the ground) than in the understory, whereas
another three species were caught mostly by traps in the understory (1.5 m above the ground; Schmeelk et al. 2016; also
see Wong and Hanks 2016). Dodds (2014) reported similar
differences among species of cerambycids (and scolytines) as
to whether they were caught in greater numbers by traps in the
forest canopy versus the understory. Additional indications of
stratification were reported in trapping studies in Michigan
(Graham et al. 2010) and New Brunswick, Canada (Webster
et al. 2016). This stratification in the flight patterns of
cerambycids is presumably a consequence of the preferred
feeding, mating, and oviposition sites of various species. For
example, it would be predicted that adults of species that infest
dead wood or roots would be found primarily in the understory, whereas species that feed on foliage of trees and/or whose
larvae develop in the branches of living trees would likely
spend much of their lives within the canopy (Hanks and
Wang 2016). Overall, these studies suggest that unless the
preferred height of a target species is known, traps hung at
645
only one height may result in serious underestimation of the
local population density. It follows that studies that aim to
detect the maximum number of species possible, either for
estimating species richness or for detecting invasive species,
should deploy traps at several different heights. Failure to do
so may result in missing some species altogether.
Another useful discovery with major implications for practical applications of pheromone-baited traps was that pheromone components can be blended to create “generic” lures for
cerambycids, and these lures attract multiple species simultaneously. This effect first became clear during field bioassays
of blends consisting of fewer than 10 cerambycid pheromone
components, in which traps baited with these blends in some
cases caught many thousands of cerambycid beetles of more
than 100 species (Table S1; e.g., USA: Graham et al. 2012;
Handley et al. 2015; Hanks and Millar 2013; Hanks et al.
2007, 2012; Australia: Hayes et al. 2016). Ongoing field
screening trials conducted by the authors’ collaborators in
Asia, Europe, and South America are yielding similar results.
Thus, in at least some cases, a series of traps, each of which
would have been baited with a single pheromone, now can be
replaced by a single trap baited with a blend of pheromones of
many species, resulting in cost savings in terms of both materials and labor. Obviously, these generic lures have major implications when the goal is to attract as many species as possible, for example in surveillance efforts to detect incursions
of invasive species or in surveys of species richness (e.g.,
Graham et al. 2012; Handley et al. 2015; Hanks and Millar
2013). For the majority of the known pheromone components,
it also is useful that their chemistry is such that they are unlikely to react chemically with each other when mixed in
blends, particularly if they are formulated in a diluent such
as isopropanol
The use of multispecies pheromone blends is most effective when there is the least likelihood of the blend of components producing heterospecific behavioral antagonism, which
would otherwise reduce attraction and trap catch of many of
the targeted species. Optimal multispecies attraction is therefore achieved when the components are from more distantly
related species in different subfamilies (i.e., the chemistry of
the pheromones is completely different), and/or when the
pheromones are of different types (i.e., aggregation-sex pheromones versus sex pheromones). Using blends of closely related species’ pheromones for multispecies trapping is illadvised because closely related species frequently share pheromone components; recent studies have shown that analogous
to the pheromone blends of other insect taxa, the attractiveness
of cerambycid pheromone blends can depend strongly on the
presence of minor components, either as synergists for conspecifics or as behavioral antagonists reducing the attraction
of heterospecifics (e.g., Hanks and Millar 2013; Meier et al.
2016; Mitchell et al. 2015; Ray et al. 2012b, 2015). These
synergistic and antagonistic effects provide mechanisms for
646
maintaining the species specificity of signals among sympatric
species whose pheromones are dominated by the same single
compound. Thus, if the goal is to attract a single species most
effectively, then an accurate reconstruction of its pheromone
blend should be used. Conversely, if the goal is to attract the
maximum number of species with the minimum investment in
materials and labor, then formulating mixtures of the pheromone blends of many species will be most cost effective.
However, it must be clearly understood that use of such blends
may limit or prevent the attraction of species that are strongly
inhibited by one or more components. The roles of, and interactions between, minor components of pheromone blends
merit further study to assess the extent to which such inhibition may affect trap catches.
Applications of Semiochemicals in Detection, Monitoring,
and Management of Cerambycid Beetles
Pheromones and other semiochemicals have several important
uses in insect management, including detection of one or more
particular species, monitoring population densities or seasonal
phenology of a particular species, and control of a particular
species (Millar 2007). The first of these two applications overlap considerably and are thus considered together.
Use of Pheromones for Detection and Monitoring of
Cerambycids Two of the major advantages of pheromonebaited traps are their sensitivity and their selectivity, both of
which have been exploited in the detection of cerambycids.
There are several different scenarios in which pheromonebaited traps can be used to advantage in detecting lowdensity populations. First and foremost is the detection of
exotic species. The problem of exotic species being inadvertently introduced into new areas of the world is particularly
pernicious for cerambycids because their long-lived larvae,
concealed within the wood of packing cases, dunnage, pallets,
or other wooden materials, are readily transported by international commerce. Thus, species such as the Asian
Anoplophora glabripennis have invaded North America and
Europe, with the potential for causing devastating losses of
hardwoods. Similarly, the Asian species Aromia bungii
(Faldermann) has recently invaded Europe (EPPO 2014) and
Japan (Kiriyama et al. 2015), where it represents a major threat
to fruit trees. For these and numerous other species of
cerambycids, semiochemically baited traps may be powerful
tools for detecting new incursions as well as monitoring range
expansions and the success of eradication efforts. For example, pheromonal attractants are now known for
A. glabripennis (Zhang et al. 2002), Callidiellum rufipenne
(Zou et al. 2016), and Tetropium fuscum (Sweeney et al.
2010), all of which have invaded North America.
Conversely, pheromonal attractants are available for North
American species that have invaded Europe, such as
J Chem Ecol (2016) 42:631–654
Neoclytus a. acuminatus (Lacey et al. 2004) and several species of Monochamus that have invaded various parts of the
world (Table S1). Furthermore, at the time of writing, the
authors and their collaborators also have tentatively identified
pheromones for several other potentially invasive Asian species, including Anoplophora chinensis (Hansen et al. 2015),
Callidiellum villosulum (Wickham et al. 2016b), Xylotrechus
rufilius Bates (Narai et al. 2015), as well as A. bungii and
Trichoferus campestris (Faldermann) (unpub. data).
Semiochemically baited traps also are finding increased
use for monitoring populations of species within their native
range, such as Monochamus galloprovincialis, the primary
vector of the lethal pinewood nematode in Europe (Álvarez
et al. 2015b; Rassati et al. 2012). Historically, cerambycids
that could cause damage to timber and cut logs have been
monitored with traps baited with common host plant volatiles
such as α-pinene or turpentine (reviewed in Allison et al.
2004; Millar and Hanks 2016). However, the recent and ongoing identifications of pheromones for several economically
important species coupled with concurrent improvements in
trap design have improved the efficiency of trapping many
fold, and so it seems likely that pheromone-baited traps will
rapidly supplant use of traps baited only with host plant compounds or other kairomonal attractants.
In addition, pheromone traps may be the most powerful
tools available for detecting and monitoring populations of
endangered or threatened cerambycid species, such as the
iconic Rosalia alpina (L.), a European species that has been
red-listed by the International Union for Conservation of
Nature (http://www.iucnredlist.org/details/19743/0), or the
valley elderberry longhorned borer, Desmocerus californicus
dimorphus, in the western USA (Ray et al. 2014). For the
latter species, a small survey of several populations with
pheromone-baited traps collected more beetles than the entire
number held in collections when the species was first listed as
threatened by the United States Fish and Wildlife Service (Ray
et al. 2014). Similarly, field studies using pheromone-baited
traps frequently result in new state records for cerambycid
species. For example, of the 69 cerambycid species caught
during a study in Delaware, USA using traps baited with a
generic pheromone blend, seven species represented new state
records (Handley et al. 2015).
More generally, cerambycid species perform valuable ecosystem services as primary decomposers of woody biomass
and they can be important indicators of ecosystem health (e.g.,
Maeto et al. 2002). In this context, semiochemically baited
traps are powerful tools for conducting surveys of species
richness and abundance (e.g., Dodds et al. 2015; Graham
et al. 2012; Handley et al. 2015; Hanks and Millar 2013;
Hayes et al. 2016; Sweeney et al. 2014; Wickham et al.
2014). They may be particularly useful for surveying species
in the forest canopy because these species could easily be
missed in ground level surveys conducted by other means.
J Chem Ecol (2016) 42:631–654
Use of Pheromones for Control of Cerambycid Beetles For
insects in general, three main pheromone-based control strategies have been developed. These include mating disruption
with sex pheromones, attract-and-kill using attractants in association with insecticides or pathogens, and mass trapping
using traps baited with pheromones, often in combination
with host volatiles. The choice of which method to use is
dictated by the natural history of the target species, and of
course, economics. For example, mating disruption may be
most suitable for managing species in which the females produce powerful sex pheromones, because it could prevent them
from attracting mates. Nevertheless, mating disruption may
still be effective with species that use male-produced aggregation-sex pheromones, as demonstrated in a study in which
aerial application of fuscumol-impregnated dispensers over
forested areas resulted in significant reductions in populations
of Tetropium fuscum (Sweeney et al. 2011a).
In terms of economics, the cost of synthesizing, formulating, and deploying pheromone release devices area-wide for
mating disruption often may not be competitive with control
using insecticides or deployment of plants engineered to produce insecticidal toxins, particularly in crops grown on very
large acreages with low profit margins. When viewed in this
light, it seems unlikely that pheromone-based mating disruption would be a feasible strategy for use over huge areas, such
as in controlling cerambycid species that are pests of forest
trees. However, mating disruption could indeed be feasible,
and possibly even crucial, for suppression or eradication of
newly established invasive species that are limited to small
geographic areas.
Several pheromone-based strategies have now been tested
for control of cerambycid species, with promising results. For
instance, mating disruption has been tested twice with Prionus
californicus, the females of which produce the powerful sex
pheromone prionic acid in nanogram quantities that can attract
males from hundreds of meters away. In a preliminary test in
hop yards, the number of males that reached a pheromonebaited sentinel trap was reduced by 84 % when the sentinel
was encircled by pheromone lures at distances of 18 or 36 m,
compared to the number of males reaching a similar sentinel
encircled by lures containing only solvent (Maki et al. 2011a).
A similar trial in a sweet cherry orchard was even more promising, with pheromone lures reducing by 94 % the number of
males reaching a pheromone-baited sentinel trap (J. D.
Barbour, pers. comm.). Prionus californicus has a long and
asynchronous life cycle (3–5 years), so it may take several
years for the effects of mating disruption to be fully realized.
Nevertheless, in the latter case, it was noted that after two years,
catches of males in monitoring traps had decreased more than
seven-fold, suggesting that the strategy was indeed effective in
suppressing the local population (Alston et al. 2015).
Researchers have been experimenting for several decades
with using entomopathogenic fungi (e.g., Hajek and Bauer
647
2009; Petersen-Silva et al. 2015, Sweeney et al. 2013) or nematodes (e.g., Li et al. 1989) for control of cerambycids, including experimenting with attract-and-kill techniques using host
plant compounds as the attractant (Li et al. 2007). However, to
our knowledge, attract-and-kill using pheromones as attractants and pathogens as the killing agent has not yet been reported for any cerambycid species, although such experiments
may be in progress (e.g., see Álvarez-Baz et al. 2015). This
technique could prove to be useful for auto-disseminating either fungal conidia or nematodes throughout a population,
using either sex or aggregation-sex pheromones as the attractants. In the latter case, both sexes would be contaminated
with pathogens upon being attracted to traps, whereas in the
former case, dissemination of pathogens to females would
occur only during mating with contaminated males.
Mass trapping has been explored for control of cerambycid
pests in several systems. In a preliminary trial using the
female-produced sex pheromone of Prionus californicus,
deploying pheromone-baited traps around a central baited sentinel trap decreased by 88 % the number of males caught by
the sentinel trap (Maki et al. 2011a). Even more promising, a
longer term experiment testing control of P. californicus in
sweet cherries showed that after five consecutive years of
mass trapping, trap catches in monitoring traps were reduced
from 265 to 2 male beetles (Alston et al. 2015). These data
suggest that exertion of continuous trapping pressure on this
univoltine species, which reproduces relatively slowly due to
its long life cycle of several years, can indeed drive populations to low levels, as occurs in mass trapping of large tropical
weevils (Faleiro 2006; Oehlschlager 2016, this issue).
Furthermore, mass trapping may be a viable strategy for other
prionine species that have long life cycles, such as the sugar
cane pest Dorysthenes granulosus that is readily caught by
using simple pheromone-baited pitfall traps consisting of
vertical-sided holes dug in the ground (Wickham et al. 2016a).
Mass trapping trials also have been conducted with two
species that have aggregation-sex pheromones. Grids of
pheromone-baited traps resulted in lower infestation rates
of the invasive species Tetropium fuscum in bait logs
(Sweeney et al. 2011b). However, this method might only
be useful for treating spot infestations because the
10 × 10 m spacing of the traps would likely be prohibitively expensive to deploy over larger areas. The European
lamiine Monochamus galloprovincialis, a primary vector
of pine wood nematode, also may be targeted for mass
trapping using lures consisting of a blend of the pheromone
monochamol and bark beetle pheromone synergists, optimized over many years by Pajares and coworkers (e.g.,
Álvarez et al. 2015b). The lures currently are widely used
in Europe to monitor for this pest (e.g., Rassati et al. 2012),
but are so effective that trap densities of less than one trap
per hectare may reduce beetle population densities by 95 %
(Sanchez-Husillos et al. 2015). As an added bonus,
648
because the pheromone is highly conserved within the genus Monochamus (as discussed above), monochamol is the
aggregation-sex pheromone of congeners in Europe that
also may vector the pinewood nematode. Thus, these species also are strongly attracted to the lure, so the single lure
and trap should be effective against multiple species.
Summary
Based on the studies described herein, it seems likely that
cerambycid pheromones will find use in numerous applications,
including ecological studies assessing insect communities in
different habitats, detection and estimation of the ranges of rare
or threatened species, detection and eradication of invasive species, and management of pest species, be they native or exotic.
To date, the development of practical applications for
cerambycid pheromones has lagged behind that of many other
insect groups, for several reasons. For example, it is only in the
last decade that it has become clear that, as with so many other
insect species, volatile pheromones are crucial mediators of
cerambycid reproduction, and these pheromones should be
readily exploitable for management of pest species. This paradigm shift has come about in part as a consequence of the
“explosion” in the identifications of cerambycid pheromone
structures, with sex or aggregation-sex pheromones now known
from all five of the major subfamilies within the Cerambycidae.
In tandem with the rapidly growing database of pheromone
structures (Table S1), great improvements in methods for their
practical application have shown that semiochemically based
tools can be far more effective than the detection, monitoring,
or control methods that they could replace.
Few cerambycids are crop pests, so sources of grant funds
for studying these insects are less obvious and less available
than for important pests of major crops such as corn or soybeans. However, we suggest that the work summarized in this
review makes a compelling case for the continued development and incorporation of semiochemicals into programs for
detecting, controlling, and where necessary, eradicating exotic
cerambycid species.
We also suggest several areas for future research. First, it is
clear that there are numerous additional pheromone structures
waiting to be identified, and there are still no pheromones
identified from the small subfamilies Parandrinae,
Necydalinae, and Dorcasominae. Further identification of
new pheromones has obvious practical implications, but in
addition, the new structures will help to flesh out the developing picture of pheromone types and pheromone use within the
family, and it is likely that pheromone structures can be used
in systematic studies of the evolutionary relationships among
species, genera, and tribes. Furthermore, because of the conservation of structures within closely related taxonomic
groups, a more detailed plan of pheromone use within the
J Chem Ecol (2016) 42:631–654
family will increase our ability to predict whether a species
uses volatile pheromones, and if so, whether they are maleproduced aggregation-sex pheromones or female-produced
sex pheromones, and what their general structures are likely
to be. This information would be invaluable for rapidly developing pheromone-based tools for detecting, tracking, and
eradicating new exotic invaders before they have a chance to
spread widely.
Second, the explosion of identifications of cerambycid semiochemicals is rapidly outpacing our understanding of the
roles of these compounds in the ecology of the beetles and the
interactions of species with other members of their communities. For example, it remains unclear why the three subfamilies
Cerambycinae, Lamiinae, and Spondylidinae seem to have
only aggregation-sex pheromones, whereas based on the relatively few pheromones identified from the Prioninae and
Lepturinae, these two subfamilies may have only femaleproduced sex pheromones. Numerous other biological and
ecological questions abound, such as why some species are
attracted to the pheromones of congeners, or why some species produce what seem to be pheromones, but there is no
evidence that they are attracted by these compounds.
Third, although there have been major advances in trap
design, the pheromone lures may still be a weak link in at
least some cases. To be widely adopted, pheromone lures must
have effective lifetimes of several weeks, and they must be
robust, with reasonable shelf life, and be suitable for shipping.
This is clearly an area in which improvements can be made.
We also suggest that the implications of pheromone
chemistry in the success or failure of invasion biology warrants careful investigation. That is, if indeed pheromonal
communication by an exotic species is essentially blocked
by similar or identical pheromones produced by much more
abundant native species, this natural form of mating disruption will reduce the chances of establishment and spread of
an invader. Conversely, an exotic species that does not overlap in pheromone chemistry with native species, which
therefore is free to invade a “pheromone-free space”, will
be more likely to become established. Thus, we suggest that
the pheromone chemistry of an exotic species and its overlap in pheromone chemistry with native species should be a
factor to consider in developing risk assessments for potentially invasive exotic species.
Overall, the rapid expansion of research on cerambycid
semiochemicals over the past decade has opened a new window into the biology and ecology of this large and diverse
insect family. This new expansion has been most timely because of the increasing problems worldwide with exotic
cerambycids as devastating invasive pests. We hope that this
review serves as a useful reference for the increasing number
of researchers and regulatory personnel working to understand
the chemical ecology of cerambycids, and as needed, to manage their populations.
J Chem Ecol (2016) 42:631–654
Acknowledgments The authors are grateful for the many students,
technicians, postdoctoral and visiting scholars, and collaborators who
contributed so extensively to much of the research described herein. We
also appreciate helpful comments on the manuscript from reviewer Jon
Sweeney. We thank the numerous funding sources which have supported
our work on cerambycid semiochemistry over the past 12 years, including
the United States Department of Agriculture (USDA) - Animal and Plant
Health Inspection Service, the USDA CSREES National Research
Initiative, National Institute of Food and Agriculture, Western Regional
Integrated Pest Management Fund, North Central Region Integrated Pest
Management Center, and the Alphawood Foundation of Chicago. JGM
also gratefully acknowledges ongoing funding from Hatch Act project
CA-R*ENT-5181-H.
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