Download Hawai`i: A Natural Entomological Laboratory

Hawai'i: A Natural Entomological'Laboratory
Chris M. Simon, Wayne C. Gagne, Francis G. Howarth,
and Frank
J.
Radovsky
W
ell over 90% of Hawai'i's plants and animals are
endemic. This special character of Hawai'i is due
to its largely volcanic origin and its location
some 2,500 miles from the nearest continent. Many groups
of organisms never became established on the islands, but
derivatives of the few species that did colonize Hawai'i
evolved in amazing ways. The isolated island environment,
in which evolution seems to have proceeded more rapidly
than in continental areas, creates a natural laboratory that
has fostered many fruitful scientific studies.
The main Hawaiian Islands form the southernmost section
of a chain of islands and seamounts that stretches nearly to
the Bering Sea. The entire chain sits on the Pacific Tectonic
Plate which moves northwestward-approximately
4 inches
per year-as the sea floor spreads. The islands and seamounts were formed by the periodic venting of lava as each
passed over a stationary volcanic "hot spot." The northern
Emperor Seamounts are the most ancient extant derivatives
of the hot spot. South of these undersea mountains lie numerous atolls, small rock islands, and, finally, the more familiar "high
Semiterrestrial Hawaiian damselfly naiad, Megalagrion,
prob. koalense (Blackburn), that lives on O'ahu in leafaxils
of 'ie' ie (Pandanaceae: Freycinetia arboreal; note highly
modified, heavily sclerotized gills of the naiad. (Photo by
William P. Mull.)
FALL 1984
islands":
Ni'ihau,
Kaua'i, O'ahu,
Maui, Lana'i,
Molaka'i, Kaho'olawe, and Hawai'i. The island of Hawai'i, the
largest island in the entire chain, is currently near the hot
spot and thus is volcanically active (Normark et al. 1982).
The oldest of the major high islands in the Hawaiian Chain
is Kaua'i, approximately 6 million years old; its knife-edged
ridges and deep valleys record millenia of ewsion. The youngest is Hawai'i, which first emerged from the sea about
700,000years ago and which is still growing. Its youth is characterized by a lack of erosion and surface streams on the two
dome-shaped volcanoes that constitute the southern portion
of the island. The rounded form of Mauna Loa belies its claim
to being the most massive mountain in the world (measured
from the sea floor). A new potential island, L6'ihi, is forming
off the southeast coast of Hawai'i and is predicted to rise
above the surface of the sea within a few tens of thousands
of years (Normark et al. 1982).
The method of island formation described above dictates
that seamounts and islands in the Hawaiian Chain will be
arranged in strict chronological order, progressively older to
the northwest. However, two of the smaller formations in
the northwestern portion of the Hawaiian Chain, Necker Island and Wentworth Seamount, are anomalous. They are
much older than the neighboring islands and seamountS.
Rocks dated at greater than 70 million years place the origin
of these volcanic mountains in the South Pacific Ocean. They
subsequently moved north on the Pacific Plate to be incorporated into the Hawaiian Archipelago (Rotondo et al. 1981).
One biogeographical theory for the origin of the Hawaiian
biota, the island integration theory, suggests that some colonizing species could have ridden north on these islands.
9
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One major problem with this explanation is that it is not
known whether the rocks were above sea level at all times
during their migration.
The island integration theory combines aspects of vicariance and dispersalist biogeographical theories. A strict vicariance biogeographical explanation for the origin of all or
part of the Hawaiian biota is unlikely but has nevertheless
been suggested. This theory suggests that a pan-Pacific continent, Pacifica, was the home of an ancestral biota that was
fractionated and subsequently changed when the major portion of the land area broke up and migrated (Melville 1981).
This theory has been largely rejected because of shaky geological evidence and mismatches in the timing of origination
versus colonization of taxa (Haugh 1981).
The most likely origin of the Hawaiian biota was via longdistance dispersal across thousands of miles of ocean. These
long-distance colonists must necessarily have relied on transport by either water, wind, or birds (or even bats or insects)
(Zimmerman 1948a). Rafting appears to be important in dispersal to and among islands, but the remoteness of the Hawaiian Islands and their position in relation to major ocean
currents appears to have considerably diminished its significance. For example, coconuts float across considerable
oceanic distances and remain viable, but coconuts did not
10
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reach Hawai'i until brought by the Polynesians. Trade winds
from the northeast, a high-altitude jet stream from the west,
and occasional cyclonic storms may carry living organisms;
by designing ship- and airplane-trapping programs, the late
J. Linsley Gressitt of the Bernice P. Bishop Museum (BPBM)
was able to document a rich array of "aerial plankton"small insects, seeds, spores, and other organisms (Gressitt
and Yoshimoto 1964, 1974).
Carlquist (1982) has suggested that the major agents for
the arrival of seeds and fruits were migratory birds. Oceanic
birds nested in large numbers in the past throughout the
archipelago, and some shore and water bird species are regular migrants. Whatever the colonization mechanism, the
most striking aspect of organisms getting to Hawai'i is the
infrequency of founding events needed to explain the known
biota: for each of the major biotic groups, the frequency is
calculated in tens of thousands of years (Zimmerman 1948a,
Montgomery 1982).
There are four conspicuous groups of Hawaiian Island colonizers: plants, arthropods, land snails, and birds. There are
no native freshwater fish with the exception of those whose
recent ancestors came from the sea. There are no native amphibians or terrestrial reptiles, and only one nonmarine
mammal, the Hawaiian bat (in addition, a new subfossil bat
species has been recently discovered). Visiting entomologists are at first struck by the absence or poor representation
of many continental groups in the native entomofauna. Several orders, including Ephemeroptera, Isoptera, Plecoptera,
Mecoptera, and Tricoptera, and about 85% of the world's
insect families are not even represented. Thus the native
fauna appears quite depauperate at the familial and ordinal
level in comparison with mainland taxa; however, successful
BULLETIN
OF THE ESA
Hawaiian colonizing groups are characterized by a high diversity of endemic species-a repeated pattern of rampant
speciation beginning with a single founding species.
Rapidly evolving diverse species assemblages are ideal
subjects for studying evolution. Hawaiian species, especially
the Hawaiian pomace flies (Drosophilidae), have served as
experimental genetic systems and have been the basis for
the newest models of speciation (Carson and Templeton
1984).These genetic models entail the establishment of small
founding groups of individuals that have become geographically isolated from the parental populations. Many unsuccessful "founder events" occur. Many founding groups go
extinct and some remain identical to their parental stock, but
a few-those that contain individuals with the proper genetic
background-survive
and produce new species.
Founder-type speciation-called
transilience by Templeton (1980)-is thought to be especially prevalent in (but
not restricted to) Hawai'i due to the rugged terrain and plentiful microenvironments that are often separated from similar
microenvironments by large distances, the absence of many
competing species that could destroy the incipient founder
population, the disrupting influence of lava flows, and the
separation of the islands themselves. Drosophila may be
preadapted for this type of speciation because of their elaborate lek-type mating behavior (Spieth 1966,1968),their population structure (Templeton 1980), and their breeding-site
specificity (Montgomery 1975, Heed 1971). Other Hawaiian
insects, not yet investigated, can be expected to exhibit similar or additional transilience-facilitating qualities.
There are 484 described species of endemic Hawaiian Orosophilidae. Approximately 200 more species in local collections remain undescribed. These plus those species yet to
fALl. 19H4
Vulcanism is a continuing background for Hawaiian biotic
evolution:
Firepit at Mauna Ulu in the rift zone of Kilauea
Volcano. (Photo by F. J. Radovsky.)
be discovered make up an estimated 800species, almost onethird of the world's drosophilid species. This diverse assemblage is believed to have originated from one or two colonizing species.
The best studied of the Hawaiian drosophilids are the
slightly more than 100 picture-winged Drosophila, so called
because of their heavily patterned wings. These are the
largest Drosophila in the world and exhibit the most elaborate courtship displays.
A team of evolutionary biologists from Hawaii and elsewhere has spent nearly two decades investigating diverse
aspects of Hawaiian Drosophila biology: behavior, biochemistry, developmental biology, ecology, morphology, genetics
(classical and molecular), physiology, and systematics. This
research began in 1948 under the encouragement of Elwood
Zimmerman (then at BPBM). with the pioneering taxonomic
work of D. Elmo Hardy of the University of Hawaii (UH). By
1963, Hardy had encouraged scientists at the University of
Texas to join the project and Hawaiian Drosophila research
mushroomed (Hardy 1974, Spieth 1981).
Some of the most exciting evolutionary research to emerge
from the Hawaiian Drosophila project centers on chromosomal phylogenies based on banding patterns of the giant
salivary chromosomes worked out by Hampton L. Carson
(UH) (reviewed in Carson 1983). With this phylogenetic hypothesis as a base, Carson and co-workers are taking a close
11
look at the speciation process. Carson in collaboration with
Kenneth Kaneshiro (UH) is currently studying the genetic
basis of mating behavior. Kaneshiro has developed a theory
that allows the recognition of ancestral versus descendant
populations based on nonreciprocal mate preferences (Kaneshiro 1983).
Basic research on Hawaiian drosophilids will undoubtedly
aid in solving pest-management problems, as it in fact has
already done. Arita (1983, Arita and Kaneshiro 1983) found a
lek-type mating behavior in the Mediterranean fruit fly strikingly similar to that of Drosophila. The significance of this
finding for integrated pest management is that the nonrandom distribution of fruit flies suggested improvements in
the established survey detection program. Furthermore,
Arita found that laboratory-reared sterile males did not exhibit lek-type mating behavior and would thus be less effective in mating than wild males.
Other researchers currently working with Hawaiian Drosophila study mitochondrial
DNA evolution (A. R. Templeton, L. V. Giddings, and R. DeSalle, Washington University, St. Louis, Mo.), nuclear DNA evolution (]. A. Hunt and
W. D. Stuart, UH), DNA sequencing of yolk proteins (M.
Kambysellis, New York University), patterns of gene regulation (]. Dickenson, University of Utah), numerical phylogenetic systematics based on morphological characters (]. W.
Archie and C. W. Simon, UH), and oviposition behavior and
its relationship to generalist/specialist strategies and speciation (A. Ohta, UH).
Ohta (in Carson and Ohta 1981) has investigated the genetic basis of egg-laying behavior by testing hybrid females
for host specificity. His work makes use of Drosophila grimshawi Oldenberg, one of two picture-winged species known
to occur on more than one island (the other is D. crucigera
Grimshaw; note that closely stituated Maui, Moloka'i, and
Lana'i are considered an island complex rather than separate
entities). On Kaua'j and O'ahu, D. grimshawi is a specialist
(on Wikstroemia; Thymeleaceae); on Maui, it is a generalist
(feeding on plants in 12 different families). Ohta has evidence
to suggest that the genetic basis of host shifts may be regulated by a single gene, explaining how adaptive shifts can
occur rapidly and provide a beginning for the speciation process.
Many species of picture-winged Hawaiian Drosophila are
specialists whose larvae feed on only one plant species (Heed
1971, Montgomery 1975). In order to breed many of the species in the laboratory it is necessary to include extracts of
their host plant in the larval food medium. Other species,
such as the Cheirodendron
(Araliaceae) leaf breeders, have
amazingly similar breeding requirements; up to 15 species
have been reared from the rotting leaves of a single tree
species (Heed 1971).
Perhaps the most interesting example of host-plant specialization in the Hawaiian Drosophilidae is that found in the
closely related Drosophila si/varentis Hardy and Kaneshiro
and D. heedi Hardy and Kaneshiro on the island of Hawai'i.
D. silvarentis breeds only in the yeasty slime fluxes of a native
tree, Myoporum
sandwicense
(Myoporaceae). D. heedi
breeds only in the soil that has been moistened by these
same dripping fluxes. Chromosomally the two differ by one
inversion, derived in D. heedi. Three other species, found
on Maui (D. gymnobasis Hardy and Kaneshiro), Kaua'i (D.
musaphi/a Hardy), and a different volcano on Hawai'i (D.
hawaiiensis Grimshaw), have chromosomal banding patterns
identical to D. silvarentis but the last two feed on an entirely
unrelated host plant, Acacia koa.
12
Contrasting mechanisms of insular speciation among phytophagous insects may have as their fundamental bases the
relative host specificity of the founding species. Among Hawaiian insects there are suites of congeneric species restricted to one plant genus or family, for example the large
genus Nesiomiris, which comprises an array of host-specific
species associated with a narrow range of related plant species (Gagne 1982). Specialists such as Nesiomiris probably
arose from specialist ancestors. In contrast, large genera
probably arising from "generalist" colonists now demonstrate an array of host-specific species that exploit a wide
range of unrelated plant species, for example Sarona,
Sulamita, and Plagithmysus. One Hawaiian nabid bug is both
a generalist and a specialist. Nabis truculentus (Kirkaldy) lives
only on the shrub Pipturus albidus (Urticaceae); yet the bug
is a generalist predator that feeds on any insects it is able to
catch.
Why do some colonists speciate while others do not? We
have only two endemic
butterflies,
Vanessa tamehameha
Eschscholtz and Udara (Vaga) blackburni (Tuely), but over 900
moths. The answer may lie in the fact that both butterflies
utilize host plants that are widespread here and both are
highly vagile so that gene flow seems to be uninterrupted
within and among the islands.
We have over 140 species of native cerambycids in three
genera (Gressitt 1978). All but two of these species belong to
the phytophagous genus Plagithmysus. The remaining longhorned beetle species, Megopis reflexa (Karsch) and Parandra
punctipes
Sharp, are both detritivores, feeding in rotting
logs. Why is one genus species rich while the other two are
monotypic? In this case the reasons could be tied to food
plant specificity.
Lack of speciation obviously does not always indicate recentness of arrival in the archipelago. It may also result from
any of a multitude of biological factors: vagility, host range,
distribution of food resources within the archipelago, genetic structure of individual populations, interactions with
predators, and chance factors, which singly or in concert
deter speciation.
Adaptive Shifts
Truly unusual adaptive shifts have been discovered in the
Hawaiian entomofauna. For example, there is a radiation of
ambush predators in the larvae of the moth genus Eupithecia
(Geometridae) (Montgomery 1982). No other Lepidoptera in
Drosophila cyrtoloma (Hardy) from Maui, one of the largest
ca. 7 mm in body
of the giant picture-winged
drosophilids,
length. (Photo by W. P. Mull.)
BULLETIN OF THE ESA
the world exhibit such behavior. Equally bizarre are a drosophilid, genus Titanochaeta, predaceous on spider eggs
(Heed 1968, Carson 1971),a predatory alpine "seed bug" that
feeds upon dead insects and other windborne debris (Howarth and Montgomery 1980, Ashlock and Gagne 1983), a
riparian Nabis (Gagne 1986), arboreal saldids (Cobben 1980),
an undescribed stem-boring amphipod found in the native
greensword (Howarth 1982), leaf-mining tipulids (Hardy
1960), and crane flies "turned phalangid" through loss of
wings (Gagne 1975a, Byers 1983, 1985).
Hawaiian damselfly naiads of the genus Megalagrion have
radiated and shifted to occupy as many habitats as are found
in all the rest of the order Odonata. Megalagrion larval habitats with associated numbers of species (in parentheses) are
riffles (3); flowing streams (3); streamside pools and wet
banks (2); open ponds and paddies (3); under vegetation in
puddles, swamps, and bogs (2); wet rocks and dripping
banks (2); water- and detritus-catching leafaxils (2); terrestrial leaf litter (1); and unknown (11) (Zimmerman 1948b, Maciolek and Howarth 1982). The species that was most widespread at the beginning of this century was M. pacificum
(McLachlan). Because of the introduction of mosquito fish
and habitat degradation, it is now known only from two isolated streams in Kipahulu Valley (Moore and Gagne 1982).
The larval hosts of the largest endemic Lepidoptera genus,
Hyposmocoma with ca. 350 spp., range over nearly all of the
possible plant groups from lichens, mosses, and ferns
through many native Hawaiian angiosperms (Zimmerman
1978). These gelechiids forage on rocks and tree bark, build
tunnels in mosses, and bore in stems and wood. A few are
at the verge of an aquatic existence-living
on rocks and
along streams (Gagne and Howarth 1984).
An unexpected wealth of radiating cavernicolous arthropods has been found in Hawaiian lava tubes. These tubes
were viewed as sterile and unsuitable for life, until Frank
Howarth serendipitously discovered cave-adapted insects in
1971. Since that time, he has brought to light nearly 50 troglobitic organisms feeding on tree roots, fungi, organic colloids, other inhabitants, and transients. The Hawaiian troglobites exhibit characteristics similar to cave species in other
parts of the world, involving modifications of behavior, physiology (water balance and metabolic rates), and morphology
(loss of eyes and body pigments, reduction or elimination of
wings, and hypertrophication of chemosensory and tactile
organs) (Ahearn and Howarth 1982, Hadley et al. 1981).
The adaptation of arthropods to lava tubes more frequently
occurs in those taxa having progenitors with cryptic nocturnal habits: crickets, thread-legged bugs, wolf spiders, and
millipedes (Howarth 1983a).Their ancestors were in essence
primed to face an environment characterized by darkness,
high humidity, stable temperatures, and rocky substrates.
Other species such as the lava tube-inhabiting cixiid planthopper, Oliarus polyphemus
Fennah, may have been preadapted for cave invasion via paedomorphic evolution; the
juveniles of the closely related epigean rain forest cixiid, Oliarus inequalis Gifford, are subterranean and have reduced
eyes (Ahearn and Howarth 1982). The troglobite may have
simply retained these juvenile features in the adults to become an obligate and permanent cave dweller.
Howarth (1972,1980,1983a)quelled the conventional belief
explaining the evolution and distribution of obligate cave
species as ancient relicts that evolved from populations of
troglophiles (facultative cave species) isolated in caves after
their surface populations were extirpated by changing climatic conditions (e.g., glaciation). Thus a phenomenon (cave
FALL 1984
Udara (Vagal blackburni (Tuely) (Lycaenidae), one of the
two widespread, endemic Hawaiian butterflies, sitting on one
of its host plants (Dodonaea eriocarpa). (Photo by W. P.
Mull.)
adaptation) once considered a special case in nature is now
recognized as consistent with more general evolutionary
processes. Troglobites can now be predicted to occur in any
cavernous region in which the environment has allowed the
continuous inhabitation of the subterranean system over an
evolutionary time span.
One adaptive shift found on islands throughout the world
is flightlessness. It is found in Hawai'i not only among insects
but in birds (extinct ducks, geese, rails, and ibis) and plants
(i.e., loss of dispersal mechanisms such as hooks, buoyancy,
small size). Although there are numerous flightless arthropods and vertebrates in continental habitats, the striking feature of flightlessness on islands is that it often involves normally volant taxa.
Elwood Zimmerman (1957) considered the brown lacewings (Hemerobiidae) to be "among the marvels of insular
creation." His high esteem for this group resulted from the
occurrence of several flightless species in the genera Pseudopsectra and Nesothauma, wherein we find curious beetlelike and spiny ground-dwelling forms with forewings hardened into tough protective coverings. Such species are considered to have independently
arisen from the more
widespread volant genus Nesomicromus.
Flightless Hawaiian species have evolved in 10 of the 11
native orders of volant insects: Coleoptera, Orthoptera, Thysanoptera, Psocoptera, Heteroptera, Homoptera, Neu rop13
Zimmerman (1960) described what he thought was the
most spectacular case of rapid evolution in Hawaiian insects-four species of closely related pyralid moths of the
genus Hedylepta apparently host specific to bananas. Bananas were first introduced into the Hawaiian Islands by the
Polynesians less than two millenia ago. Gagne and Howarth
(1984; K. Sattler, personal communication) believe that this
case may not be as clearly defined as was at first suspected;
they suggest that these four species of Hedylepta were already associated with endemic monocots when the Polynesians arrived. Just as the coconut leafroller, Hedylepta blackburni (Butler), and the sugar cane leafroller, H. accepta
(Butler), switched from native palms and grasses, respectively, and now attack primarily those alien hosts indicated
in their common names, the four "banana Hedylepta" may
have switched from the native fan palms, Pritchardia spp., or
from joinvillea
(Joinvilleaceae), or perhaps from another
large-leaf monocot now extinct. Hedylepta asaphombra
(Meyrick)
Raptorial ambush geometrid caterpillar, Eupithecia, undescribed species from Maui, feeding on Drosophila grimshawi
Oldenberg. (Photo by S. L. Montgomery.)
tera, Lepidoptera, Hymenoptera, and Diptera (only odonates
are immune). Some insect orders have a higher propensity
to evolve flightlessness resulting in genera with two or more
independently evolved flightless species.
The development of flightlessness on islands has been
considered by many to be an adaptation to extreme situations (e.g., windblown or remote insular environments), but
its relative prevalence in Hawai'i suggests that it is merely
another aspect of the adaptive radiation of our native biota
in the absence of the usual range of flightless organisms
found in continental environments.
Rather than try to explain some speciation as opportunism
in response to "vacant" niches it seems more appropriate to
consider adaptive radiation and adaptive shifts as natural processes in a complex environment full of biological opportunities. The only paradigm that seems to hold true is, If it's
possible, it will evolve. Otherwise, how could we explain
such things as the evolution of a flightless riparian nabid into
an environment already "full" of predatory spiders, shore
bugs, damselflies, dolichopodids,
and ground beetles
(Gagne 1986)?
A remarkable fact about evolution in Hawai'i is that most
of it appears to have happened in the space of a few million
years. It is probably corollary to this rapid evolution that
Hawai/i has few endemic taxa above the generic level. Species endemic to the island of Hawai'i, including most of the
Hawaiian troglobites, must necessarily be less than 700/000
years old.
14
associated
with
joinvillea
has apparently
disap-
peared along with its host plant.
Unfortunately, we may never know if the Hedylepta host
races were in fact good species or on their way to becoming
so. The early popularity of biological control to cope with
insect problems in Hawaiian plantation agriculture resulted
in the introduction of several hundred species of predatory
and parasitic insects, with little or no attention to their host
specificity or potential impact on the native biota (Howarth
1983b). Many such polyphagous species attacked native and
pest Lepidoptera indiscriminately, leading to the complete
elimination of the banana-associated Hedylepta species
(Gagne and Howarth 1984). Classical biological control
should be applied with great care in order to avert such nontarget impacts.
The Hawaiian entomofauna is a treasure chest of unstudied
evolutionary gems. Many groups remain almost untouched
by taxonomic hands. When Zimmerman wrote his classic introduction to the Insects of Hawaii in 1948, there were 85
genera that contained 10 or more endemic species. In addition to Drosophila, which we have already mentioned, the
genera with over 100 species each (number of described species in brackets) are: Hyposmocoma (350); Proterrhinus (181);
Sierola (182); Odynerus
(105); and Plagithmysus
(140).
Studies underway will add still further to this remarkable
"C1ub 100." Notable are several genera of plant bugs, family
Miridae, being revised by Wayne Gagne and crickets of the
genus Paratrigonidium
currently being monographed by
Robin Rice (UH) and associates.
Thornton et al. (1972) provided comparative data on
barklice that constitute an especially compelling demonstration of the significance of such species-rich genera. Considering the known endemic species, Micronesia has an average
of 3.4 species per genus, while Hawai'i has the phenomenal
average of 72 species per genus.
Perturbations and Fragility
Three long-held ecological tenets have been used to explain the apparent fragility of island biotas to novel pertu rbations imported from the continents: the apparent lack of
competitiveness of island species, the presence of many vacant niches, and the low number of predators.
These hypotheses concerning fragility of insular species
and ecosystems have been called into question by studies in
Hawai'i under the International Biological Program (MuellerDombois et al. 1981). Some conclusions were that island
communities are not generally characterized by a reduction
BCLLETIN OF THE ESA
in niches, that island species do not lack competitiveness
per
se, and that communities
with relatively few life forms in a
general niche may be more resistant to invasion by introduced species (because of the limited possibilities for the
subsistence of specialist herbivores and predators) (MuellerDombois and Howarth 1981).
If we look at the situations pertaining to the continents we
find extinction of species, endangered species, populations
with small geographic ranges, penetration of introduced diseases and alien plants and animals, and habitat destruction.
Fragility is common to both oceanic islands and continents.
Nevertheless, the proportion
of insular species that have
become extinct or that are currently endangered is high. This
certainly is true in Hawai'i. We need to sort out the real
differences influencing the response of insular biotas to perturbations,
including introduced
species. Island biotas may
be no more fragile than many continental ones, but they can
be accurately described as more vulnerable.
One key aspect of vulnerability
may lie in the evolutionary
history of island species. Many arise from one or a few progenitors, resulting in arrays of species with biological, behavioral, morphological,
or other commonalities.
An alien
species brought to our shores that can utilize one island insect species as prey may well exploit a whole assemblage of
its relatives.
For example,
the recently
adventive
yellowjacket, Vespula pensylvanica (Saussure), seems capable
of preying upon many of the large picture-winged
Drosophila
that lek on tree ferns in wet forests. As a result there has
been a dramatic decline in the number of individuals of many
of these Drosophila species (Carson 1982).
Another
aspect of vulnerability-the
susceptibility
of
Hawai'i's biota to endangerment and extinction-stems
from
the localized distribution
of our island species. The highly
dissected terrain with extreme rainfall and other environmental gradients over such small distances has led to many
disjunct habitats each inhabited
by many unique species.
This area effect means that any large scale environmental
alteration, for example the conversion of native habitat to
agriculture, will tend to wipe out species (Gagne 1975b).
Hawaiian land alteration began with the ancient Polynesian
settlers. They cleared large areas of lowland forest and introduced about two dozen useful plants (e.g., ti for thatching
and for wrapping foods for cooking; candlenut for oil, food,
dye, and medicine; and bananas, coconuts, and breadfruit
for food). By 1600-approximately
180 years before European
contact-perhaps
80% of all land in Hawai'i below about 450
m (1,500 ft) in elevation had been extensively altered by the
human inhabitants (Kirch 1982a,b).
Europeans introduced continentally
derived perturbations
that contributed
to the harassment of island species. These
effects are very much in evidence today. Some of the worst
offenders were and are feral pigs, goats, and sheep, seedeating rats, avian malaria-carrying
mosquitoes, and polyphagous insects such as cockroaches and ants. Agricultural crops
and ornamentals bring with them pests that also attack native
species. For example, the black twig borer, Xylosandrus compactus (Eichhoff), attacks a wide range of rare and common
native Hawaiian plants. The loss of native plants through seed
predation by rodents and introduced
insects will mean the
certain demise of associated specialist insects.
Gagne (1979, 1980) studied the distribution
of native and
introduced
insects in the '5hi'a (Metrosideros polymorpha)
and koa (Acacia koa) forest canopy on the island of Hawai'i.
He collected insects over an altitudinal transect by fogging
tree canopies with a nonpersistent
insecticide and catching
fALl. 19H4
the falling insects in large cloth funnels. The highest insect
diversity occurred in the densest forests (mixed-species forests and '5hi'a rain forests). Average insect and spider biomass and diversity were uniformly
high at mid elevations,
low at low elevations (below about 600m [2,000 ft]), and low
at high elevations. The low diversity found at high elevations
was likely due to the prevalence of open canopy forests (i.e.,
with less productivity).
Also, introduced temperate insects,
preadapted to cooler forests, and feral ungulates may have
depressed diversity. The paucity of insects at lower elevations correlated with the increasing prevalence of alien predatory ants; low elevation samples had few native species and
were composed largely of ants and cockroaches.
When novel perturbations
are moderated or eliminated,
native species generally do rebound, if not already driven to
extinction (Mueller-Dombois
and Howarth 1981). But native
insects have been facing an assault by alien biota and land
abuses that might similarly endanger an array of continental
communities.
Importation
and establishment
of alien species continues
largely unabated. Horticulturalists
and other exotic-plant fanciers bring flora from all corners of the globe. Over 4.3 million tourists visit Hawai'i each year, and relaxed inspection
of baggage allows the entrance of pests. This, in combination
with other sources, is responsible for the inadvertent
importation and establishment of over two dozen alien insects
Thread-legged
bugs.
scribed species. Bottom:
arid Howarth (holotype
cave). (Photos by W. P.
Top: Epigean Nesidiolestes,
undeTroglobitic Nesidiolestes ana Gagne
and allotype in copulo on roof of
Mull.)
15
Flightless brown lacewing, Pseudopsectra
merman (Hemerobiidae)
by S. L. Montgomery.)
swezeyi Zimon rain forest floor of Kaua' i. (Photo
deavors are essential for the continued survival of our native
entomofauna.
An essential base for the prevention of biotic destruction
is an inventory of what is present and, as indicated above,
the entomological
survey of Hawai'i is far from complete.
The Department of Entomology at the Bishop Museum has
Pacific-wide emphasis in one of the several largest collections
in the U.S., recently named the J. Linsley Gressitt Center for
Research in Entomology.
However, we recognize a special
responsibility
to survey the arthropods of Hawai'i. There has
been a resurgence of survey activity in the state over the past
15 years, involving UH, State Department of Agriculture, and
others, as well as BPBM. There has also been considerable
increase in fieldwork
and systematic studies by entomologists from overseas. The Hawaiian entomofauna offers unlimited possibilities for ecological, evolutionary,
and systematic
studies. As Zimmerman (1948a) did in his introduction
to the
Insects of Hawaii, we encourage any and all interested to
take advantage of the exciting natural laboratory of Hawai'i.
References Cited
each year (Beardsley 1979). An additional dozen per year are
brought in for biological control purposes (Davis and Chong
1968).
Entomologists
have a responsibility
to speak and act on
behalf of insect "clientele,"
and must join with other conservationists to protect native habitats and to help prevent
disturbances and eliminate or ameliorate existing ones. Need
it be said that this is not a position contrary to "applied"
themes? Essentially all of the classes of perturbations
that
adversely affect the native biota have immediate or predictable negative influences on human health and economy; for
example, the introduced
species with agricultural or public
health significance, the destruction of watershed and disruption of ecosystems by feral ungulates, and so on.
The proposed
"tri-fly
eradication
program,"
directed
against three species of introduced pestiferous tephritids in
Hawai'i (a fourth species has recently become established)
and now being reviewed for its environmental
impact, is a
case in point.
It has been argued that the poison baitspraying and other measures included in the program design
will have a dire effect on the endemic entomofauna,
as well
as on other invertebrates
and on forest birds (through the
food chain). However, we expect that the decision whether
to proceed with this program will be based on evaluation of
chance of success, cost/benefit analysis, alternative defense
lines to protect crops in the continental United States, negative impact on other crops, disruption
of intrastate travel
and commerce, and so on.
There is some cause for optimism about the survival of the
native entomofauna.
Enthusiasm and important background
information
have been generated by a history of productive
research, such as the projects associated with the Island Ecosystems Subprogram of the International
Biological Program
(1970-1975) and the 21-year old Hawaiian Drosophila project
discussed earlier. In 1983, the Hawaiian Evolutionary Biology
Program was established
at the University of Hawai'i and
promises to be the progenitor of a long-overdue institute for
the study of Hawaiian terrestrial evolutionary
biology.
The Nature Conservancy of Hawai'i, the National Park Service, the Hawaiian Islands National Wildlife Refuges, and the
State Natural Area Reserves System designation and protection of native habitats represent positive steps. Such en16
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•
CHRISSIMON(top left) is a research associate both at the
Bishop Museum and the University of Hawaii. Her interests center on evolution, systematics, and ecology. She
has studied periodical cicadas for 10 years and is beginning a project on Hawaiian Drosophila. She is an active
participant in the Hawaiian Evolutionary Biology Program
and the Organization for Tropical Studies. WAYNEGAGNE
(top right) is an entomologist at the Bishop Museum. His
research interests encompass biosystematics of Pacific
Basin Heteroptera, especially Miridae; conservation,
especially of terrestrial arthropods of the Hawaiian Islands, entomology of subsistence agriculture and permacultural agroforestry, and canopy-associated arthropods of rain forests. FRANCIS
HOWARTH
(bottom left) is curator of the Hawaiian Insect Collection at Bishop Museum.
He has a deep research interest in the evolution and
ecology of cave animals, as well as in island ecology, biogeography, and biosystematics of the Ceratopogonidae.
FRANKRADOVSKY
(bottom right) has been chairman of the
Department of Entomology at the Bishop Museum for the
past 12 years. Medical entomology and acarology are his
areas of specialization, but he has found that one cannot
live in Hawai'i without having broader entomofaunal interests.
17