Download Insect Orders II: Polyneoptera (cont`d)

Insect Orders II: Polyneoptera (cont’d)
•  The Polyneoptera consists of 11 extant orders. All
orders except the Plecoptera have terrestrial
wingless immature stages that resemble the adult
stage (paurometabolous development). The
Plecoptera have aquatic nymphs that do not
resemble the adult stage (hemimetabolous
development).
•  Sister group relationships in the Polyneoptera are
still unresolved in many respects, largely do to the
lack of a sufficient number of derived characters
shared among the members (synapomorphies).
•  The order Orthoptera is by far the most diverse order
in the Polyneoptera, followed by the Dictyopteran
orders. At least two orders, the Grylloblattodea and
the Mantophasmatodea appear to relicit groups,
widely distributed but of low diversity.
•  The Zoraptera is a particularly difficult order to place
phylogenetically, but it now appears to the sister
group of the Embiidina.
Phasmatodea (Stick and leaf insects)
•  Classification. More than 3000 species segregated
into 4 families. Higher classification is unclear and
subject to debate, as are the sister group relationships
of walking sticks.
•  Structure. Elongate body, some times very large (>50
cm in one species from Borneo). Antennae are short
to very long and slender. Wings much reduced or
absent in many species. Body segments in some
species elaborated with spines, flanges and other
processes that aid in crypsis or in direct defense
against predators. Possession of anterior dorsolateral
defensive gland on the prothorax. Eggs have an
operculum (lid) and are elaborately sculptured.
•  Natural history. Most species are slow moving
herbivores commonly found on vegetation. Walking
sticks defend themselves from predators through
crypsis or release of defensive chemicals. Many
species orient their bodies parallel to their perch and
slowly sway back and forth if disturbed. This
movement presumably mimics vegetation caught in
the wind. Walking sticks can regenerate limbs, which
is uncommon in insects. Males mate with females by
mounting on their back and rotating their abdomen
through 180o during copulation. Many species are
parthenogenetic. Eggs are scatter from high
vegetation and apparently mimic plant seeds. Eggs of
some species are picked up by ants and tended in ant
nests until they hatch.
Wing loss and recovery in stick insects
In 2003 Michael Whiting of BYU
and colleagues published a
paper that argued that wings in
walking sticks were lost and
recovered several times
independently.
Orthoptera (Crickets, katydids, wetas,
grasshoppers and kin)
•  Classification. Over 20,000 species divided into two
suborders: the Ensifera (true crickets, Mormon crickets,
long-horned crickets, Jerusalam crickets and katydids), and
the Caelifera (short-horned grasshoppers, lubber
grasshoppers, slant-faced grasshoppers, and pygmy mole
crickets). The Ensifera consists of 10,000 species in 10
families and first appeared in the late Permian (250 mya).
The Caelifera consists of about 11,000 species in 20
families and first appeared in the Triassic (240 mya)
•  Structure. A famous orthopteran apomorphy is the
possession of saltatorial hind legs. Ensifera have long
flagellate antennae, Caelifera have reduced antennae. All
species have chewing mouthparts. Ovipositor is long in the
Ensifera and short in the Caelifera. Some species with
highly modified body form are obligate nest associates of
ants. Many species have specialized structures for
acoustical communication.
•  Natural history. Most species are phytophagous, but
some species of Ensifera (Tettigoniidae) are predaceous.
Caelifera are active during daylight and Ensifera are
usually active at night. Orthopterans defend themselves
from predators through crypsis, spines on their legs and
bodies, or toxic chemicals and aposomatic coloration.
Some species of Caelifera are deadly. A number of species
are migratory over long distances and during outbreaks can
cause devastating agricultural damage (e.g., the desert
locust, the migratory locust and the Mormon cricket).
Acoustic communication in the Orthoptera
•  Orthopterans are the most vocal of all insect
orders, with calling behavior playing a major
role in the biology and evolution of the order.
Acoustic signals are used in courtship,
mating and male-male competition for
mates. Songs are often species-specific.
•  In the Ensifera acoustical signals are
produced by rubbing a specialized area of
the right forewing across a corresponding
area of the left forewing. The rasping sound
created by the file and scrapper on the
wings is amplified by specialized
membranes on the wings called “mirrors”.
Sound reception occurs through forewardfacing tympanal membranes located on the
tibae of the forelegs.
•  In the Caelifera acoustical signals are
produced by scrapping the hind legs against
stiff edges of the forewings. Sound reception
is accomplished by tympanal membranes on
the abdomen.
•  Males in one relicit family of Caelifera
(Cylindrachetids) produces their song by
rubbing their mandibles together. Another
goup of Caelifera make cone-shaped
“amphitheaters” at the opening of their
subterranean tunnels to amplify their calls.
Cylindrachetid File on cricket
forewing
Foretibial tympanum
of cricket
Drum-like mirror on
fossil cricket forewing
Dictyoptera
•  The Dictyoptera comprise the last 3 orders
in the Orthopteroid (Polyneopteran)
complex: the Blattaria (cockroaches),
Isoptera (termites) and Mantodea
(mantises).
•  Relationships among these 3 orders is
much debated and much of the debate is
caused by the common assumption that
all three orders are monophyletic.
•  Modern understanding of the relationships
among these three groups is derived from
three character system, the proventriculus,
male genitalia and the vestigial ovipositor.
The deposition of the eggs in the form of
an ootheca is also a groundplan feature of
the Dictyoptera.
Oothecae
•  Recent evidence indicates that the
Blattaria is the sister group of the
Mantodae and that the Isoptera are
embedded in the Blattaria, making the
Blattaria paraphyletic as currently defined.
Proventriculus
Blattaria (Roaches)
•  Classification. 4000 described species in 460
genera. Family-level classification is unsettled, but
centers around 6. Phylogenetic relationships
among these families is also debated. The position
of the genus Cryptocercus is of particular interest
in its relationship to termites.
•  Structure. Body in all species is dorso-ventrally
flatten with a shield-like pronotum that covers the
head. Forewings form overlapping tegmina. Eggs
are enclosed in a capsule called an ootheca.
•  Natural history. Most species are nocturnal. The
small minority that are active during daylight are
brightly colored. Most species are terrestrial, with a
few species primarily arboreal. Some species are
obligate nest associates of ants. Most species are
omnivorous. Species in the genus Cryptocercus
feed on wood with the aid of symbiotic gut protists.
These symbionts are lost during each molting cycle
and individuals must be re-inoculated. Species of
Cryptocercus live in kin groups that facilitate the reinoculation process. Behavior superficially similar
to termites.
Isoptera (Termites)
•  Classification. 2900 species divided into 7 families, with over
80% of the species belonging to the “higher” termite
family,Termitidae. The Isoptera is the only major insect order
without an extinct family. Termites arose in the Late Jurassic
(150 mya) or Early Cretaceous (140 mya), relatively late
compared to other polyneopteran orders.
•  Structure. Adult termites are polymorphic in body form and
function. These different body forms are called castes. Three
different adult castes exist in termite colonies: 1) winged
primary reproductives, 2) wingless soldiers, and 3) wingless
workers. The soldier caste can be distinguished from the
worker caste by its highly modified head. A fourth caste, the
supplementary reproductives, is sometimes present and is
distinguished from the primary reproductive caste by the
absence of functional wings. Structure and function of the
soldier caste is highly variable among species. Two broad
categories of soldiers exist, those with well developed
mandibles (mandibulate soldiers) and those with reduced
mandibles and a highly modified frontalis (nasute soldiers).
•  Natural history. All termite species are eusocial, meaning that
colony members come from two or more generations and that
there is reproductive division of labor among individuals.
Soldiers are behaviorally specialized as nest defenders.
Workers perform most of the day-to-day tasks, including nest
maintenance and foraging. Reproductive castes are egg-laying
machines, who abdomens can become grotesquely enlarged
(physogastric) as it fills with eggs. All termite species live in
nests, some of which can be very elaborate. Termite species
are phytophagous or fungivorous and rely on specialized
symbiotic protists to aid in the digestion of cellulose. Termites
are host to many arthropods that are obligately or facultatively
dependent on termite nests for food and shelter. These
organisms are called termitophiles.
Termite castes
Soldier heads
Evolution of Termites
•  Recent phylogenetic evidence indicate that the sister group
of the termites is the wood-eating roach Cryptocercus.
•  Kin groups of wood roaches consisting of a pair of parents
and about 20 offspring inhabit galleries in a log and they
remain together for at least 3 years. The nymph superficially
resembles termites (small, pale and blind) and take
approximately 6 years to mature.
•  Nymphs feed on liquids exuded from the anus of adults for
their first year (proctodeal trophallaxis), which allows them to
acquire mutualistic protists that are required for the digestion
of wood. Nymphs must reacquire these protists after each
molt.
•  Cryptocercus shares with two families of lower termites
several genera of distinctive protists. Earlier experiments
have shown that protists extracted from the hindgut of
Cryptocercus can be successfully transferred into the
sterilized hindgut of termites.
•  Wood roaches and especially termites harbor a remarkable
diversity of protists in their hindgut, including bacteria,
methane-producing archaebacteria, spirochetes, numerous
protists in a variety of families, and a very basal lineage of
eurkaryotes, the Parabasalea.
•  Unlike wood roaches, termites have a huge ecological
impact on their environment. Termites are estimated to
produce 2-5% of global methane (a greenhouse gas). They
are also instrumental in soil mineralization and humification.
In Africa they consume up to 20% of the available plant
biomass.
Trichonympha is a flagellate protozoan that lives in
the hindgut of Cryptocercus and lower termites.
Mantodea (Mantises)
•  Classification. 2300 species divided into 434 genera and 8
families. Only one family, the Mantidae, in found in the US.
•  Structure. Most distinctive features are the elongated
prothorax and forelegs highly modified into raptorial
appendages used for catching prey. Eyes are large and
bulging with a large frontal field and fovea, giving mantises
excellent binocular vision. Head is freely movable and used
to track and focus on moving prey. Head is hypognathous,
but can be moved into the prognathous position when
attacking and eating prey. More derived groups of mantises
have a unique cyclopean “ear” located on the meta-thorax
between the sternites and just anterior to the hind coxae.
This ear is tuned to the ultrasound frequencies of
insectivorous bats.
•  Natural history. Mantises are highly predaceous insects.
They are excellent sit-and-wait predators usually found
perched on vegetation. Many species employed elaborate
cryptic coloration to facilitate camouflage from both
predators and prey, sometimes termed aggressive
mimicry. Some of the larger species are able to catch and
eat small lizards and frogs. Males copulate with females by
mounting on their backs (unique in the Dictyoptera), which
is thought to be an adaptation to avoid being eaten by the
females. Males can execute copulatory movements for up
to 20 hr after decapitation, which suggests that
consumption by their mates is not uncommon. In threequarters of the species whose mating has been observed,
over 50% of the natural prey items of females were males.