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 180 o 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.