AY Honors/Insect/Strepsiptera

The Strepsiptera (known in older literature as twisted-winged parasites) are an order of insects with nine families making up about 600 species. They are obligate endoparasites on other insects; their hosts include bees, wasps, leafhoppers, silverfish, and cockroaches.

Appearance and biology

Male Strepsiptera have wings, legs, eyes, and antennae, and look like flies, though they generally have no useful mouthparts. Females, in all families except the Mengenillidae, never leave their host and are neotenic in form, lacking wings and legs. Males have a very short adult lifetime (usually less than five hours) and do not feed as adults. Many of their mouth parts are modified into sensory structures. Virgin females release a pheromone which the males search for. In the Stylopidia the female has its anterior region extruding out of the host body and the male mates by rupturing the female's brood canal opening which lies between the head and prothorax. Sperm passes through the opening in a process termed hypodermic insemination. Each female produces many thousands of triungulin larvae that escape from its body and out of the host into the soil and vegetation. These actively search out new hosts. Their hosts include members belonging to the orders Zygentoma, Orthoptera, Blattodea, Mantodea, Heteroptera, Hymenoptera, and Diptera. In the Strepsipteran family Myrmecolacidae, the males parasitize ants while the females parasitize Orthoptera. Template:Userboxtop Template:Clade Suggested phylogenetic position of the Strepsiptera. Template:Userboxbottom Strepsiptera find and enter their insect hosts as planidium larvae. The first instar larvae have stemmata (simple, single-lens eyes). They undergo hypermetamorphosis and become a less mobile legless larval form. In this stage they feed within the host's body cavity. The colour and shape of the host's abdomen may be changed and the host usually becomes sterile. The parasites then undergo holometabolous metamorphosis to become adults. Adult males emerge out of the host body while females stay inside. Females may occupy up to 90% of the abdominal volume of their hosts.

Male Strepsiptera have eyes unlike those of any other insect, resembling the schizochroal eyes found in the trilobite group known as Phacopida. Instead of a compound eye consisting of hundreds of ommatidia, each of which sees one pixel, the strepsipteran eyes consist of only a few dozen ommatidia separated by cuticle and/or setae, giving the eye a blackberry-like appearance.

Multiple females may be seen within a stylopized host. Males are extremely rare. They may sometimes be seen at light traps or may be lured using cages containing virgin females.

Classification

The order, named by William Kirby in 1813, is named for the hind wings (strepsi=twisted + ptera=wing), which are held at a twisted angle when at rest. The forewings are reduced to halteres (and initially thought to be dried and twisted).

Strepsiptera are an enigma to taxonomists. Originally it was believed they were the sister group to the beetle families Meloidae and Ripiphoridae, which have similar parasitic development and forewing reduction; more recent theories say they are the sister group to the beetles; even more recently, molecular genetic analyses have suggested that they are the sister group to the flies, which have hindwings modified into halteres. The oldest known strepsipteran is Cretostylops engeli discovered in middle Cretaceous amber from Myanmar.

Families

The Strepsiptera have two major groups Stylopidia and Mengenillidia. The Mengenillidia include the extinct family Mengeidae and one extant family Mengenillidae. They are considered more primitive and the females are free living, with rudimentary legs and antennae. The females have a single genital opening. The males have strong mandibles.

The other group, Stylopidia, includes seven families Corioxenidae, Halictophagidae, Callipharixenidae, Bohartillidae, Elenchidae, Myrmecolacidae, and Stylopidae. All Stylopidia have endoparasitic females which have multiple genital openings.

Stylopidae have 4 segmented tarsi and 4-6 segmented antennae with the third segment having a lateral process. The family Stylopidae may be paraphyletic. The Elenchidae have 2-segmented tarsi and 4 segmented antennae with the third segment having a lateral process. The Halictophagidae have 3-segmented tarsi and 7-segmented antennae with lateral processes from the the third and fourth segments. The Stylopidae mostly parasitize wasps and bees, the Elenchidae are known to parasitize Fulgoroidea while the Halictophagidae are found on leafhoppers, treehoppers as well as mole cricket hosts.

References

• Grimaldi, D. and Engel, M.S. (2005). Evolution of the Insects. Cambridge University Press. ISBN 0-521-82149-5.

External links

• http://tolweb.org/tree?group=Strepsiptera
• Survey of Modern Counterparts of Schizochroal Trilobite Eyes: Structural and Functional Similarities and Differences