The Strepsiptera (known in older literature as twisted-winged parasites) are an order of insects with nine families making up about 600 species. The early stage larvae and the short-lived adult males are free-living but most of their life is spent as endoparasites in other insects such as bees, wasps, leafhoppers, silverfish, and cockroaches.
|2=|3=|2=Hymenoptera}} }} }} Suggested phylogenetic position of the Strepsiptera. Strepsiptera find and enter their insect hosts as planidium larvae. These first-instar larvae have stemmata (simple, single-lens eyes) and they enter their hosts by secreting enzymes that soften the cuticle, usually in the abdominal region of the host. Some species have been reported to enter the eggs of hosts. Larvae of Stichotrema dallatorreanurn Hofeneder from Papua New Guinea were found to enter their orthopteran host's tarsus (foot). Once inside the host, they undergo hypermetamorphosis and become a less mobile legless larval form. They induce the host to produce a bag like structure inside which they feed and grow. This structure, made from host tissue, protects them from the immune defences of the host. Larvae go through four more instars and in each moult there is separation of the older cuticle but no discarding ("apolysis without ecdysis") leading to multiple layers being formed around the larvae. Male larvae produce pupae after the last moult, but females directly become neotenous adults. 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 with a large lens and capable of producing a partial image, 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 rarely seen. They may sometimes be seen at light traps or may be lured using cages containing virgin females.
Strepsiptera may alter the behaviour of their hosts. Myrmecolacids may cause their ant hosts to climb up the tips of grass leaves, possibly to increase the spread of female pheromones to increase the chances of being located by males.
ClassificationThe 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; however later research suggested their inclusion as a sister group to the flies, in a clade called the halteria which have one pair of the wings modified into halteres. Molecular evidence fails to support their position as a sister-group of the beetles. Later molecular studies suggest that they are outside the clade Mecopterida containing the Diptera and Lepidoptera however there is no strong evidence for affinity with any other extant group. Study of their evolutionary position has been problematic due to difficulties in phylogenetic analysis arising from long branch attraction. The oldest known strepsipteran is Cretostylops engeli discovered in middle Cretaceous amber from Myanmar.
FamiliesThe 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 having 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 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.
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