Strepsiptera

Taxobox
name = Strepsiptera
fossil_range=Middle Cretaceous - Recent


image_caption = male


regnum = Animalia
phylum = Arthropoda
classis = Insecta
ordo = Strepsiptera
ordo_authority = Kirby, 1813
subdivision_ranks = Families
subdivision =
Mengenillidae
Mengeidae
Stylopidae
Bohartillidae
Corioxenidae
Halictophagidae
Callipharixenidae
Elenchidae
Myrmecolacidae

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.Whiting, M. F in Resh, V. H. & R. T. Cardé (Editors) 2003. Encyclopedia of Insects. Academic Press. pp. 1094-1096]

Appearance and biology

Male Strepsiptera have wings, legs, eyes, and antennae, and look like flies, though they generally have no useful mouthparts. Many of their mouth parts are modified into sensory structures. Adult males are very short-lived (usually less than five hours) and do not feed. Females, in all families except the Mengenillidae, never leave their hosts and are neotenic in form, lacking wings and legs. 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 emerge from the brood opening on the head, which protrudes outside the host body. These larvae have legs (which lack trochanters) and actively search out new hosts.Borror, D.J., Triplehorn, C.A. Johnson. ( 1989) Introduction to the Study of Insects. 6th ed. Brooks Cole.] 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. clade| style=font-size:75%;line-height:75%
label1=Neoptera
1=clade
1=clade
1=clade
1=Megaloptera
2=Raphidioptera
3=Neuroptera
2=Coleoptera
label2=?
2=clade
label1=Strepsiptera
1=clade
1=Stylopidia
2=?Mengenillidae
3=clade
1=clade
1=clade
1=Diptera
2=Mecoptera
3=Siphonaptera
2=clade
1=Trichoptera
2=Lepidoptera
2=Hymenoptera Suggested phylogenetic position of the Strepsiptera. [Kathirithamby, Jeyaraney. 2002. Strepsiptera. Twisted-wing parasites. Version 24 September 2002. [http://tolweb.org/Strepsiptera/8222/] in [http://tolweb.org/ The Tree of Life Web Project] ] 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). [Kathirithamby, Jeyaraney (2001) Stand Tall and They Still Get You in Your Achilles Foot-Pad. Proceedings: Biological Sciences. 268(1483):2287-2289.] 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. [Kathirithamby, Jeyaraney; Larry D. Ross; J. Spencer Johnston (2003) Masquerading as Self? Endoparasitic Strepsiptera (Insecta) Enclose Themselves in Host-Derived Epidermal Bag. Proceedings of the National Academy of Sciences of the United States of America. 100(13):7655-7659.] Male larvae produce pupae after the last moult, but females directly become neotenous adults. [Beani, Laura (2006) Crazy wasps: when parasites manipulate the "Polistes" phenotype. Ann. Zool. Fennici 43:564-574 [http://www.sekj.org/PDF/anz43-free/anz43-564.pdf PDF] ] 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. [Buschbeck,E. K.,B. Ehmer, R. R. Hoy (2003) The unusual visual system of the Strepsiptera: external eye and neuropils. J. Comp. Physiol. A 189:617–630 DOI 10.1007/s00359-003-0443-x [http://hoylab.cornell.edu/hoy/buschbeck_ehmer_hoy2003.pdf PDF] ]

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. [Wojcik, Daniel P. (1989) Behavioral Interactions between Ants and Their Parasites. The Florida Entomologist. 72(1):43-51.]

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; however later research suggested their inclusion as a sister group to the flies, in a clade called the "halteria" [Michael F. Whiting (1998) Long-Branch Distraction and the Strepsiptera. Systematic Biology 47(1):134-138. [http://whitinglab.byu.edu/PDF/longbranchstrep.pdf PDF] ] which have one pair of the wings modified into halteres.Whiting, Michael F.; James C. Carpenter; Quentin D. Wheeler; Ward C. Wheeler (1997) The Stresiptera Problem: Phylogeny of the Holometabolous Insect Orders Inferred from 18S and 28S Ribosomal DNA Sequences and Morphology. Systematic Biology. 46(1):1-68. ] 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. [Bonneton, F.; F. G. Brunet; J. Kathirithamby and V. Laudet (2006) The rapid divergence of the ecdysone receptor is a synapomorphy for Mecopterida that clarifies the Strepsiptera problem. Insect Molecular Biology 15(3):351-362.] Study of their evolutionary position has been problematic due to difficulties in phylogenetic analysis arising from long branch attraction. [Huelsenbeck, John P. (1998) Systematic Bias in Phylogenetic Analysis: Is the Strepsiptera Problem Solved? Systematic Biology. 47(3):519-537.] 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 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.

ee also

* Entomophagous parasite

Notes

References

*cite book|author=Grimaldi, D. and Engel, M.S. |title=Evolution of the Insects|year=2005|publisher=Cambridge University Press|id=ISBN 0-521-82149-5

External links

* http://tolweb.org/tree?group=Strepsiptera
* [http://www.gbhap.com/journals/pdf/ghbi_12_01_06.pdf Survey of Modern Counterparts of Schizochroal Trilobite Eyes: Structural and Functional Similarities and Differences]
* [http://www.cals.ncsu.edu/course/ent425/compendium/streps~1.html Family outline: Strepsiptera]