Strepsiptera

(invertebrate zoology) An order of the Coleoptera that is coextensive with the family Stylopidae.

(Strepsipterans)

Class: Insecta

Order: Strepsiptera

Number of families: 9

Evolution and systematics

The Strepsiptera are thought to have originated in the Carboniferous, but the earliest known fossils are from the lower Cretaceous amber of Lebanon. The phylogenetic position of the strepsipterans is unclear, with four possible phylogenetic placements. The first is as the sister group of the beetle family Rhipiphoridae (Coleoptera), which has similar parasitic development, flabellate (branched) antennae, and forewing reduction. The second is as the sister group of beetles (Coleoptera), because they use only the hind wings for flight. The third possible placement is as the sister group of flies (Diptera), which have hind wing halteres (front wing and hind wing halteres could have switched places by a homeotic mutation) and similarities in their DNA. Fourth, they may be placed outside the endopterygote insects, such as beetles and flies, because the pupal stage is preceded by two pharate larval instars (enclosed within the skin of a previous instar), with external wing buds in females, and larval eyes are carried over to the adult stage. The more than 500 described species of strepsipterans are classified in two suborders: Mengenillidia, with two families (one, Mengeidae, known only from fossil males in Eocene Baltic amber), and Stylopidia, with seven families.

Physical characteristics

Strepsipterans have two different morphologies ("hypermetamorphosis"). The first larval instar, called the triungulinid, is free-living and actively host-seeking, and has simple eyes, legs, and two long caudal setae. The second through the last instar larvae (they can have 4 to 7 instars depending on the species) are maggot-like and endoparasitic. Adult males usually are 0.04–0.12 in (1–3 mm) long, with some reaching 0.3 in (7 mm). Females typically are 0.19 in (5 mm) long, but they can range from 0.08 to 1.18 in (2–30 mm). There is extreme sexual dimorphism: adult males look like insects, whereas females look like larvae (larviform) and lack legs, antennae, and external genitalia. Adult males are free living, whereas most females are internal parasites on other insects and remain in the host for their entire lives. Females of the family Mengenillidae are free living.

Males have berry-like eyes, with each lens separated by cuticle or setae; branched antennae; nonfunctional mouthparts; reduced forewings in the form of halteres used for balancing during flight; fan-shaped hind wings with longitudinal veins but no cross veins; and no cerci. Strepsipterans also are called "twisted wing parasites," referring to the peculiar twisted shape of the male hind wings in flight. In the suborder Stylopidia the female head and thorax are united to form a cephalothorax, which protrudes from the body of the host. The female lives within the last larval skin, in which she also pupates, and her whole abdominal cavity is filled with eggs or developing embryos.

Distribution

Although the order is cosmopolitan, most species occur in the tropics.

Habitat

Strepsipterans are found wherever their hosts live. Known hosts include Lepismatidae (Thysanura), Blattidae (Blattodea), Mantidae (Mantodea), Gryllidae, Gryllotalpidae, Tettigoniidae (Orthoptera, Ensifera), Tridactylidae (Orthoptera, Caelifera), Psyllidae (Hemiptera, Sternorrhyncha), Cercopidae, Cicadellidae, Membracidae, Delphacidae, Dictyopharidae, Eurybrachidae, Ricaniidae, Flatidae, Fulgoridae, Issidae, Tettigometridae (Hemiptera, Auchenorrhyncha), Coreidae, Cydnidae, Lygaeidae, Pentatomidae, Scutelleridae (Hemiptera, Heteroptera), Tephritidae, Platysomatidae (Diptera), Formicidae, Vespidae, Sphecidae, Colletidae, Halictidae, and Andrenidae (Hymenoptera).

Behavior

The life cycles of strepsipterans are complex. Eggs are retained within the body of the female until they hatch. The triungulins leave the body of the mother's host and wait for another host. They jump or crawl onto the new host and are transported back to its nest, where they penetrate the host's eggs or developing larvae. The second instar larvae live and feed inside the host's body cavity. Larvae molt four to seven times and reach the last instar at about the same time that the host is ready to pupate. The larvae pupate with their heads and thoraxes protruding between the host's fourth and fifth abdominal segments.

Males use an eversible saclike structure on the head (similar to the ptilinum of some flies) to open the puparium, and leave the host while it is flying; they have only a few hours to find females and mate before dying. Females of the suborder Stylopidia remain in the puparium, protruding from the host for their entire lives, their life spans directly linked to those of their hosts. In the Mengenillidae both sexes abandon the host to pupate externally, and the adults are free living.

Feeding ecology and diet

Parasitic larvae of the second through the last instar and Stylopidia females feed by filtering the host blood; free-living adults do not feed.

Reproductive biology

Female strepsipterans attract males with pheromones. Males fertilize females by injecting sperm into the female's body cavity. Females are sexually mature before molting to the adult stage and give birth to live larvae instead of laying eggs. In some species females are parthenogenetic, reproducing without being fertilized by a male.

Conservation status

No strepsipteran is cited by the IUCN.

Significance to humans

Strepsipterans are not very common, and few people other than entomologists are likely to see them. Although strepsipterans do not kill their hosts, they greatly reduce their nutriment intake; "stylopized" (parasitized by strepsipterans) insects generally are sterile, having been effectively castrated by their parasites. Thus, strepsipterans probably are indirectly beneficial to humans, because they may control population levels of economically important insects. Such insects include Antestia stinkbugs (Hemiptera, Pentatomidae) that attack coffee plantations; fruit flies (Diptera, Tephritidae); long-horned grasshoppers (Orthoptera, Tettigonidae), which defoliate oil palms and coconuts; virus-transmitting leafhoppers (Hemiptera, Cicadellidae), for example, Perkinsiella vitiensis on sugarcane and Nephotettix species on rice; and plant hoppers (Hemiptera, Delphacidae), such as Nilaparvata lugens and Sogatella furcifera on rice.

Species accounts

Resources

Carvalho, E. Luna de., and M. Kogan. "Order Strepsiptera." In Immature Insects, Vol. 2, edited by F. W. Stehr. Dubuque, IA: Kendall/Hunt Publishing, 1991.

Kathirithamby, J. "Strepsiptera." In The Insects of Australia: A Textbook for Students and Research Workers, Vol. 2, edited by I.D. Naumann, P. B. Carne, J. F. Lawrence, et al. 2nd edition. Carlton, Australia: Melbourne University Press, 1991. ——. "Strepsiptera of Panama and Mesoamerica." In Insects of Panama and Mesoamerica, edited by D. Quintero and A. Aiello. New York: Oxford University Press, 1992.

Bohart, R. M. "A Revision of the Strepsiptera with Special Reference to the Species of North America." California University Publications in Entomology 7, no. 6 (1941): 91–160.

Kathirithamby, J. "Review of the Order Strepsiptera." Systematic Entomology 14 (1989): 41–92.

Kinzelbach, R. K. "The Systematic Position of the Strepsiptera (Insecta)." American Entomologist 36 (1990): 292–303.

Whiting, M. F. "Phylogenetic Position of the Strepsiptera: Review of Molecular and Morphological Evidence." International Journal of Insect Morphology and Embryology 27 (1998): 53–60.

Pohl, Hans. "Strepsiptera: Twisted-Wing Parasites." 5 Mar. 2002. [7 May 2003] . "Strepsiptera: Biology, Genomics, Natural History, and Phylogeny." [7 May 2003] .

Tree of Life Web Project. "Strepsiptera: Twisted-Wing Parasites." [7 May 2003] .

[Article by: Natalia von Ellenrieder, PhD]

An order of twisted-wing insects that spend most of their life cycle as internal parasitoids of other insects. The adult male is only a few millimeters in wing span, is free living, and has only one pair of full flight wings (the posterior, or metathoracic, pair). The front (mesothoracic) wings are reduced to narrow, clublike organs that may function as halteres, or flight balancers. The male eyes are coarsely faceted and berrylike, and the antennae have four to seven segments, with some segments having finger- or bladelike extensions. Most adult females are immobile, blind, and larviform, and live inside the insect host. Rarely, the female is free living, with legs and eyes but no wings. More than 600 species of Strepsiptera are known, many of them not yet formally described and named. The order's relationship to other insect orders remains uncertain.

Both male and female begin larval life as mobile first-stage organisms with eyes and three pairs of functional legs. These triunguloids eventually attack the immature or adult forms of the host and enter their bodies, where they molt to an apodous instar. Two subsequent molts result in the divergence of the sexes and the differentiation of a hardened forebody that eventually protrudes through the host integument; the molted larval integuments are not shed but are incorporated in the general puparial wall arid the neotenous adult female capsule. Males (and some adult females) emerge from the puparium and begin the search for a mate, probably through the mediation of airborne pheromones.

Strepsiptera are found worldwide in temperate and tropical habitats. They parasitize insects, mostly of orders Hemiptera and Hymenoptera, but also some cockroaches, mantids, orthopterans, flies, and silverfish. Their effect on the host is variable, ranging from reproductive failure to death. See also Endopterygota; Pheromone.

Strepsiptera Fossil range: 125–0 Ma PreЄ Є O S D C P T J K Pg N Middle Cretaceous - Recent
male
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Class: Insecta Order: Strepsiptera Kirby, 1813
Families
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.^[1]

Contents 1 Appearance and biology 2 Classification 2.1 Families 3 See also 4 Notes 5 References 6 External links

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.^[1] 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.^[2] 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.^[1]

Neoptera Megaloptera Raphidioptera Neuroptera Coleoptera  ? Strepsiptera Stylopidia ?Mengenillidae Diptera Mecoptera Siphonaptera Trichoptera Lepidoptera Hymenoptera Suggested phylogenetic position of the Strepsiptera.[3]

Strepsiptera eggs hatch inside the female and the planidium larvae can move around freely within the female's haemocoel, which is unique to these animals. The female has a brood canal that communicates with the outside world and it is through this the larvae escape.^[4] The larvae are very active, as they only have a limited amount of time to find a host before they exhaust their food reserves. These first-instar larvae have stemmata (simple, single-lens eyes) and once they latch onto a host they enter it 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).^[5] 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.^[6] Male larvae produce pupae after the last moult, but females directly become neotenous adults.^[7][8] 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.^[1]

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.^[1][9]

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.^[1]

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.^[10]

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; early molecular research suggested their inclusion as a sister group to the flies,^[1] in a clade called the halteria^[11] which have one pair of the wings modified into halteres^[12], and failed to support their relationship to the beetles.^[12] More recent molecular studies, however, suggest that they are outside the clade Mecopterida (containing the Diptera and Lepidoptera), yet there is no strong evidence for affinity with any other extant group.^[13] Study of their evolutionary position has been problematic due to difficulties in phylogenetic analysis arising from long branch attraction.^[14] 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.^[1]

The other group, Stylopidia, includes seven families Corioxenidae, Halictophagidae, Callipharixenidae, Bohartillidae, Elenchidae, Myrmecolacidae, and Stylopidae. All Stylopidia have endoparasitic females having multiple genital openings.^[1]

Stylopidae have 4 segmented tarsi and 4-6 segmented antennae with the third segment having a lateral process. The family Stylopidae may be paraphyletic.^[1] 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.^[2] 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.^[2]

See also

• Entomophagous parasite

Notes

1. ^ ^{a b c d e f g h i j} Whiting, M. F in Resh, V. H. & R. T. Cardé (Editors) 2003. Encyclopedia of Insects. Academic Press. pp. 1094-1096
2. ^ ^{a b c} Borror, D.J., Triplehorn, C.A. Johnson. ( 1989) Introduction to the Study of Insects. 6th ed. Brooks Cole.
3. ^ Kathirithamby, Jeyaraney. 2002. Strepsiptera. Twisted-wing parasites. Version 24 September 2002. [1] in The Tree of Life Web Project
4. ^ Piper, Ross (2007), Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, Greenwood Press.
5. ^ Kathirithamby, Jeyaraney (2001) Stand Tall and They Still Get You in Your Achilles Foot-Pad. Proceedings: Biological Sciences. 268(1483):2287-2289.
6. ^ 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.
7. ^ Beani, Laura (2006) Crazy wasps: when parasites manipulate the Polistes phenotype. Ann. Zool. Fennici 43:564-574 PDF
8. ^ Kathirithamby, J (2000) Morphology of the female Myrmecolacidae (Strepsiptera) including the apron, and an associated structure analogous to the peritrophic matrix. Zool. J. Linn. Soc. 128:269-287
9. ^ 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 PDF
10. ^ Wojcik, Daniel P. (1989) Behavioral Interactions between Ants and Their Parasites. The Florida Entomologist. 72(1):43-51.
11. ^ Michael F. Whiting (1998) Long-Branch Distraction and the Strepsiptera. Systematic Biology 47(1):134-138. PDF
12. ^ ^{a b} 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.
13. ^ 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.
14. ^ Huelsenbeck, John P. (1998) Systematic Bias in Phylogenetic Analysis: Is the Strepsiptera Problem Solved? Systematic Biology. 47(3):519-537.

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
• Family outline: Strepsiptera

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