Editing Strepsiptera (section)

==Biology==

=== Appearance and structure ===

==== Males ====
Males of the Strepsiptera have [[insect wing|wings]], [[arthropod leg|legs]], [[compound eye|eye]]s, and [[antenna (biology)|antennae]], though their [[Arthropod mouthparts|mouthparts]] cannot be used for feeding. Many have mouthparts modified into sensory structures. The males bear a superficial resemblance to flies.<ref name="insencyc" /> The forewings are modified into small club-shaped structures called [[halteres]], which sense [[gyroscopic]] information.<ref>{{Cite journal |last1=Pix |first1=W. |last2=Nalbach |first2=G. |last3=Zeil |first3=J. |date=August 1993 |title=Strepsipteran forewings are haltere-like organs of equilibrium |url=http://link.springer.com/10.1007/BF01138795 |journal=Naturwissenschaften |language=en |volume=80 |issue=8 |pages=371–374 |doi=10.1007/BF01138795 |bibcode=1993NW.....80..371P |s2cid=43790345 |issn=0028-1042}}</ref> A similar organ exists in flies, though in that group the hindwings are modified instead, and the two groups are thought to have independently evolved the structures.<ref>{{Cite journal |last1=Rokas |first1=Antonis |last2=Holland |first2=Peter W.H. |date=November 2000 |title=Rare genomic changes as a tool for phylogenetics |url=https://linkinghub.elsevier.com/retrieve/pii/S0169534700019674 |journal=Trends in Ecology & Evolution |language=en |volume=15 |issue=11 |pages=454–459 |doi=10.1016/S0169-5347(00)01967-4|pmid=11050348 }}</ref> The hindwings are generally fan-shaped, and have strongly reduced [[Insect wing#Venation|venation]]. The antennae are [[Insect morphology#Antennae|flabellate]], and are covered in specialised [[chemoreceptor]]s, likely to detect females over long distances.<ref name=":4">{{Cite journal |last1=Pohl |first1=Hans |last2=Beutel |first2=Rolf Georg |date=July 2008 |title=The evolution of Strepsiptera (Hexapoda) |url=https://linkinghub.elsevier.com/retrieve/pii/S0944200608000135 |journal=Zoology |language=en |volume=111 |issue=4 |pages=318–338 |doi=10.1016/j.zool.2007.06.008|pmid=18356032 |bibcode=2008Zool..111..318P }}</ref>

Adult male Strepsiptera have eyes unlike those of any other [[insect]], resembling the eyes found in the [[trilobite]] group [[Phacopina]]. Instead of a [[compound eye]] consisting of hundreds to thousands of [[ommatidia]], that each produce a [[pixel]] of the entire image, the strepsipteran eyes consist of only a few dozen "eyelets"  that each produce a complete image. These eyelets are separated by cuticle and/or setae, giving the cluster eye as a whole a blackberry-like appearance.<ref name="insencyc" /><ref>{{cite journal |author1=Buschbeck, E. K. |author2=B. Ehmer |author3=R. R. Hoy |year=2003 |title=The unusual visual system of the Strepsiptera: external eye and neuropils |url=http://hoylab.cornell.edu/hoy/buschbeck_ehmer_hoy2003.pdf |journal=Journal of Comparative Physiology A |volume=189 |issue=8 |pages=617–630 |doi=10.1007/s00359-003-0443-x |pmid=12879355 |s2cid=21888897}}</ref>

==== Females ====
The females of Stylopidia, which includes 97% of all described strepsipteran species and all modern strepsipteran families except [[Mengenillidae]] and [[Bahiaxenidae]], are not known to leave their hosts and are [[neotenic]] in form, lacking wings, legs, and eyes, but have a well [[sclerotised]] [[cephalothorax]] (fused head and [[Thorax (arthropod anatomy)|thorax]]).<ref name="insencyc" /><ref name=":3">{{Cite journal |last1=Pohl |first1=Hans |last2=Gorb |first2=Elena V. |last3=Gorb |first3=Stanislav N. |date=2020-01-01 |title=Traction force measurements on male Strepsiptera (Insecta) revealed higher forces on smooth than on hairy substrates |journal=Journal of Experimental Biology |volume=223 |issue=Pt 18 |language=en |pages=jeb.223784 |doi=10.1242/jeb.223784 |pmid=32719048 |issn=1477-9145|doi-access=free }}</ref><ref name=":4" /> Adult female mengenillids are wingless but are free living and somewhat mobile with legs and small eyes. This is probably also true for the bahiaxenids, though this has not been observed.<ref>{{Cite journal |last1=Tröger |first1=Daniel |last2=Beutel |first2=Rolf G. |last3=Pohl |first3=Hans |date=May 2019 |title=The abdomen of a free-living female of Strepsiptera and the evolution of the birth organs |url=https://onlinelibrary.wiley.com/doi/10.1002/jmor.20981 |journal=Journal of Morphology |language=en |volume=280 |issue=5 |pages=739–755 |doi=10.1002/jmor.20981 |pmid=30892750 |s2cid=84185553 |issn=0362-2525}}</ref><ref name=":3" /><ref name=":4" />

==== Larvae ====
Newly hatched primary (first [[instar]]) larvae are on average {{Convert|230|μm|in|frac=128}} in length, smaller than many single-celled organisms. They are highly mobile with well developed [[stemmata]], which are able to distinguish color. The underside of the body is covered in minute hair-like structures (microtrichia), which allow the larvae to stick to wet surfaces via [[capillary action]]. At the back of the body are well developed large bristle-like [[Cercus|cerci]], which are attached to muscles, which allow the larvae to jump. The [[Arthropod leg#Tarsus|tarsal]] segment of their legs have structures which allow them to cling to their hosts. Later larval instars which develop inside the host are completely immobile.<ref name=":4" />

{{gallery|Mengenilla moldrzyki female.jpg|Free living female of ''[[Mengenilla moldrzyki]]'' ([[Mengenillidae]])|Xenos yangi.jpg|Male pupa head (top left) and adult female of ''[[Xenos (insect)|Xenos]] yangi'' (Stylopidia, [[Xenidae]]) in ventral view (right) and closeup of the [[cephalothorax]] (centre and bottom left)|Andrena nivalis, stylopid, U, Cocos Co., NH, back 2015-07-13-15.57.01 ZS PMax (cropped2).jpg|Recently hatched larvae of a stylopid strepsipteran on the bee ''[[Andrena nivalis]]''|Xenos peckii head closeup.png|Closeup of the head of male ''[[Xenos peckii]]''|File:Stylops melittae f1.jpg|''[[Stylops melittae]]'' ([[Stylopidae]]) female stylopizing bee ''[[Andrena vaga]]'', exposing its cephalothorax|Strepsiptera.png|Adult male strepsipteran in dorsal view, halteres highlighted with red arrows|||width=200|height=200}}

=== Life cycle ===
[[File:Traumatic-insemination-and-female-counter-adaptation-in-Strepsiptera-(Insecta)-srep25052-s2.ogv|left|thumb|[[Traumatic insemination]] of an [[endoparasitic]] female in ''[[Stylops|Stylops ovinae]]'']]Virgin females release a [[pheromone]] which the males use to locate them.<ref name="insencyc" /> Mating in at least some species is [[Polyandry in nature|polyandrous]], where the female mates with more than one male.<ref name=":1">{{Cite journal |last1=Peinert |first1=Miriam |last2=Wipfler |first2=Benjamin |last3=Jetschke |first3=Gottfried |last4=Kleinteich |first4=Thomas |last5=Gorb |first5=Stanislav N. |last6=Beutel |first6=Rolf G. |last7=Pohl |first7=Hans |date=2016-04-29 |title=Traumatic insemination and female counter-adaptation in Strepsiptera (Insecta) |journal=Scientific Reports |volume=6 |pages=25052 |doi=10.1038/srep25052 |issn=2045-2322 |pmc=4850473 |pmid=27125507|bibcode=2016NatSR...625052P }}</ref>

In the Stylopidia, the female's anterior region protrudes out between the segments of the host's abdomen. In all strepsipterans the male mates by rupturing the female's [[Arthropod cuticle|cuticle]] (in the case of Stylopidia, this is in a deep narrow fissure of the cephalothorax near the birth canal). Sperm passes through the opening directly into the body in a process called [[traumatic insemination]], which has independently evolved in some other insects like [[bed bug]]s.<ref name="insencyc" /><ref name=":1" />

Strepsiptera eggs hatch inside the female, and the [[planidium|planidium larvae]] can move around freely within the female's [[haemocoel]]; this behavior is unique to these insects.<ref name=":2">[[Ross Piper|Piper, Ross]] (2007), ''Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals'', [[Greenwood Press]].</ref> The offspring consume their mother from the inside in a process known as haemocoelous [[viviparity]]. Each female produces many thousands of planidium larvae.<ref name="borror" /> The larvae emerge from the brood opening/canal on the female's head, which protrudes outside the host body.<ref name=":2" /><ref name="borror">{{cite book|author1 = Borror, D.J.|author2 = Triplehorn, C.A.|author3 = Johnson, N.F.| year=1989 |title= Introduction to the Study of Insects|edition=6|publisher=Brooks Cole}}</ref>

Larvae have legs and actively seek out new hosts. Their legs are partly vestigial in that they lack a [[Arthropod leg#Trochanter|trochanter]], the leg segment that forms the articulation between the basal [[Arthropod coxa|coxa]] and the [[Arthropod leg#Femur|femur]].<ref name="borror" /> The larvae are very active as they only have a limited amount of time to find a host before they exhaust their energy reserves. These first-[[instar]] larvae have [[stemmata]] (simple, single-lens eyes). When the larvae 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.{{citation needed|date=October 2018}} Larvae of ''Stichotrema dallatorreanum'' Hofeneder from [[Papua New Guinea]] were found to enter their [[orthoptera]]n host's tarsus (foot).<ref>{{cite journal | last1 = Kathirithamby | first1 = Jeyaraney | year = 2001 | title = Stand tall and they still get you in your Achilles foot-pad | journal = Proceedings of the Royal Society of London B: Biological Sciences | volume = 268 | issue = 1483| pages = 2287–2289 | doi=10.1098/rspb.2001.1810| pmc = 1088878 | pmid=11703867}}</ref>

Once inside the host, they undergo [[hypermetamorphosis]] and transform into 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 the older cuticle separates but is not discarded ("[[apolysis]] without [[ecdysis]]"), so multiple layers form around the larvae.<ref>{{cite journal | last1 = Kathirithamby | first1 = Jeyaraney | last2 = Ross | first2 = Larry D. | last3 = Johnston | first3 = J. Spencer | year = 2003 | title = Masquerading as Self? Endoparasitic Strepsiptera (Insecta) Enclose Themselves in Host-Derived Epidermal Bag | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 100 | issue = 13| pages = 7655–7659 | doi=10.1073/pnas.1131999100 | pmid=12788973 | pmc=164643| bibcode = 2003PNAS..100.7655K | doi-access = free }}</ref> Male larvae pupate after the last moult, but females directly become neotenous adults.<ref>{{cite journal|author=Beani, Laura |year=2006|title= Crazy wasps: when parasites manipulate the ''Polistes'' phenotype| journal= Annales Zoologici Fennici |volume=43| pages=564–574 |url=http://www.sekj.org/PDF/anz43-free/anz43-564.pdf}}</ref><ref>{{cite journal|author = Kathirithamby, J |year=2000| title= Morphology of the female Myrmecolacidae (Strepsiptera) including the ''apron'', and an associated structure analogous to the peritrophic matrix| journal= Zoological Journal of the Linnean Society|volume= 128|issue=3| pages=269–287| doi=10.1111/j.1096-3642.2000.tb00164.x|s2cid=83484969 |doi-access=free}}</ref> The colour and shape of the host's abdomen may be changed and the host usually becomes sterile. The parasites then undergo [[pupation]] to become adults. Adult males emerge from the host bodies, while females stay inside. Females may occupy up to 90% of the abdominal volume of their hosts.<ref name="insencyc" /> Adult males are very short-lived, usually surviving less than five hours, and do not feed.<ref name="insencyc" />

=== Parasitism ===
Strepsiptera of various species have been documented to attack hosts in many orders, including members of the orders [[Zygentoma]] (silverfish and allies), [[Orthoptera]] (grasshoppers, crickets), [[Blattodea]] (cockroaches), [[Mantodea]] (praying mantis), [[Heteroptera]] (bugs), [[Hymenoptera]] (wasps, ants and bees), and [[Diptera]] (flies). In the strepsipteran family [[Myrmecolacidae]], the males parasitize ants, whereas the females parasitize Orthoptera.<ref name="insencyc" /> Members of [[Mengenillidae]] target Zygentoma exclusively,<ref name=":5">{{Cite journal |last1=Engel |first1=Michael S. |last2=Huang |first2=Diying |last3=Breitkreuz |first3=Laura C.V. |last4=Azar |first4=Dany |last5=Cai |first5=Chenyang |last6=Alvarado |first6=Mabel |date=March 2016 |title=A new twisted-wing parasitoid from mid-Cretaceous amber of Myanmar (Strepsiptera) |journal=Cretaceous Research |language=en |volume=58 |pages=160–167 |doi=10.1016/j.cretres.2015.10.008|doi-access=free |bibcode=2016CrRes..58..160E }}</ref> whereas Stylopidia targets only [[winged insects]], with a large number of stylopidians targeting wasps and bees, whereas the largest family of strepsipterans, the [[Stylopidae]], with over 27% of all described strepsipterans, targets bees exclusively.<ref name=":4" />

Very rarely, multiple females may live within a single stylopized host; multiple males within a single host are somewhat more common.<ref name="insencyc" />

Strepsiptera of the family Myrmecolacidae can [[Behavior-altering parasite|influence their host's behaviour]], causing their ant hosts to linger on the tips of grass leaves, increasing the chance of being found by strepsipteran males (in the case of females) and putting them in a good position for male emergence (in the case of males).<ref>{{Cite journal| doi = 10.2307/3494966| issn = 0015-4040| volume = 72| issue = 1| pages = 43–51| last = Wojcik| first = Daniel P.| title = Behavioral Interactions between Ants and Their Parasites| journal = The Florida Entomologist| date = 1989| jstor = 3494966| url = https://naldc-legacy.nal.usda.gov/naldc/download.xhtml?id=23159&content=PDF}}</ref>