The Twisted-wing Parasites AKA Stylopids

Truly the most obscure and bizarre of all the insects, twisted-wing parasites have not yet been classified to the agreement of all scientists. Placed in the order called Strepsiptera, the word translates literally to “twisted wing” and references the strange twisted shape of the wings while a male is in flight. It is only the males that bear these wings. They have two pairs, consisting of forewings greatly reduced to look and function like the halteres of flies, and sparsely veined, fan-shaped hind wings. Completing it’s bizarre appearance, males have flabellate, branched antennae, and raspberry-like eyes; the latter very unusual among living insects and forming a modern counterpart to the structural plan proposed for the eyes of trilobites! Most of the known species have only been identified from specimens of the males. Females are much harder to find and are probably often overlooked since they live as grub-like parasites inside their host insect. Devoid of eyes, antennae, legs and external genitalia (except in the family Mengenillidae), the fused head and thorax projects from the host. With a greatly reduced mouth and a single genital opening, sex pheromones are emitted to attract the free-living males. After mating, fertilized eggs are retained within the female who later gives birth to six-legged larvae. The mobile larvae will go out and seek new hosts, dropping off the host insect that bears their mother as it travels about. Once another host insect is found, the larvae burrow inside, feeding until they reach maturity. They then pupate within the still living host. Later, males will emerge to seek out the females (which means that the host may now become permanent residence for several females). Though twisted-wing parasites do not feed on their host’s vital organs, they do greatly reduce nutrient intake and can affect the size of body parts, often causing the genitalia of the host to be so reduced as to render the individual sterile. So far, it is known that they parasitize silverfish (Lepismatidae), cockroaches (Blattidae), mantids (Mantidae), crickets (Gryllidae, Gryllotalpidae, Tettigoniidae), pygmy mole-crickets (Tridactylidae), plantlice (Psyllidae), Auchenorrhynchans (Cercopidae, Cicadellidae, Membracidae, Delphacidae, Dictyopharidae, Eurybrachidae, Ricaniidae, Flatidae, Fulgoridae, Issidae, Tettigometridae), true bugs (Coreidae, Cydnidae, Lygaeidae, Pentatomidae, Scutelleridae), flies (Tephritidae, Platysomatidae) and a wide range of Hymenopterans (Formicidae, Mutillidae(?), Vespidae (Masarinae, Eumeninae, Polistinae, Vespinae), Sphecidae, Colletidae, Halictidae, Andrenidae). Once thought to be beetles, they also share traits with flies. Strepsipterans do not appear in the fossil record until the Cretaceous (136-64 million years ago). There are about 500 species known, with the greatest number occurring in the tropics.

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