Introduction to Twisted Wing Parasites Order Strepsiptera

Parasites are often hard to identify because they are so adapted to their parasitic way of life.  Strepsiptera are no exception.  They are insects to be sure but exactly who they are related to is more difficult to ascertain.  Most people have never seen a strepsipteran because of their parasitic life style.  Their name means twisted wing and they live in the bodies of other insects.  About 600 species have been identified and all are parasitic.  Some similarities to beetles, such as using their hind wings for flight, indicates that the Coleoptera may be a sister group. Other scientists have championed a relationship with the Diptera (true flies) on the basis of body structure and similar DNA sequences, but the question is by no means answered yet and will require further studies.

Strepsiptera are relatively host specific, with species of each family found only in one insect order, although within that order a strepsipteran species may infect several different host species.  The family Elenchidae for instance are found only in grasshoppers.  Strepsiptera have been identified from cockroaches, mantids, thrips, bugs and flies but most are parasitic on Hymenoptera, especially wasps and bees.

The Strepsiptera demonstrate extreme sexual dimorphism due to differences in life styles of the sexes.  The males look like proper insects, with six legs, buggy eyes and fan-shaped antennae.  They spend some time living free, using their twisted little wings to look for females.  Since they do not feed as adults, their mouthparts are reduced in size and non-functional.  

Most females are larval in appearance and never develop wings or legs because they spend their lives in their hosts, with only their fused cephalothoraxes exposed between the host’s ventral abdominal plates.  The females release pheromones so they can be found and fertilised by a passing male through a brood passage in the head. 

The larvae develop first in the abdomen of their mother.  They make their way out through her genital opening and then go looking for a new host.  They have six long, thin legs and are able to walk and jump.   When they find a suitable host, they burrow in through the cuticle and then mature.  The males emerge but the female remains in her puparium for life.  They are relatively harmless parasites and do not kill their hosts, although they may be uncomfortable.

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