Twisted-Wing Parasites: Strepsiptera

The life cycles of twisted-wing parasites are complex. Adult males move about freely in the environment, while most females live their entire lives as parasites inside the bodies of other insects. However, in one group of twisted-wing parasites the females are free-living and go about their lives outside the bodies of their host insects.

Emerging adult males use an inflatable sac on their heads to burst out of their pupal case. They have only a few hours to live and spend all their time looking for a mate. Adult females are surrounded by their old larval exoskeleton inside their host. With only their head and part of their thorax sticking out of the host's body, they release pheromones (FEH-re-moans). Pheromones are chemicals that are especially attractive to males of their own species. There is no courtship. Males deposit sperm directly into the female's body by injecting it between her head and thorax. In some species the females are able to reproduce without being fertilized by a male.

The eggs remain inside the female's body and are nourished directly by the host's blood. The hatching larvae emerge from their mother and the host to search actively for a new host on nearby vegetation. Some will hitch a ride on a wasp and settle in on an egg or larva in its nest. Others simply attack the developing larvae of other insects. Once they enter the body of their new host, the larva will molt, or shed its exoskeleton, and become a legless grub. This type of development, where the larvae alternate between active, legged forms and legless grubs is called hypermetamorphosis (HAI-purh-MEH-te-MOR-fe-sihs). Hypermetamorphosis is typical of many parasitic insects. The larvae of twisted-wing parasites molt four to seven times before reaching the pupal stage. Pupation usually takes place inside the last larval exoskeleton, with just the head and thorax sticking out from between the fourth and fifth abdominal segments of the host.