Twisted-wing parasites / Stylopids / Strepsipterans
The name Strepsiptera, derived from the Greek "strepsi" meaning turned or twisted and "ptera" meaning wings, refers to the resting position of the male's large hind wings.
Classification & Distribution
- complete development (egg, larva, pupa, adult)
Strepsiptera exhibit hypermetamorphic development: first instars (triungulins) are free-living and highly mobile. They locate and enter the body of a host. Subsequent instars are legless, grub-like internal parasites.
Distribution: Uncommon. Larvae and adult females are internal parasites of other insects.North America
Worldwide Number of Families48 Number of Species109532
Life History & Ecology
Most Strepsiptera (also known as twisted-wing parasites) live as internal parasites of bees, wasps, grasshoppers, leafhoppers, and other members of the order Hemiptera. Only a few species that parasitize bristletails (Archeognatha) are known to be free-living in the adult stage.
Strepsiptera share so many characteristics with beetles that some entomologists classify them as a superfamily of Coleoptera. In fact, Strepsiptera and certain parasitic beetles (in the families Meloidae and Rhipiphoridae) are among the very few insects that undergo hypermetamorphosis, an unusual type of holometabolous development in which the larvae change body form as they mature. Upon emerging from their mother's body, the young larvae, called triunguloids, have six legs and crawl around in search of a suitable host. In species that parasitize bees or wasps, a triunguloid usually climbs to the top of a flower and waits for a pollinator. When a host arrives, the larva jumps aboard, burrows into its body, and quickly molts into a second stage that has no distinct head, legs, antennae or other insect-like features. These larvae grow and continue to molt inside the host's body cavity, assimilating nutrients from the blood and non-vital tissues. After pupating in the host, winged males emerge and fly in search of mates. An adult female remains inside her host, managing to attract and mate with a male while only a small portion of her body protrudes from the host's abdomen. Embryos develop within the female's body, and a new generation of triunguloid larvae begin their life cycle by escaping through a brood passage on the underside of her body.
Adult male Strepsiptera are strange-looking insects. The head is small, with protruding compound eyes that look like tiny raspberries. The antennae are multi-segmented and have up to three branches. Front wings are reduced to small, club-like structures; hind wings are very large and fan-shaped.
- First instar (triungulin) has legs, high mobility
- Successive instars are legless and grub-like with reduced mouthparts
- Females remain larviform, legless and wingless, partially projecting from host's abdomen.
- Males emerge with adult-like body
- Large fan-shaped hind wings; small club-like front wings
- Reduced mandibulate mouthparts
- Antennae 4- to 7-segmented; often with lateral branching
Strepsipterans are not abundant enough to have a significant impact on other insect populations.
There are only four families of Strepsiptera found in North America:
- Stylopidae -- most common; they parasitize wasps and bees
- Female Strepsiptera are unusually fecund. Each one may produce 2500-7000 offspring
- An insect infested with a strepsipteran parasite is often said to be "stylopized". This often results in destruction of the hosts' reproductive organs (parasitic castration), and in some cases a reversal of secondary sex characteristics (females look like males).
- Strepsipteran legs are unusual. In the first place, only first instar larvae and adult males have legs. And secondly, the trochanters, a leg segment present in all other insects, is missing in all strepsipterans.
- An oral secretion produced by triungulin larvae softens the host's exoskeleton enough to aid entry of the tiny parasite.