Parasitoid - Parasitoidal Insects

Parasitoidal Insects

About 10% of described insect species are entomophagous parasitoids. There are four insect orders that are particularly renowned for this type of life history. By far the majority are in the order Hymenoptera.

The largest and best-known group comprises the so-called "Parasitica" within the Hymenopteran suborder Apocrita: the largest subgroups of these are the chalcidoid wasps (superfamily Chalcidoidea) and the ichneumon wasps (superfamily Ichneumonoidea), followed by the Proctotrupoidea and Platygastroidea. Outside of the Parasitica, many other Hymenopteran lineages that include parasitoids, such as most of the Chrysidoidea and Vespoidea, and the rare Symphytan family Orussidae.

The flies (order Diptera) include several families of parasitoids, the largest of which is the family Tachinidae, and also smaller families such as Pipunculidae, Conopidae, and others. Other families of flies that are not primarily parasitoids or parasites, or at least not primarily protelean, do nonetheless include protelean species. For example Phoridae have already been mentioned as parasitoidal on ants, and at least some flesh fly species, such as Emblemasoma auditrix, are parasitoidal on cicadas, and have raised great interest because they locate their hosts by sound. The kleptoparasitic flesh fly genus Craticulina has already been mentioned and logically qualifies as a protelean fly genus.

Two other orders with parasitoidal members are the "twisted-wing parasites" (order Strepsiptera), which is a small group consisting entirely of parasitoids, and the beetles (order Coleoptera), which includes at least two families, Ripiphoridae and Rhipiceridae, that are largely parasitoids, and rove beetles (family Staphylinidae) of the genus Aleochara. Occasional members of other orders can be parasitoids; one of the more remarkable is the moth family Epipyropidae, which are ectoparasitoids of planthoppers and Cicadas. The genus Cyclotorna has even more elaborate habits, beginning its growth period parasitising plant bugs, and concluding by feeding on ant larvae in their colonies.

Hymenopteran parasitoids often have unique life cycles. In one family, the Trigonalidae, the female wasps deposit eggs into small pockets they cut into the edge of leaves with their ovipositor. A caterpillar chewing these leaves may unknowingly swallow some of the eggs, and when they get into the caterpillar's gut, they hatch and burrow through the gut wall and into the body cavity. Later they search the caterpillar's body cavity for other parasitoid larvae, and it is these they attack and feed on. Some trigonalids, once in a caterpillar or sawfly larva, need their vehicle to fall prey to a social wasp. The wasp carries the caterpillar back to its nest, and there it is butchered and fed to the wasp's young; they will serve as the host for the trigonalid, the eggs of which are in the butchered caterpillar.