HYMENOPTERA, Trigonaloidea, Trigonalidae
Description & Statistics
Trigonalidae are parasitoids of Vespidae or of parasitoids of caterpillars. Some species are primary parasitoids of the larvae of sawflies. The females deposit their eggs on foliage. In species attacking caterpillars, the eggs hatch when consumed by a caterpillar, and the trigonalid larva attacks the ichneumonid, tachinid or other parasitoid larva present within the caterpillar. In those attacking vespoid larvae, it is believed that a caterpillar, which in turn is eaten by a vespid wasp, consumes the eggs. When regurgitating the caterpillar and feeding it to its young, there is a transfer of the trigonalid larvae from the caterpillar to the wasp larva.
All members of this superfamily are small, and rather rare. There were less than 5 species kinown in North America as of 2000. Trigonalids are small and usually bright-colored and rather sturdy. They have the appearance of wasps, but their antennae are longer with at least 16 segments (Mason 1993)
This is one of the more unusual families of hymenopteran insects, of unknown affinity within the suborder Apocrita (though sometimes believed to be related to the Evanioidea), and presently placed in its own superfamily, Trigonaloidea. Trigonalidae is divided into two subfamilies, Orthogonalinae and Trigonalinae. These wasps are extremely rare but very diverse, with about 94 species in over 15 genera, and are distributed worldwide.
Studies on the biology of these insects indicates a rather unusual life history where almost all known species have females that lay thousands of minute eggs, "clamping" them to the edges or injecting them inside of leaves. The egg must then be consumed by a caterpillar. Once inside the caterpillar, the trigonalid egg either hatches and attacks any other parasitoid larvae (including its siblings) in the caterpillar, or it waits until the caterpillar has died and fed to a vespid larva, which it then attacks. Therefore, they are parasitoids or hyperparasitoids, but in a unique manner among the insects, where the eggs must be swallowed by a host. However, there are some species that are known to directly parasitize sawflies.
Townes, H. 1956. The nearctic species of trigonalid wasps. Proc. U. S. Natl. Mus. 106: 295-302.