Hymenopterous parasitoids associated with diamondback moth: the taxonomic dilemma

Attempts to control diamondback moth Plutella xylostella (L.) using insect parasitoids have not been entirely successful. Parasitoids which have been utilized include Diadegma species and Cotesia plutellae. A better understanding of the systematics of these Hymenoptera could lead to their more effective exploitation in biological control. Diadegma is a very large and difficult genus of lchneumonidae. There are no completely satisfactory taxonomic treatments, and from the limited work that has been done we know that some distinct biological species are almost impossible to separate using traditional, morphological characters. Nine putative species of Diadegma attack diamondback moth. So far no studies have adequately considered the taxonomic questions which are important in relation to their parasitism of this widespread pest. The microgastrine braconid Cotesia plutellae has been used with limited success in controlling diamondback moth, but recent field studies have raised suspicions that it is a complex of two or more species. We present a review of our knowledge of Diadegma and Cotesia and other microgastrines associated with diamondback moth, and attempt to outline a strategy for solving the taxonomic problems, leading to a better understanding of relationships with this host. The other parasitoids which we consider reliably recorded from diamondback moth are also noted.