Evaluation of Field Introductions of Two Insect Parasites (Hymenoptera: Braconidae) for Controlling Potato-infesting Aphids

Abstract

Two hymenopteran parasites, Diaretiella rapae (M'Intosh) and an as yet undescribed species of Praon that were reared in an insectary on green peach aphids, Myzus persicae (Sulzer), infesting Chinese cabbage, were mass released as late-stage pupae (in mummified aphids) among growing, aphid-infested potato plants. From the number of parasitized aphids (from which parasites had not yet emerged) found subsequently on potato plants sampled weekly after the introductions, neither species of parasite exerted a measurable influence on aphid populations in large field cages, in small field plots, or in small fields. Both species of wasps have been reared from naturally parasitized potato-infesting aphids in northeastern Maine, both in the field and in the insectary, over a period of many years. In this experiment, the insectary-reared parasites apparently emerged satisfactorily as adults from introduced, parasitized aphids, but they did not search out and oviposit in aphids on nearby potato plants. In planning future experiments of this nature, it seems evident that much more information will be needed on the behavior of the adult parasites and their reaction to various meteorological factors in the field.