Changes in Numbers in the Parasitoid Complex Associated With the Diamond-Back Moth, Plutella Xylostella (L.) (Lepidoptera), in Victoria.

Abstract

Between 1972 and 1974, a study was made of parasitoids of P. xylostella naturally infesting four successive crops of cabbages which had not received any pesticide treatment. Parasitism fluctuated in each crop, averaging 49% during the study. The major parasitoid species were Diadegma cerophaga, Thyraeella collaris and Diadegma rapi, which averaged 93% of parasitism over the study period. Six minor primary parasitoid and one hyperparasite species were also recorded. Parasitoid activity was high during spring and summer, although extremely high temperatures during summer reduced numbers of both the host and its parasitoids. Drought conditions accentuated this. Parasitism in autumn depended upon the severity of this depletion and on the ensuing rate of recovery. The more important larval parasitoids were closely synchronized with host numbers, with a distinct lag during the winter period.