The Effect of Aggregation on Egg and Larval Survival in Neodiprion swainei Midd. (Hymenoptera: Diprionidae)

Abstract

Recent laboratory studies have shown that the type of spatial distribution of a host or prey population may affect the degree of natural control exerted by parasites and predators. For example, Burnett (1958) showed that the rate of paratisitism of the greenhouse whitefly, Trialeurodes vaporarium (Westw.), by Encarsia formosa Gahan, was considerably greater when the hosts were aggregated than when regularly distributed. In this case, searching parasites were better able to find groups of hosts than isolated ones. Similar results have been obtained by Huffaker (1958) in experiments with a predatory mite, Typhlodroms occidentalis Nesbitt, and a phytophagous mite, Eotetranychus sexmaculatus (Riley). Other important effects of aggregation are evident in the growing literature on this subject, as exemplified by the work of Long (1955), Mizuta (1960), and Morimoto (1960), who showed that the rate of development of some lepidopterous larvae in groups is greater than that of isolated larvae.