Surveys were conducted in 1981, 1983 and 1984 across the island of Puerto Rico to determine the effects of patch characteristics of the tropical herbaceous legume, Crotalaria pallida Ait. on the herbivore and its parasitoids. The mean number of flower racemes per plant and mature pods per raceme varied from year to year and appeared to be influenced by rainfall patterns, but were independent of patch size or plant density. Low larval parasitism was also observed during dry seasons. Proportion of plant patches colonized by Etiella zinckenella was smallest during dry seasons. Local extinction of C. pallida patches was found commonly, with a 77.4% extinction rate during a 6-month period. Patch extinction, which was caused mainly by human activity, was independent of patch size.

Pods of C. pallida within patches were inspected for lima bean pod borer, E. zinckenella (Lepidoptera: Phycitidae) injury. The number of pods bored per mature raceme, and the per cent of bored pods were positively correlated with the number of host-plants per patch and the (surface) area of the patch. No correlation was found between per cent parasitism and pod borer larval density. However, per cent parasitism was influenced directly by C. pallida plant density and patch surface area. Given the transient nature of C. pallida patches and the changes that occur over a season, these positive responses of parasitoids to plant density and patch surface area are important components for their successful exploitation of larval hosts.