The functional response of Uscana lariophaga under different egg distributions of its host Callosobruchus maculatus

The functional response of the egg parasitoid Uscana lariophaga Steffan (Hymenoptera: Trichogrammatidae) was tested under three different host distributions (even, clumped and random) within clusters of Callosobruchus maculatus Fab. (Coleoptera: Bruchidae) eggs. A Holling Type II functional response was found for all three distributions. Over low host densities, less than 50% of the host clusters was parasitized. At low host densities, U. lariophaga females parasitized significantly fewer eggs in random egg clusters with many beans than in clusters with fewer beans and an even or clumped egg distribution. At higher egg densities, plateau levels of maximum number of hosts parasitized were the same for all three egg distributions. Uscana lariophaga appears to be adapted to search for even or clustered egg distributions, as can be found in the field and under storage conditions.