EGG-LAYING BEHAVIOR IN DIVERGENT STRAINS OF THE COWPEA WEEVIL (COLEOPTERA, BRUCHIDAE) - TIME BUDGETS AND TRANSITION MATRICES

Females from two strains of the cowpea weevil, Callosobruchus maculatus (F.), differ genetically in how they distribute their eggs among host seeds. In an Indian strain, females strongly avoid adding eggs to egg-laden seeds and thus produce highly uniform egg dispersions, whereas females from a Brazilian strain produce egg dispersions that are intermediate between uniform and random. We examined whether differences in searching behavior can account for these patterns. When presented with a standard array of clean seeds, females from the two strains spent similar proportions of time engaged in eight component behaviors, although Indian-strain females tended to spend more time ''inspecting'' seeds. We found no difference between strains in the number of seeds inspected or visited between successive egg-laying bouts. Females in both strains tended to lay successive eggs on adjacent seeds in the array. Behavior sequences were constructed using a log-linear analysis of transition frequencies. Inspection of seeds appeared to play a greater role in the sequences of Indian-strain females, but most significant behavioral transitions were common to both strains. Our results suggest that differences in the allocation of eggs among resources need not reflect differences in searching behavior; in the case of C. maculatus, differential sensitivity or response to the putative marking pheromone may be primarily responsible for the divergent egg-laying patterns.