LIMITED EVIDENCE FOR SIZE-BASED DISCRIMINATION OF OVIPOSITION SITES IN Callosobruchus maculatus (COLEOPTERA: BRUCHINAE)

Because variation in host quality and levels of intraspecific competition have been shown to affect growth, survival, and fecundity in a large number of parasitoid and obligate internally feeding granivore species, it is expected that selection will favour those females that are able to discriminate among potential hosts. Previous studies on the bruchid beetle Callosobruchus maculatus (F.) have shown that females lay more eggs on large seeds than small seeds. These studies, however, have typically presented females of a single strain with seeds that differed markedly in size. Here, we test the ability of females of two strains, which differ in their larval competition strategies, to discriminate among incremental levels of “small” versus “large” seeds. Based on previous studies, we predicted that females of both strains would exhibit a preference for larger seeds, which would increase as the difference in size increased. We also predicted that contest strain females would exhibit greater levels of discrimination than scramble strain females. Contrary to our expectations, we found low levels of discrimination for most strain × size difference combinations, and our statistically significant findings were partially due to high sample sizes and low variation in oviposition preferences. Our data on the mass and fecundity of female offspring potentially shed a light on these patterns: females from “large” seeds rarely had mean body mass or fecundity values significantly greater than those from paired “small” seeds. We advocate that future studies consider female oviposition decisions when presented with subtle variation in host quality.