EFFECTS OF EGG LOAD ON FINDING AND ACCEPTANCE OF HOST FRUIT IN CERATITIS-CAPITATA FLIES

In studies conducted on potted host trees in field cages and in the laboratory, we examined the influence of egg load on the finding and acceptance of high-ranking (kumquat) and lower-ranking (grapefruit) hosts for oviposition by wild-origin Mediterranean fruit fly females, Ceratitis capitata (Wiedemann). By prescribing the periods during which females had access to protein prior to testing, we generated four classes of females having progressively increasing egg loads but not differing in population origin, age, degree of protein hunger at testing, or amount of prior experience with host fruit (none). Egg load had no discernible effect on behaviour associated with finding either type of fruit but did have a significant effect on several behaviours associated with oviposition after alighting on fruit. Increasing egg load led to increasing propensity to engage in ovipositional-type behaviour on both kumquats and grapefruits. There was no evidence, however, to support a hypothesis that medflies would become less discriminating against grapefruits relative to kumquats as egg load increased. Relative to kumquats, grapefruits were accepted for oviposition by intermediate and high egg load females to a substantially greater degree in laboratory cages than on trees, suggesting that results of laboratory cage experiments on host discrimination by tephritid flies may poorly reflect differences in behavioural responses expressed under less constrained conditions.