Egg dumping and life history strategy of Callosobruchus maculatus

Abstract.  Previous studies have demonstrated that female Callosobruchus maculatus adjust oviposition rates to cope with changes in host availability. A female lays fewer eggs when host availability is low, and hence decreases larval competition. However, females will also dump eggs on unsuitable substrates under conditions of host deprivation. Because the female does not feed as an adult, egg dumping possibly wastes energy and may thus be a maladaptive behaviour. In this study, the effect of mating and age on the egg-dumping behaviour and the life history strategy of the female are explored. Under host-deprived conditions, mating is seen to trigger egg-dumping behaviour. Also, females mated at 6 days dump significantly fewer eggs and live longer than females mated at 0 or 3 days. Thus, a trade-off between fecundity and longevity is seen among females subjected to different manipulations. In addition, 6-day-old virgin females contain more mature eggs than females mated at 6 days can produce when deprived of hosts. This finding indicates that the female reallocates internal energy resources by oosorption in a resource-limited environment. To test the maladaptive hypothesis, mated females were deprived of a host for 6 days and then given sufficient hosts each day. The results show that the more eggs dumped by a female in the first 6 days, the more eggs are laid later on beans. Egg dumping is thus not maladaptive.