SEX-RATIO REGULATION IN THE WASP EUPELMUS-VUILLETI (CRWF), AN ECTOPARASITOID ON BEAN WEEVIL LARVAE (HYMENOPTERA, PTEROMALIDAE)

In Africa, the seeds and/or pods of Vigna unguiculata and Vigna radiat a (Papilionacea) are attacked in fields and storage structures by bruc hid beetles Callosobruchus maculatus and Bruchidius atrolineatus, on w hich parasitoid communities can develop. One of these parasitoids is t he solitary ectoparasitoid Eupelmus vuilleti (Eupelmidae). The storage conditions of V. unguiculata and V. radiata favor the overlapping of all host stages during several months, These conditions suggest that f emale parasitoids would vary the sex ratio of their offspring accordin g to the different sizes or developmental stages of hosts. The sex rat io of E. vuilleti was strongly related to the developmental stage of t he host C. maculatus, Under our experimental conditions, where superpa rasitism is rare, the proportion of daughters varied between 5 and 25% on the third larval stage but reached 70 to 90% on the pupae, The inc rease in the proportion of daughters was also observed in the absence of superparasitism. In this case, there was an absolute coincidence be tween the sex ratio of eggs laid and that of emerged adults, Manipulat ion of the sex of the egg by the females seems to take place at the ti me of the egg's fertilization, The relation between host weight and eg g sex showed that the male eggs are preferentially laid on lighter hos t larvae and the female eggs on heavier ones.