SEQUENTIAL ALLOCATION OF OFFSPRING SEXES IN THE HYPERPARASITOID WASP,DENDROCERUS-CARPENTERI

Mated females of Dendrocerus carpenteri produce 'precise' sex ratios, with less than binomial variance, by adjusting the sequence of male an d female eggs laid during a single oviposition bout. This wasp is a so litary hyperparasitoid of the prepupal and pupal stages of aphidiid pa rasitoids inside mummified aphids. The influence of order and quality (indexed by mummy size) of sequentially encountered hosts on offspring sex allocation was examined. Females typically laid a fertilized egg (=daughter) if the first host encountered was of high quality, but lai d an unfertilized egg (=son) if the host was of low quality. The sex o f the second egg generally was opposite that of the first, regardless of host quality. Host quality influenced the sex ratio response to the third and later hosts accepted during a single oviposition bout, howe ver, with females fertilizing a greater proportion of eggs if quality was high. With each additional egg laid, the brood sex ratio asymptoti cally approached an equilibrium value that apparently depended on the average host quality per patch. The production schedule of sons and da ughters was reset to zero after a period during which no hosts were en countered. Wasps may use simple decision rules to ensure that daughter s will find mates, regardless of variations in host quality and patch size. (C) 1996 The Association for the Study of Animal Behaviour