HOST STAGE SELECTION AND SEX ALLOCATION BY GYRANUSOIDEA-TEBYGI (HYMENOPTERA, ENCYRTIDAE), A PARASITOID OF THE MANGO MEALYBUG, RASTROCOCCUS-INVADENS (HOMOPTERA, PSEUDOCOCCIDAE)

Host stage selection and sex allocation by Gyranusoidea tebygi Noyes ( Hym,, Encyrtidae) were studied in choice and no-choice experiments in the laboratory. The parasitoid reproduced on first, second, and third instars of the mango mealybug, Rastrococcus invadens Williams (Hem., P seudococcidae), and it avoided hosts that were already parasitized. Ho st feeding was occasionally observed. Sex ratios of the offspring prod uced by individual wasps were highly biased in favor of females, where as the sex ratio of groups of wasps foraging under crowded conditions varied from male biased in smaller hosts to female biased in larger ho sts. Females had longer developmental times than males, developed fast er in larger mealybugs than in smaller ones, and were always larger th an males emerging from the same host instar. Their size increased with the instar of the host at oviposition. About 90% of all ovipositions in second and third instar nymphs resulted from an attack with multipl e stings, starting with a sting in the head of the host for the most p art. The function of these head stings is either to assess quality of the host or to subdue hosts prior to oviposition. Encounter rates, num ber of attacks, and number of stings during one attack increased, whil e ovipositions decreased with host instar. Time investment per oviposi tion and time spent preening increased with increasing host age becaus e older hosts defended themselves more vigorously than younger ones. T hus, while fitness of the parasitoid increased with host size, fitness returns per time decreased. The implications of this host selection b ehavior for the biological control of the mango mealybug are discussed . (C) 1995 Academic Press, Inc.