CASTE FORMATION IN THE POLYEMBRYONIC WASP COPIDOSOMA-FLORIDANUM (HYMENOPTERA, ENCYRTIDAE) - IN-VIVO AND IN-VITRO ANALYSIS

The polyembryonic wasp Copidosoma floridanum produces two morphologica lly distinct types pf larvae in its host Trichoplusia ni. Reproductive larvae consume the host, pupate, and form adult wasps, whereas precoc ious larvae manipulate the sex ratios of the reproductive caste and de fend the brood against interspecific competitors, Previous study indic ated that morphogenesis of the reproductive caste was associated with a 9-day competency period, and that ecdysteroids of host origin were r equired for completion of embryogenesis. Here we investigated whether factors associated with the host environment mediate morphogenesis of precocious larvae and caste determination, Embryogenesis of precocious larvae was found to be synchronized with specific stages of the host first-fourth instars, However, development of precocious larvae did no t depend on environmental factors specifically associated with these h ost stages, Elevation of the host juvenoid titer using the analogue me thoprene induced T. ni to undergo a supernumerary sixth instar, but di d not alter the proportion of wasp embryos that developed into precoci ous and reproductive larvae, In contrast, embryos competent to initiat e morphogenesis developed into precocious Larvae when transplanted int o novel host stages such as pupae, Development of precocious larvae wa s arrested by ablation of the host's source of ecdysteroids, but could be rescued dose-dependently by injection of 20-hydroxyecdysone, In vi tro rearing studies confirmed that completion of embryogenesis of the precocious caste required an exogenous pulse of 20-hydroxyecdysone Com bined with previous studies, our results indicate that embryos forming precocious and reproductive larvae acquire the competence to undergo morphogenesis at different times, However, we find no evidence to sugg est that caste determination is mediated by environmental factors asso ciated with a specific stage of the host. (C) 1997 Elsevier Science Lt d.