Divergent Host Relationships of Males and Females in the Parasitoid Encarsia porteri (Hymenoptera: Aphelinidae)

Abstract

Heterotrophic parasitoids have been reported in the aphelinid genus Encar- sia. These are species in which females develop as primary internal parasitoids of whitefly and males develop as primary internal parasitoids of lepidopteran eggs. The obligate nature of the host relationships in these aphelinids has been questioned and was investigated in this study. We examined the oviposition of female Encarsia porteri (Mercet) in 3 host types: bollworm eggs (Helicoverpa zea (Boddie)), sweetpotato whitefly nymphs (Bemisia tabaci (Gennadius)), and early pupal wasps (E. porteri). Although males of most Encarsia species develop on wasp pupae as hyperparasitoids, female E. porteri did not generally oviposit in wasp pupae. Whitefly nymphs were parasitized almost exclusively by mated females, whereas both mated and un- mated females oviposited in moth eggs. The suitability of the above hosts as well as pupal E. fonnosa were also investigated for the development of male progeny. Males were produced only on moth eggs. Thus, we conclude that the heterotrophic host relationships of E. porteri are indeed obligate. Larval E. porteri are sexually dimorphic. Early instars of male larvae have a sculptured cuticle, bear long spines along the venter, and have horn-like projections on the head capsule. Females, in contrast, are more typically hymenopteriform with weak scleroti- zation of the head capsule, indistinct segmentation, and a smooth cuticle. Also, although both male and female early instar larvae are enclosed within a membrane, only females are envel- oped by an opaque cellular layer within this membrane. WHEN 2 OR more disparate kinds of food or hab- itat are required to maintain a population, the re- sources are generally used in sequence by mor- phologically specialized life stages. Less commonly, male and female immature stages may be special- ized on different resources; these systems have been called by Walter (1983a). In heteronomous species, male and female larval morphology and behavior may be very different and may evolve more or less independently (Slat- kin 1984). Like systems in which morphological specialization occurs within the same sex but in different generations, the evolution of sexual di- morphism in heteronomous species is not subject to the same sorts of developmental constraints as in species with sequential specialization. Multige- nerational and heteronomous morphological spe- cialization is constrained only by the different forms having genes in common (Moran 1994).