Caste Determination in the Polyembryonic Wasp Copidosoma Floridanum

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*** Polyphenism refers to the occurrence of alternative phenotypes in a species in response to cues from its internal or external environment. Most studies on insect polyphenisms have focused on how environmental and endocrine factors affect phenotypic plasticity. Implicit in this view is that individuals are initially bipotential but at a critical period, specific stimuli irreversibly commit them to a particular caste. Environment factors that influence insect polyphenisms have been examined many times previously, but how these factors impact morphogenetic events at the cell or molecular level is largely unknown. A useful system for studying these questions is a unique group of parasitic wasps (parasitoids) that are polyembryonic. Parasitoids lay their eggs on or in the bodies of other insects, which act as food for the develop larvae. Each egg laid by a polyembryonic wasp divides clonally to produce a brood of genetically identical siblings that feed together inside the host. The eggs of some species form more than 1,000 embryos and two morphologically distinct laral castes: reproductive larvae that develop into adult wasps and precocious larvae that have worker functions. In this proposal, we seek funds to study caste formation in Copidosoma floridanum, a polyembryonic wasp that attacks the moth Trichopulsiani. Our background data will allow us to characterize how cell lineage and endocrine factors interact with genes regulating pattern formation. Objectives of the proposal are to: 1) assess the role of cell lineage in caste determination, 2) examine the influence of host endocrine factors on caste, and 3) characterize spatial/temporal expression of pattern-forming genes in the precocious and reproductive morphs. For lineage studies, fate maps will be generated by injecting selected blastomeres using fluorescently conjugated dextran tracers and/or horseradish peroxidase. Endocrine studies will employ a series of transplantation, ablation and rescue strategies, while pattern formation will be examined by monitoring expression of pattern gene homologs. Our study will contribute fundamental information to our understanding of polyembyrony, the cellular/molecular mechanisms regulating alternative polyphenisms, and the processes influencing developmental evolution. ***