POPULATION-GENETICS OF AN OPPORTUNISTIC PARASITOID IN AN AGRICULTURALLANDSCAPE

Parasitoid insects that use different hosts can have a subdivided popu lation structure that corresponds to host use. A subdivided population structure may favour local adaptation of subpopulations to small-scal e environmental differences and may promote their genetic divergence. In this paper, heritable Random Amplified Polymorphic DNA (RAPD) marke rs visualized by single strand conformational polymorphisms (SSCP) ana lysis were used to examine the population structure of the parasitoid wasp Diaeretiella rapae (Hymenoptera: Braconidae) in an environment wh ere two aphid hosts are available for oviposition. We found 11 codomin ant and 34 dominant RAPD polymorphisms that conformed to Mendelian seg regation patterns. A nested analysis of variance indicated extensive g enetic differentiation among six populations of D. rapne that were sam pled for two years. Effective migration rates (Nm) between populations ranged from 1.2-1.6 per year, indicating a relatively low dispersal r ate. Genetic distances were also calculated between populations and th e resulting trees indicated that populations less than 1.0 km from eac h other were genetically differentiated. Our results indicate that D. rapae populations are genetically subdivided on a small spatial scale that corresponds to host-use patterns.