Competition between Anisopteromalus calandrae and Choetospila elegans (Hymenoptera: Pteromalidae) at Different Parasitoid Densities on Immature Rice Weevils (Coleoptera: Curculionidae) in Wheat

Competition between parasitoids was studied by exposing immature rice weevils, Sitophilus oryzae (L.), developing in wheat to Anisopteromalus calandrae (Howard) alone, Choetospila elegans Westwood alone, or both species together. With A. calandrae only, the emergence of A. calandrae progeny tended to peak near four or eight female parasitoids and parasitoid-induced mortality increased with increasing parasitoid numbers. With C. elegans only, parasitoid emergence increased, but parasitoid-induced mortality did not change with an increase in numbers of parasitoids. A. calandrae in combination with C. elegans produced similar reductions in rice weevil populations, as did A. calandrae alone. C. elegans alone was less efficient than A. calandrae alone at low parasitoid densities, but when numbers of C. elegans reached higher densities, rice weevil mortality was as great as that with A. calandrae alone. Under competitive conditions, the sex ratio (female percentage) of C. elegans was decreased by the presence of A. calandrae, but the sex ratio of A. calandrae was not affected by C. elegans. Competition reduced emergence of both A. calandrae and C. elegans; however, A. calandrae was clearly the dominant species when rice weevils were exposed to equal numbers of both species of parasitoids.