EVALUATION OF A RESISTANT PARASITOID FOR BIOLOGICAL-CONTROL OF WEEVILS IN INSECTICIDE-TREATED WHEAT

Interaction of a resistant strain of Anisopteromalus calandrae (Howard ) (Hymenoptera: Pteromalidae) and a host, the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), on wheat treated with malathi on was studied in the laboratory. Based oil dose response and serial t ime-response bioassays, malathion concentration had no significant eff ect on longevity fecundity, or effectiveness of the Bamberg strain of A, calandrae parasitizing S. oryzae in wheat. Suppression of the immat ure weevil population exceeded 90% on malathion-treated wheat. Bamberg A. calandrae were more successful parasitizing the Savannah laborator y strain of S, oryzae compared with the Bamberg strain of S. oryzae, p ossibly because of the larger size of the Savannah weevils. The Bamber g strain of S. oryzae (12 times resistant at the LD(99) based on vial bioassays) was more tolerant of malathion applied to wheat than was th e susceptible Savannah strain of S. oryzae, However. malathion concent ration had no significant effect on emergence of adults of either weev il strain when wheat containing immatures was treated. Although ovipos ition was significantly reduced, both weevil strains oviposited on whe at treated with malathion. These results indicate that the ecology of host development (for example, protected weevil larvae feeding within grain kernels) may be primarily responsible for development of the res istance in Bamberg A, calandrae by providing a food source when the pa rasitoid is under selection pressure. Use of the resistant strain of A . calandrae in a management system for insect pests in stored grain is discussed.