SENSITIVITIES OF LABORATORY AND FIELD STRAINS OF THE PARASITOID ANISOPTEROMALUS-CALANDRAE (HYMENOPTERA, PTEROMALIDAE) AND ITS HOST, SITOPHILUS-ORYZAE (COLEOPTERA, CURCULIONIDAE), TO DELTAMETHRIN AND CYFLUTHRIN

Glass vial laboratory bioassays were used to evaluate sensitivities of a laboratory strain and a malathion-resistant field strain of the parasitoid Anisopteromalus calandrae (Howard) (Hymenoptera: Pteromalidae) to two pyrethroids, deltamethrin and cyfluthrin. Knockdown (24 h) and mortality (48 h) dose response data for the parasitoids were compared with those of laboratory and field strains of the parasitoid's host, the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae). For both species, higher doses were required for mortality than for knockdown. LD50s for 48 h mortality for the field strain of A. calandrae were 0.36 mug/vial for deltamethrin and 1.52 mug/vial for cyfluthrin. The malathion-resistant field strain of A. calandrae was about 2-fold more resistant to the pyrethroids compared with the laboratory strain. LD50s for the field strain of S. oryzae were 0.51 mug/vial for deltamethrin and 1.51 mug/vial for cyfluthrin. There no significant differences in response of the laboratory and field strains of S. oryzae to the pyrethroids. Although they are not currently labelled for use as grain protectants, these pyrethroids offer several advantages over organophosphorothioates in controlling stored grain insects. However, resistance ratios in A. calandrae will have to be increased, probably through laboratory selection procedures, to allow this parasitoid to be used in a pest management program in combination with these compounds.