RESISTANCE TO PROTECTANT INSECTICIDES IN 2 FIELD STRAINS OF THE STORED-PRODUCT INSECT PARASITOID BRACON-HEBETOR (HYMENOPTERA, BRACONIDAE)

Field strains of the parasitoid Bracon (Habrobracon) hebetor Sav (Hymenoptera: Braconidae) collected in corn and peanut storage facilities in Blackville, SC, and Hawkinsville, GA, were 7.6- and 7.3-fold more resistant to malathion, respectively, than was a laboratory strain with which they were compared. We detected much higher levels of malathion resistance (>270-fold that of a susceptible strain) in a pyralid host Plodia interpunctella (Hubner) collected at the same facilities. Results of serial time-response bioassys with a single pesticide dose indicated that adult males of the Blackville (SCC) strain of B. hebetor were significantly more sensitive to malathion than were females, perhaps because of their smaller (1.3-fold) size (weight). In the timed bioassay, sensitivities of laboratory and SCC strains of the parasitoid to several common grain protectants were chlorpyrifos-methyl > pirimiphosmethyl > deltamethrin > cyfluthrin > malathion. The SCC strain of B. hebector was significantly more tolerant of deltamethrin, cyfluthrin, and malathion, compared with the laboratory strain. S,S,S-tributyl phosphorotrithioate (DEF) synergized malathion against the SCC strain but was slightly toxic by itself. Triphenyl phosphate (TPP) substantially delayed the toxicity of malathion in the SCC strain. We discuss the relatively low level of resistance development in B. hebetor, compared with that of the host P. interpunctella, in terms of the behavioral af ecology of host location by the parasitoid.