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 (Hyme noptera: Braconidae) collected in corn and peanut storage facilities i n Blackville, SC, and Hawkinsville, GA, were 7.6- and 7.3-fold more re sistant 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. Resul ts of serial time-response bioassys with a single pesticide dose indic ated that adult males of the Blackville (SCC) strain of B. hebetor wer e significantly more sensitive to malathion than were females, perhaps because of their smaller (1.3-fold) size (weight). In the timed bioas say, sensitivities of laboratory and SCC strains of the parasitoid to several common grain protectants were chlorpyrifos-methyl > pirimiphos methyl > deltamethrin > cyfluthrin > malathion. The SCC strain of B. h ebector was significantly more tolerant of deltamethrin, cyfluthrin, a nd malathion, compared with the laboratory strain. S,S,S-tributyl phos phorotrithioate (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 re latively low level of resistance development in B. hebetor, compared w ith that of the host P. interpunctella, in terms of the behavioral af ecology of host location by the parasitoid.