Response of adult parasitoids of Bemisia tabaci (Hom: Aleyrodidae) to leaf residues of selected cotton insecticides

The contact toxicity of eight insecticides to adults of four parasitoids of the sweetpotato whitefly Bemisia tabaci was evaluated in the laboratory. Two common Texas species, Eretmocerus sp. and Encarsia pergandiella Howard, and two exotic species, Eretmocerus mundus Mercet from Spain and Encarsia formosa Gahan from Greece were tested. Insecticides, applied as sprays to greenhouse-grown cotton plants at recommended rates were amitraz (Ovasyn(R)), azinphosmethyl (Guthion(R)), bifenthrin (Capture(R)), buprofezin (Applaud(R)), cypermethrin (Ammo(R)), methyl parathion and thiodicarb (Larvin(R)), with a water control. Parasitoid adults were confined on discs cut from leaves (1) sprayed the same day and (2) sprayed two days previously. Survival in both treatments was measured two and four days following exposure. Significant differences in toxicity were detected among the insecticides. Buprofezin was not toxic to any of the four parasitoids. When caged on leaves sprayed two days previously, only amitraz of the remaining compounds allowed significant general parasitoid survival after two days. E. mundus exhibited the greatest overall tolerance to insecticides, with 40 % or more surviving 48 hr after confinement on leaves sprayed with amitraz, thiodicarb and cypermethrin. Survival was generally much reduced after 96 hr. In a separate test, fresh residues of endosulfan (Thiodan(R)) were highly toxic at the two rates tested, but two day old residues at the lower rate allowed 76.7 % survival of E. mundus and 35 % survival of E. pergandiella after 48 hrs.