Abstract
Topical application of 14 insecticides to the adult parasitoid Microplitis croceipes (Cresson) (mean weight ± SE = 5.8 ± 0.1 mg) showed that certain compounds were tolerated by the wasp. No dosage/mortality response was obtained for chlordimeform, diflubenzuron, or thiodicarb because concentrations >2,500 ng per insect were insoluble in acetone. Of the remaining 11 compounds, the organophosphate insecticide methyl parathion-EPN was most toxic (LD50 = 13.2 ng per insect), while the pyrethroid insecticide fenvalerate was least toxic (LD50 = 939.9 ng per insect). The carbamate methomyl (LD50 = 404.9 ng per insect) and the pyrethroid flucythrinate (LD50 = 397.2 ng per insect) had similar LD50’s. LD50’s(nanograms per insect) for the remaining insecticides were chlorpyrifos, 21.7; azinphosmethyl, 25.5; malathion, 52.1; sulprofos, 136.8; permethrin, 203.1; toxaphene, 246.1; and dicrotophos, 308.7. These results support the hypothesis that unusually high rates of parasitism in the field are the result of the use of pyrethroid rather than organophosphorous insecticides.
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