Field Studies on the Effect of Pesticides on the Diamondback Moth (Lepidoptera: Plutellidae) and Parasitism by Diadegma insulare (Hymenoptera: Ichneumonidae)

Abstract

The effects of pesticides on the diamondback moth, Plutella xylostella (L.), and parasitism by Diadegma insulaTe (Cresson) was studied at the Michigan State University Entomology Research Farm during July and August 1990. The range of diamondback moth parasitism from three different locations in Michigan was 60.8–83.3%. Pesticides used were Bacillus thuringiensis var. Kurstaki (Berliner), thiodicarb, thiodicarb + B. thuringiensis , chlorpyrifos, permethrin, ICIA 0321 (pyrethroid), and esfenvalerate. Diamondback larval moth mortality was not Significantly different among the treated plots but was significantly higher than in untreated plots 3 d after spraying. The change in number of diamondback moth larvae (0 versus 3 d), and diamondback moth and D. insulare pupae (0 versus 6 d) was similar in all treatments. Parasitism by D. insulare in treated plots was not affected 6 d after spraying with any pesticide tested. Mean percentage parasitism by D. insulare in guard rows was also not different. However, the percentage parasitism in cages 3 d after treatment with permethrin, azinphosmethyl, or B. thuringiensis or untreated was 7.8, 13.3, 81.5, and 79.4%, respectively. Parasitism by D. insulare of the diamondback moth larvae seems to be influenced by the vegetation or refuge plants present outside the experimental plots. Diamondback moth parasitism by D. insulare may not be affected severely if pesticides are judiciously used.