FIELD STUDIES ON THE EFFECT OF PESTICIDES ON THE DIAMONDBACK MOTH (LEPIDOPTERA, PLUTELLIDAE) AND PARASITISM BY DIADEGMA-INSULARE (HYMENOPTERA, ICHNEUMONIDAE)

The effects of pesticides on the diamondback moth, Plutella xylostella (L.), and parasitism by Diadegma insulare (Cresson) was studied at th e Michigan State University Entomology Research Farm during July and A ugust 1990. The range of diamondback moth parasitism from three differ ent locations in Michigan was 60.8-83.3%. Pesticides used were Bacillu s thuringiensis var. Kurstaki (Berliner), thiodicarb, thiodicarb + B. thuringiensis, chlorpyrifos, permethrin, ICIA 0321 (pyrethroid), and e sfenvalerate. 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 diamondba ck moth larvae (0 versus 3 d), and diamondback moth and D. insulare pu pae (0 versus 6 d) was similar in all treatments. Parasitism by D. ins ulare in treated plots was not affected 6 d after spraying with any pe sticide tested. Mean percentage parasitism by D. insulare in guard row s was also not different. However, the percentage parasitism in cages 3 d after treatment with permethrin, azinphosmethyl, or B. thuringiens is or untreated was 7.8, 13.3, 81.5, and 79.4%, respectively. Parasiti sm by D. insulare of the diamondback moth larvae seems to be influence d 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.