Susceptibility of Heliothis virescens (F.) (Lepidoptera: Noctuidae) Larvae To Microbial Agent-Chemical Pesticide Mixtures on Cotton Foliage 1

Abstract

Bacillus thuringiensis var. kurstaki Berliner and Heliothis nuclear polyhedrosis virus (NPV) formulations Dipel and Elcar, respectively, were tested in spray mixtures with several chemical pesticides: benomyl, chlorothalonil, fentin hydroxide, and thiabendazole (fungicides); methoprene and diflubenzuron (insect growth regulators); cyhexatin (acaricide); and chlordimeform (insecticide-acaricide) on cotton foliage. Foliage from treated plants was fed to first- and third-stage Heliothis virescens (F.) larvae. First-stage larval mortality response from microbial agent-chemical pesticide mixtures varied from synergistic to antagonistic. B. thuringiensis with either acaricide, chlordimeform or cyhexatin, and Heliothis NPV-chlordimeform produced the highest mortality above the expected levels. Mixtures of either microbial agent with chlorothalonil and diflubenzuron-B. thuringiensis resulted in significantly less mortality than the expected levels. No synergism was observed when third-stage larvae were exposed to the mixtures. B. thuringiensis-fentin hydroxide or diflubenzuron and Heliothis NPV-fentin hydroxide mixtures were antagonistic. B. thuringiensis -chlorothalonil was also antagonistic when mortality was recorded at pupation.