Effects of sublethal dosages of certain insecticides on eggs, larvae and adults of two species of Heliothis (Lepidoptera: Noctuidae)

Abstract

Topical treatments with endrin and Guthion compounds were applied to eggs, larvae and adults of the bollworm, Heliothis zea, and the tobacco budworm, Heliothis virescens. Endrin was much more effective on larvae of both species than the Guthion compounds. Various Guthion compounds were effective on the moths of both species while endrin did not produce promising results. There was a differential susceptibility between the bollworm and the tobacco budworm on all the compounds tested. Greater dosages of all compounds were required to kill the tobacco budworm than the bollworm. The effect of insecticides on eggs were studied by observing the duration of the development period of the larvae that hatched from treated groups. At standardized dosages, larvae hatched from eggs treated with the Guthion compounds required slightly longer to complete development than those from untreated eggs. Endrin applied to eggs apparently had no effect on the development of the larval stages. Sublethal dosages were applied to third and fourth instar larvae. Endrin treated larvae showed a higher mortality after 72 hours than individuals treated with a mixture of Guthion-Ethyl-Guthion (1:1 v/v). There was a reduction in larval and pupal weight of treated individuals of both species. At standardized dosages, the fecundity of the female survivors was reduced with both species with all treatments. Greatest reductions in the average number of eggs produced per female occurred in groups treated with greatest dosages. The insecticides did not appear to have any effect on hatchability of eggs produced by surviving females.