Development of Insecticide Resistance in Heliothis zea and Heliothis virescens in North America

The bollworm, Heliothis zea (Boddie), and the tobacco budworm, H. virescens (Fabricius), have emerged as two of agriculture's most serious pests. Problems involving the control of both species are especially acute on cotton. At one time or another both species have developed relatively high levels of resistance to most insecticides available for their control. However, of these two species H. virescens has emerged as the predominant pest on cotton. The status of H. virescens may be due, at least in part, to its lower susceptibility to most insecticides relative to H. zea (Table 1). This reduced susceptibility is the result of inherently higher levels of detoxifying enzyme activity (Plapp 1973, Reed 1974, Bigley and Plapp 1978). Perhaps the innate tolerance of H. virescens toward most insecticides may partially explain why the composition of the Heliothis complex on cotton during the late season in Louisiana, as well as other areas, has shifted from primarily H. zea to H. virescens (Clower et al. 1975, Graves and Clower 1975, Mayeux 1976, Roussel 1976). Thus, because H. virescens is inherently less susceptible to insecticides than H. zea, and because of its predominance during the late season, it now presents one of the major problems in cotton insect control.