Microbial insecticide application and evaluation: Cotton

Abstract

Microbial insecticides have been widely tested on cotton pests in the USA and other countries. Application of microbial insecticides to cotton has consisted primarily of evaluating Bacillus thuringiensis (Bt) and Helicoverpa zea nucleopolyhedrovirus (HzNPV) formulations. However, progress has also been made with entomopathogenic fungi, microsporidia, nematodes, and protozoa and these entomopathogens will also be considered in this chapter. Microbial insecticides on cotton were studied and developed, in part, in response to development of chemical insecticide resistance by heliothines. Introduction in the early 1980s of the highly efficacious and cost-effective pyrethroid insecticides curtailed development of microbial insecticides. However, resistance of Heliothis virescens to pyrethroids renewed interest in microbials (Plapp and Campanhola, 1986; Leonard et al., 1987; Luttrell et al., 1987), and widespread use of Bt products in tank mixtures with chemical insecticides against heliothines occurred in the 1990s in the southern USA prior to the introduction of transgenic cotton varieties containing a Bt toxin gene. Testing of microbial insecticides for cotton pests began in the 1960s (Ignoffo et al., 1965; Allen et al., 1966). Promising results from these and other similar tests were the impetus for widespread testing by industry in an effort to develop microbial pesticides against H. virescens and H. zea. By 1972, at least 28 tests had been conducted with HzNPV alone (Yearian and Young, 1978). Many field tests were also carried out with Bt, although these were usually industry sponsored and results were often not reported in the literature. A major effort on application of microbial insecticides on cotton continued into the early 1980s (Roome, 1975; Bell and Kanavel, 1977; Durant, 1977; Pieters et al., 1978; Luttrell et al., 1981, 1983; Johnson, 1982). In more recent years (late 1990s and 2000s) there has been a shift in emphasis from control of heliothines to control of sucking insect pests of cotton (Williams, 2004, 2005). This was in large part due to the introduction of Bt-cotton varieties reducing the need for chemical (or microbial) insecticides, the intro-