Helicoverpa zea and Bt Cotton in the United States

Abstract

Helicoverpa zea (Boddie), the bollworm or corn earworm, is the most important lepidopteran pest of Bt cotton in the United States. Corn is the preferred host, but the insect feeds on most flowering crops and wild host plants. As a cotton pest, bollworm has been closely linked to the insecticide-resistance prone Heliothis virescens (F.), tobacco budworm. Immature stages of the two species are difficult to separate in field environments. Tobacco budworm is very susceptible to most Bt toxins, and Bt cotton is considered to be "high dose." Bollworm is less susceptible to Bt toxins, and Bt cotton is not "high dose" for this pest. Bt cotton is routinely sprayed with traditional insecticides for bollworm control. Assays of bollworm field populations for susceptibility to Bt toxins expressed in Bt cotton have produced variable results since pre-deployment of Bt cottons in 1988 and 1992. Analyses of assay response trends have been used by others to suggest that field resistance has evolved to Bt toxins in bollworm, but disagreement exists on definitions of field resistance and confidence of variable assay results to project changes in susceptibility of field populations. Given historical variability in bollworm response to Bt toxins, erratic field control requiring supplemental insecticides since early field testing of Bt cottons, and dramatic increases in corn acreage in cotton growing areas of the Southern US, continued vigilance and concern for resistance evolution are warranted.

Revisiting macronutrient regulation in the polyphagous herbivore Helicoverpa zea (Lepidoptera: Noctuidae): New insights via nutritional geometry

“…Up-dating and providing a more accurate account of how H. zea responds to different nutritional environments also provides a stronger foundation for further exploring its physiology and nutritional ecology. For example, the use of more realistic artificial diets in laboratory studies can be used to standardize nutritional environments across different physiological experiments, or enhance the ecological relevance of applied studies such as diet-based resistance monitoring programs (e.g., Ali et al, 2006;Luttrell and Jackson, 2012). (Lee et al, 2004a), H. virescens (Lee et al, 2006;Telang et al, 2001;Roeder and Behmer, 2014), S. litura (Lee, 2010), as well as the ITs for H. zea reported by Waldbauer et al (1984) and this study.…”

Defining Terms for Proactive Management of Resistance to Bt Crops and Pesticides

“…Despite the results summarized above, some scientists have challenged the conclusion of practical resistance to Bt cotton in H. zea (Moar et al 2008, Luttrell and Jackson 2012, Sumerford et al 2013). One of their principal arguments is that the documentation relies on bioassays of insects collected from Bt crops (Moar et al 2008, Sumerford et al 2013).…”

Transgenic Bt Cotton: Effects on Target and Non-Target Insect Diversity

“…GM cotton expressing Cry genes is cultivated on 33.1 million ha in different cotton growing countries including United States [16,17], China [18][19][20], India [21][22][23][24][25][26], South Africa [27][28][29], Mexico [30], Argentina [31,32] and Pakistan [33][34][35][36][37][38][39][40][41][42][43] and experienced many benefits like reduced use of broad-spectrum insecticides, improved control of target pests, reduced production cost, increased yield and better opportunity for biological control.…”