Effectiveness of microbial and chemical insecticides for supplemental control of bollworm on Bt and non-Bt cottons

Authors: Little, Nathan; Luttrell, Randall; Allen, Clint; Perera, Omaththage; Parys, Katherine

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2016
Publication Date: 3/18/2017
Citation: Little, N., Luttrell, R.G., Allen, K.C., Perera, O.P., Parys, K.A. 2017. Effectiveness of microbial and chemical insecticides for supplemental control of bollworm on Bt and non-Bt cottons. Journal of Economic Entomology. 110(3):1039-1051. doi:10.1093/jee/tow323.

Interpretive Summary: This manuscript assesses the potential for a commercially formulated microbial insecticide to suppress bollworm larvae in non-Bt and Bt cotton in supplemental control situations. Laboratory assays were used to determine bollworm survival on non-Bt and Bt cotton leaves treated with two microbial and two synthetic insecticides. Cotton leaves were also treated in the field, removed at regular time intervals, and brought into the laboratory for use in bioassays with bollworms to determine insecticide persistence. A two year field study was conducted to ascertain performance of microbial insecticides in a production-type setting. The quantitative estimates of insect mortality and field performance of microbial and chemical insecticides on non-Bt and Bt cottons may be useful in estimating the value of various insect management options and the threat of future resistance problems in the MS Delta.

Technical Abstract: Laboratory and field experiments were conducted to determine the effectiveness of microbial and chemical insecticides for supplemental control of bollworm (Helicoverpa zea Boddie) on non-Bt (DP1441®) and Bt (DP1321®) cottons. Neonate and 3rd instar larvae survival were evaluated on leaf tissue treated with microbial and chemical insecticides including a commercial formulation of Bacillus thuringiensis (Dipel®), a Heliothis (Helicoverpa) nuclear polyhedrosis virus (NPV) (Gemstar®), '-cyhalothrin (Karate Z®), and chlorantraniliprole (Prevathon®). Residual activity of insecticides was measured in a small plot field experiment. Microbial insecticides, with the exception of a mid-rate of Dipel with neonate larvae, performed comparable to chemical treatments on non-Bt cotton leaves with regard to 1st and 3rd instar bollworm mortality at 10 d and pupal eclosure at 20 d posttreatment. Production level field evaluations of supplemental bollworm control in non-Bt and Bt cottons with NPV, '-cyhalothrin, and chlorantraniliprole were also conducted. During both years of the field study, all chemical and microbial treatments were successful in suppressing bollworm larval densities in non-Bt cotton below economic threshold levels. Overall, net returns above bollworm control, regardless of treatment, were negatively correlated with larval abundance and plant damage. Additionally, there was no economic benefit to supplemental control of bollworms in Bt cotton at the larval densities observed during this study. These data provide benchmark comparisons for insect resistance management with microbial and chemical insecticides in Bt and non-Bt cottons and strategic optimization of the need to spray non-Bt and Bt cotton in IRM programs.