Response of Bt and Non-Bt Cottons to High Infestations of Bollworm (Helicoverpa zea Boddie) and Tobacco Budworm (Heliothis virescens (F.)) under Sprayed and Unsprayed Conditions

Allen Allen,Parys Parys,Luttrell Luttrell,Perera Perera,Little Little

doi:10.3390/agronomy9110759

Abstract

Early-maturing and full-season Bt and non-Bt cottons were exposed to high densities of tobacco budworm (Heliothis virescens (F.)) and bollworm (Helicoverpa zea Boddie) in 0.04 ha field cages during the summers of 2011 and 2012 to measure the possible need for supplemental use of insecticides on Bt cotton. Fruit survival within-season and at-harvest was carefully mapped on individual plants within comparative plots of all cottons untreated and sprayed with lambda-cyhalothin (0.0448 kg a.i./ha) or chlorantraniliprole (0.1009 kg a.i./ha) following insect infestations. Differences in lint yields among cotton maturity groups were not always detected, but early-maturing Bt cottons were among the higher yielding experimental plots for both years. Depending on the insecticide treatment, average harvested fruit ranged from 0.3 to 7.1 open bolls per plant for non-Bt cotton plots, while Bt cotton plots ranged from 1.8 to 7.5 open bolls per plant during the two-year study. Bt cottons generally protected fruit from insect damage and resulted in final yields comparable to those of insecticide sprayed Bt and non-Bt cottons. Unsprayed non-Bt cottons were significantly damaged by insects in these high-infestation environments.

Highlights

Cotton engineered to express insecticidal toxins from Bacillus thuringiensis (Bt) is arguably one of the greatest technical advancements in cotton insect control in United States history, perhaps comparable to the eradication of the boll weevil (Anthonomus grandis (Boheman)) [1]
In a previous review of Bt cotton refuge requirements, it was estimated that domestic benefits from Bt cotton adoption in the U.S was approximately 150 to 250 million USD [2]
These benefits were linked to increased yields and reductions in the usage of synthetic insecticides

Summary

Introduction

Cotton engineered to express insecticidal toxins from Bacillus thuringiensis (Bt) is arguably one of the greatest technical advancements in cotton insect control in United States history, perhaps comparable to the eradication of the boll weevil (Anthonomus grandis (Boheman)) [1]. While Bt cotton provides high-levels of control of tobacco budworm (Heliothis virescens (F.)) and pink bollworm (Pectinophora gossypiella (Saunders)), which dramatically reduced the impact of these key pests., susceptibility among the different insect species attacking cotton varies even to multiple-trait Bt cotton that expresses more than one Bt toxin [3,4,5]. It has provided economic control of bollworm (Helicoverpa zea Boddie) and suppression of various Spodoptera spp., but it has not eliminated problems from these lepidopteran pests. Bt cotton in some areas of the U.S, especially the Midsouth and Southeast, is routinely over-sprayed with insecticides (including the diamide and pyrethroid groups) to control bollworm [6]

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Conclusion