Abstract
Insecticidal toxins from Bacillus thuringiensis (Bt) are valuable tools for pest management worldwide, contributing to the management of human disease insect vectors and phytophagous insect pests of agriculture and forestry. Here, we report the effects of dual and triple Bt toxins expressed in transgenic cotton cultivars on the fitness and demographic performance of Helicoverpa zea (Boddie)—a noctuid pest, known as cotton bollworm and corn earworm. Life-history traits were determined for individuals of three field populations from a region where H. zea overwintering is likely. Triple-gene Bt cotton cultivars that express Cry and Vip3Aa toxins killed 100% of the larvae in all populations tested. In contrast, dual-gene Bt cotton that express Cry1Ac+Cry1F and Cry1Ac+Cry2Ab allowed population growth with the intrinsic rate of population growth (rm) 38% lower than on non-Bt cotton. The insects feeding on Bt cotton plants that express Cry1Ac+Cry2Ab, Cry1Ac+Cry1F, or Cry1Ab+Cry2Ae exhibited reduced larval weight, survival rate, and increased development time. Additionally, fitness parameters varied significantly among the insect populations, even on non-Bt cotton plants, likely because of their different genetic background and/or previous Bt toxin exposure. This is the first report of the comparative fitness of H. zea field populations on dual-gene Bt cotton after the recent reports of field resistance to certain Bt toxins. These results document the population growth rates of H. zea from an agricultural landscape with 100% Bt cotton cultivars. Our results will contribute to the development and validation of resistance management recommendations.
Highlights
Transgenic crops that express insecticidal toxins from the bacterium Bacillus thuringiensis (Berliner)(Bt) provide valuable pest management options for pests of field crops worldwide [1,2,3]
Panhandle varied among cotton cultivars and field populations, indicating differences among the Panhandle varied among cotton cultivars and field populations, indicating differences among the cultivars in the efficacy against H. zea and the current population susceptibility to the Bt toxins
The effects on immature insect fitness components both population and cotton cultivar translated to negative effects on the growth potential of H. zea
Summary
Transgenic crops that express insecticidal toxins from the bacterium Bacillus thuringiensis (Berliner). (Bt) provide valuable pest management options for pests of field crops worldwide [1,2,3]. Positive socio-economic and environmental impacts of Bt crop adoption have been reported since commercial release in 1996 [4,5]. Toxins 2020, 12, 551 cotton pests Chloridea virescens (Fabricius) (Lepidoptera: Noctuidae), Pectinophora gossypiella (Saunders). Bt cotton improves the management of other lepidopteran pests, such as Spodoptera exigua (Hübner), Trichoplusia ni (Hübner), Spodoptera frugiperda (J.E. Smith), S. eridania (Stoll), and Chrysodeixis includens (Walker) [8,9,10,11]. From 1996–2003, commercial Bt cotton in the U.S was limited to events that expressed the Cry1Ac toxin [12]. Second generation dual-gene Bt cotton that expressed the toxins
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