Evaluation of GS-omega/kappa-Hxtx-Hv1a and Bt toxins against Bt-resistant and -susceptible strains of Helicoverpa zea (Boddie) and Spodoptera frugiperda (J.E. Smith)

BACKGROUND: Helicoverpa zea and Spodoptera frugiperda are destructive insect pests of cotton and corn. Both have evolved practical resistance to transgenic crops producing Bacillus thuringiensis (Bt) toxins in the United States. GS-omega/kappa-Hxtx-Hv1a (ω/κ-Hv1a) is a novel biopesticide derived from spider venom with activity against lepidopteran pests. The efficacy of ω/κ-Hv1a is dependent on combining it with a facilitator product such as a Bt-based insecticide. However, it is unknown if ω/κ-Hv1a can be an alternative for the management of Bt resistance. In this study, we tested the effect of ω/κ-Hv1a alone or in the presence of Bt toxins against susceptible and resistant H. zea and S. frugiperda. RESULTS: Diet overlays with 5 μg cm⁻² of Vip3Aa39 significantly increased mortality in susceptible H. zea but did not enhance the activity of ω/κ-Hv1a against Vip3A-resistant H. zea. In contrast, the addition of 10 μg cm⁻² of Cry1Ac to the surface of ω/κ-Hv1a incorporated diet significantly increased the mortality of Cry-resistant H. zea compared to diets without the Cry1Ac toxin. CONCLUSION: The study confirms that ω/κ-Hv1a activity against H. zea is significantly enhanced by a facilitator mechanism. Our results suggest Cry1Ac pore formation in the midgut membrane of Cry-resistant H. zea, enables the activity of ω/κ-Hv1a. Vip3Aa resistance in H. zea involves altered toxin-binding, consequently preventing pore formation and activity of ω/κ-Hv1a. Therefore, insecticides containing ω/κ-Hv1a may be an alternative for managing Cry-resistant H. zea in cotton and help delay the evolution of insect resistance.