Assessing the single and combined toxicity of the bioinsecticide spear and cry3Bb1 protein against susceptible and resistant western corn rootworm larvae (coleoptera: chrysomelidae)

Authors: PEREIRA, ADRIANO - University Of Missouri; HUYNH, MAN - University Of Missouri; CARLSON, A - Vestaron Corporation; HAASE, A - Vestaron Corporation; KENNEDY, ROBERT - Vestaron Corporation; Shelby, Kent; Coudron, Thomas; Hibbard, Bruce

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/27/2021
Publication Date: 8/28/2021
Citation: Pereira, A.E., Huynh, M.P., Carlson, A.R., Haase, A., Kennedy, R.M., Shelby, K., Coudron, T.A., Hibbard, B.E. 2021. Assessing the single and combined toxicity of the bioinsecticide spear and cry3Bb1 protein against susceptible and resistant western corn rootworm larvae (coleoptera: chrysomelidae). Journal of Economic Entomology. 114(5):2220–2228. https://doi.org/10.1093/jee/toab160.
DOI: https://doi.org/10.1093/jee/toab160

Interpretive Summary: Corn rootworms are a major threat to corn growers in the U.S. Corn Belt. Rootworms have developed resistance to nearly all management strategies including transgenic corn expressing toxins from the soil bacterium, Bacillus thuringiensis (Bt). Thus new corn management tactics are needed to manage rootworms. In this study, we evaluated the susceptibility of rootworm strains resistant and susceptible to Bt the biological insecticide Spear®-T, alone and combination with Bt protein. In this study, the biological insecticide Spear®, derived from the Australian funnel web spider venom was documented to be insecticidal against WCR larvae with no apparent cross-resistance with Bt. In low concentration together with Bt protein, Spear® clearly enhanced the effect of Bt protein against resistant WCR larvae. Growers will benefit from development of new rootworm control strategies such as Spear® that are not cross-resistant with currently used insecticides and Bt proteins.

Technical Abstract: The western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), poses serious threat to maize (Zea mays L.) growers in the U.S. Corn Belt. Transgenic corn expressing Bacillus thuringiensis (Bt) is the major management tactic along with crop rotation. Bt crops targeting WCR populations have been widely planted throughout the Corn Belt. Rootworms have developed resistance to nearly all management strategies including Bt corn. Therefore, there is a need for new products that are not cross-resistant with the current Bt proteins. In this study, we evaluated the susceptibility of WCR strains resistant and susceptible to Cry3Bb1 to the biological insecticide Spear®-T (GS-omega/kappa-Hexatoxin-Hv1a) alone and combined with Cry3Bb1 protein. The activity of Spear® alone was similar between Cry3Bb1-resistant and susceptible strains (LC50s= 0.95 mg/cm2 and 1.50 mg/cm2, respectively), suggesting that there is no cross-resistance with Cry3Bb1 protein. Effective concentration (EC50), molt inhibition concentration (MIC50), and inhibition concentration (IC50) values of Spear® alone were also similar between both strains, based on non-overlapping confidence intervals. Increased mortality (64%) was observed on resistant larvae exposed to Spear® (0.6 mg/cm2) + Cry3Bb1 protein (170.8 µg/cm2) compared to 0% mortality when exposed to Cry3Bb1 alone and 34% mortality to Spear® alone (0.3 mg/cm2). The time of larval death was not significantly different between Spear® alone (3.79 mg/cm2) and Spear® (0.6 mg/cm2) + Cry3Bb1 (170.8 µg/cm2). New control strategies that are not cross-resistant with current insecticides and Bt proteins are needed to better manage the WCR, and Spear® together with Cry3Bb1 may fit this role.