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Interactions Among Bt Maize, Entomopathogens, and Rootworm Species (Coleoptera: Chrysomelidae) in the Field: Effects on Survival, Yield and Root Injury

Petzold-Maxwell, Jennifer L., Jaronski, Stefan T., Clifton, Eric H., Dunbar, Mike W., Jackson, Mark A., Gassmann, Aaron J.
Journal of economic entomology 2013 v.106 no.2 pp. 622-632
Bacillus thuringiensis, Diabrotica barberi, Diabrotica virgifera virgifera, Heterorhabditis bacteriophora, Metarhizium brunneum, Steinernema carpocapsae, Zea mays, bacterial proteins, bacterial toxins, biological control, corn, crop yield, crystal proteins, delta-endotoxins, entomopathogenic fungi, entomopathogenic nematodes, insect control, insecticidal proteins, plant damage, population dynamics, roots, survival rate
A two year field study was conducted to determine how a blend of entomopathogens interacts with Bt maize to affect survival of corn rootworm (Diabrotica spp.) species and performance of maize (Zea maize L.). The blend of entomopathogens included two entomopathogenic nematodes, Steinernema carpocapsae Weiser and Heterorhabditis bacteriophora Poinar, and one entomopathogenic fungus, Metarhizium brunneum (Metschnikoff) Sorokin. Bt maize (event 59122, which produces Bt toxin Cry34/35Ab1) decreased root injury and survival of western (Diabrotica virgifera virgifera Le Conte) and northern (Diabrotica barberi Smith & Lawrence) corn rootworm, but did not affect yield. During year one of the study, when natural rootworm abundance was high, entomopathogens in combination with Bt maize led to a significant reduction in root injury. In year two of the study, when rootworm abundance was lower, entomopathogens significantly decreased injury to non-Bt maize roots, but had no effect on Bt maize roots. Using the combined data from both years, yield was significantly increased by the addition of entomopathogens to the soil. Entomopathogens did not decrease survival of corn rootworm species in either year of the study, and did not have a consistent or direct effect on the timing of corn rootworm emergence. The results suggest that soil-borne entomopathogens can complement Bt maize in protecting roots from rootworm injury when rootworm abundance is high, and can be beneficial to non-Bt maize when abundance is low. In addition, this study also showed that the additions of entomopathogens to soil contributed to an overall increase in yield.