|PETZOLD-MAXWELL, JENNIFER - Iowa State University|
|CLIFTON, ERIC - Iowa State University|
|DUNBAR, MIKE - Iowa State University|
|GASSMAN, AARON - Iowa State University|
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2012
Publication Date: 4/1/2013
Publication URL: http://handle.nal.usda.gov/10113/56100
Citation: Petzold-Maxwell, J., Jaronski, S., Clifton, E.H., Dunbar, M.W., Jackson, M.A., Gassman, A.J. 2013. Interactions among Bt maize, entomopathogens, and rootworm species (Coleoptera: Chrysomelidae) in the field: effects on survival, yield and root injury. Journal of Economic Entomology. 106(2): 622-632.
Interpretive Summary: Maize, genetically transformed to express the insect-toxic proteins of Bacillus thuringiensis to control the European corn borer and the Western and Northern Corn Rootworms, has become a mainstay in U.S. corn agriculture, and also significant in a number of other countries. These insect pests do have natural microbial and nematode enemies, which could have a significant control role if/when pest resistance to Bt-maize becomes important, as well as complement its use to forestall resistance to Bt. Yet the interaction between Bt-maize and these control agents has not been evaluated. In this two-year field study, supplementing a previously published laboratory and greenhouse evaluation, involving one Bt-maize line, the insect pathogenic fungus Metarhizium brunneum and the insect attacking nematodes, Heterorhabditis bacteriophora, and Steinernema carpocapsae, were used as a model system. While yield was significantly increased by the addition of entomopathogens to the soil, the survival of the corn rootworm species was not affected. 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.
Technical Abstract: 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.