Field-based assessment of resistance to Bt Corn by Western Corn Rootworm (Coleoptera: Chrysomelidae)

Authors: SHRESTHA, RAM - Iowa State University; JAKKA, SIVA - Iowa State University; French, Bryan; GASSMANN, AARON - Iowa State University

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2016
Publication Date: 4/27/2016
Citation: Shrestha, R.B., Jakka, S.R., French, B.W., Gassmann, A.J. 2016. Field-based assessment of resistance to Bt Corn by Western Corn Rootworm (Coleoptera: Chrysomelidae). Journal of Economic Entomology. 109(3):1399–1409. doi:10.1093/jee/tow087.

Interpretive Summary: Western corn rootworm (WCR) is a serious pest of corn and since 2003 has been managed with Bt corn, which kills WCR when ingested. In 2009 severe injury to Bt corn producing the Cry3Bb1 toxin was observed in some cornfields in Iowa, indicating some WCR populations were becoming resistant to corn producing Cry3Bb1. However, few data exist on how Cry3Bb1-resistant WCR interact with other management practices such as Bt corn producing the mCry3A toxin, and field-based comparisons between Cry3Bb1-resistant and Cry3Bb1-susceptible populations are rare. Using a field experiment, we found that WCR survival to adulthood and root injury to corn were significantly higher in problem-field populations than control populations for both Cry3Bb1 corn and mCry3A corn. Our results provide further evidence that western corn rootworm has developed resistance to Cry3Bb1 corn and mCry3A corn in some fields in Iowa. Our results will help in developing strategies for managing Cry3Bb1-resistant WCR populations, and delaying the additional evolution of Bt resistance by this pest.

Technical Abstract: Western corn rootworm, Diabrotica virgifera virgifera LeConte, is a serious pest of corn and is managed with Bt corn that produce insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt). Beginning in 2009, severe injury to Bt corn producing Cry3Bb1 was observed in some cornfields in Iowa, and that feeding injury was associated with Cry3Bb1 resistance. However, few data exist on how Cry3Bb1-resistant western corn rootworm interact with various management practices, and field-based comparisons between Cry3Bb1-resistant and Cry3Bb1- susceptible populations are rare. Using a field experiment, we measured survival to adulthood and feeding injury to corn roots for both Cry3Bb1-resistant and Cry3Bb1-susceptible populations of western corn rootworm when tested against various Bt corn hybrids and a soil-applied insecticide. We evaluated five fields where associated with greater than one node of feeding injury to Cry3Bb1 corn by western corn rootworm (i.e., problem-field populations). In both years, we also tested a laboratory strain of western corn rootworm that had never been exposed to Bt corn as a control population. Survival to adulthood for western corn rootworm and root injury to corn were significantly higher in problem-field populations than control populations for both Cry3Bb1 corn and mCry3A corn. Our results provide further evidence that western corn rootworm has developed resistance to Cry3Bb1 corn and mCry3A corn in some fields in Iowa. The results of this study are discussed in terms of developing strategies for managing Cry3Bb1-resistant western corn rootworm, and delaying the additional evolution of Bt resistance by this pest.