Effects of field history on resistance to Bt maize in western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae)

Authors: SHRESTHA, RAM - Iowa State University; DUNBAR, MIKE - Iowa State University; French, Bryan; GASSMANN, AARON - Iowa State University

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2018
Publication Date: 7/3/2018
Citation: Shrestha, R.B., Dunbar, M.W., French, B.W., Gassmann, A.J. 2018. Effects of field history on resistance to Bt maize in western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae). PLoS One. https://doi.org/10.1371/journal.pone.0200156.
DOI: https://doi.org/10.1371/journal.pone.0200156

Interpretive Summary: The western corn rootworm (WCR) is a serious pest of corn and has circumvented virtually all control measures, including the insecticidal protein Cry3Bb1. We assumed that the level of Cry3Bb1 resistance in populations of WCR could be affected by farming practices; specifically, field history. In 2013 and 2014, WCR were collected from four types of cornfields: 1) cornfields with a history of more than one node of root injury to Cry3Bb1 corn or mCry3A corn (past problem fields), 2) cornfields with more than one node of root injury to Cry3Bb1 corn or mCry3A corn at the time of sampling (current problem fields), 3) cornfields that were rotated to an alternative crop two years ago (rotated cornfields), and 4) cornfields that had been planted to corn continuously for more than seven years (continuous cornfields). Those field WCR populations along with seven Bt-susceptible control populations were tested for Cry3Bb1 resistance with both plant-based and diet-based bioassays. All field populations were resistant to Cry3Bb1 regardless of field history, however, some variation in the degree of resistance was found. For all categories of field populations, larval survivorship on Cry3Bb1 maize was significantly higher than control populations, and did not differ from survival on non-Bt maize. Evidence of resistance to Cry3Bb1 maize in plant-based bioassays was further supported by diet-based bioassays and we found a positive relationship between LC50 values from diet-based bioassays and the larval survivorship in plant-based bioassays. The results of this work will help to improve strategies for managing Bt resistance by WCR.

Technical Abstract: Western corn rootworm, Diabrotica virgifera virgifera LeConte, has evolved resistance to transgenic maize, Zea maize L., that produces the insecticidal protein Cry3Bb1, which is derived from the bacterium Bacillus thuringiensis. We hypothesized that the level of Cry3Bb1 resistance in populations of western corn rootworm could be influenced by farming practices. To test this hypothesis, we evaluated the effect of field history on resistance to Cry3Bb1 maize by western corn rootworm. In 2013 and 2014, western corn rootworm were collected from four types of maize fields: 1) maize fields with a history of more than one node of root injury to Cry3Bb1 maize or mCry3A maize (past problem fields), 2) maize fields with more than one node of root injury to Cry3Bb1 maize or mCry3A maize at the time of sampling (current problem fields), 3) maize fields that were rotated to an alternative crop two years ago (rotated maize fields), and 4) maize fields that had been planted to maize continuously for more than seven years (continuous maize fields). Those field populations along with seven Bt-susceptible control populations were tested for Cry3Bb1 resistance with both plant-based and diet-based bioassays. All field populations were resistant to Cry3Bb1 regardless of field history, however, some variation in the degree of resistance was found. For all categories of field populations, larval survivorship on Cry3Bb1 maize was significantly higher than control populations, and did not differ from survival on non-Bt maize. Evidence of resistance to Cry3Bb1 maize in plant-based bioassays was further supported by diet-based bioassays and we found a positive relationship between LC50 values from diet-based bioassays and the larval survivorship in plant-based bioassays. The results of this work will help to improve strategies for managing Bt resistance by western corn rootworm.