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ARS Home » Plains Area » Brookings, South Dakota » Integrated Cropping Systems Research » Research » Publications at this Location » Publication #294934
Title: Fitness costs of resistance to Cry3Bb1 maize by Western Corn Rootworm

Author
item HOFFMANN, AMANDA - Iowa State University
item French, Bryan
item Hellmich Ii, Richard
item Lauter, Nicholas
item GASSMANN, AARON - Iowa State University

Submitted to: Journal of Applied Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2014
Publication Date: 1/29/2015
Citation: Hoffmann, A.M., French, B.W., Hellmich II, R.L., Lauter, N.C., Gassmann, A.J. 2015. Fitness costs of resistance to Cry3Bb1 maize by Western Corn Rootworm. Journal of Applied Entomology. 139(6):403-415. DOI:10.1111/jen.12209.

Interpretive Summary: Crops producing Bt toxins are widely planted to manage insect pests, including western corn rootworm (WCR) beetles, a very important pest of corn. However, increased survival or resistance on Bt plants would diminish the effectiveness of this technology, unless this increased survival is somehow delayed. We determined relative survivorship and tested for costs associated with resistance in WCR. Survival on Bt corn was over twice as high for resistant insects versus susceptible insects. Two experiments then were conducted with non-Bt corn, the first used three commercial hybrids and the second used three inbred lines. The experiment with commercial hybrids compared resistant and susceptible WCR strains and the experiment with inbred lines compared resistant and susceptible WCR strains as well as offspring from matings between resistant and susceptible individuals, which we also tested for non-recessive fitness costs. The only non-recessive fitness cost detected was an additive fitness cost affecting adult size. Recessive fitness costs were observed for developmental rate, female survival, and egg viability. However, fitness benefits of higher fecundity, higher male survival, and greater longevity were detected for the resistant strain in the absence of Bt corn. Overall the average difference between resistant and susceptible strains, in the absence of Bt corn, was a 5.3% benefit for resistant insects. These results suggest that resistance to certain Bt corn hybrids by western corn rootworm may not impose fitness costs, and consequently, may evolve quickly and persist once present.

Technical Abstract: Crops producing toxins derived from the bacterium Bacillus thuringiensis (Bt) are widely planted to manage insect pests, including western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), a significant pest of maize. The evolution of resistance would diminish the effectiveness of this technology; however, fitness costs can delay resistance. We quantified the level of resistance and tested for fitness costs of resistance in western corn rootworm with resistance to transgenic maize (Zea mays L.) that produces the Bt toxin Cry3Bb1. Survival on Cry3Bb1 maize was more than twice as high for resistant insects versus susceptible insects. Fitness costs were measured in two experiments with non-Bt maize, the first used three commercial hybrids and the second used three inbred lines. The experiment with commercial hybrids compared resistant and susceptible strains and the experiment with maize inbreds also included heterozygous individuals and tested for non-recessive fitness costs. The only non-recessive fitness cost detected was an additive fitness cost affecting adult size. Recessive fitness costs were observed for developmental rate, female survival, and egg viability. However, fitness benefits of higher fecundity, higher male survival, and greater longevity were detected for the resistant strain in the absence of Bt maize. Including all statistically significant fitness costs and benefits, the average difference between strains, in the absence of Bt maize, was a 5.3% fitness benefit for resistant insects. These results suggest that resistance to Bt maize by western corn rootworm may not impose fitness costs, and consequently, may evolve quickly and persist once present.