Fitness costs associated with Cry1F resistance in the European corn borer

Authors: PETZOLD-MAXWELL, JENNIFER - Iowa State University; SIEGFRIED, BLAIR - University Of Nebraska; Hellmich Ii, Richard; Abel, Craig; Coates, Brad; SPENCER, TERRENCE - University Of Nebraska; HORIKOSHI, RENATO - Iowa State University; GASSMANN, AARON - Iowa State University

Submitted to: Journal of Applied Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/27/2016
Publication Date: 2/23/2017
Citation: Petzold-Maxwell, J.L., Siegfried, B.D., Hellmich II, R.L., Abel, C.A., Coates, B.S., Spencer, T.A., Horikoshi, R.J., Gassmann, A.J. 2017. Fitness costs associated with Cry1F resistance in the European corn borer. Journal of Applied Entomology. 141(1-2):67-79. doi:10.1111/jen.12356.

Interpretive Summary: Genetically-engineered crops are widely planted to manage a number of insect pests; but there are concerns that insects will evolve resistance to these crops. Fitness costs associated with insect resistance are important to understand because, if they occur, they can delay the evolution of resistance. Ecological factors including host plant variety can affect the magnitude of fitness costs, and consequently, the degree to which fitness costs delay resistance. In this study, ARS scientists and university collaborators measured fitness costs of resistance to Bacillus thuringiensis (Bt) toxin Cry1F in the important maize pest, European corn borer. Fitness costs were shown not to be different between post-diapause and non-diapause European corn borer that fed on three lines of corn. A different experiment demonstrated that Cry1F resistant female European corn borer may produce fewer eggs compared to susceptible or hybrid counterparts, indicating that this fitness cost is recessive. Reduced egg laying of Cry1F resistant moths may reduce their relative reproductive rates, and impose a selective disadvantage to Bt resistant phenotypes that may contribute to maintenance of overall susceptibilities within European corn borer populations. This information is valuable to maize growers and scientists interested in delaying insect resistance to Bt maize.

Technical Abstract: Crops producing insecticidal toxins derived from the soil bacterium Bacillus thuringiensis (Bt) are widely planted in order to manage key insect pests. Bt crops can provide an effective tool for pest management; however, the evolution of Bt resistance can diminish this benefit. The European corn borer, Ostrinia nubilalis Hübner, is a significant pest of maize, and is widely managed with Bt maize in the Midwest of the United States. When Bt crops are grown in conjunction with non-Bt refuges, fitness costs of Bt resistance can delay the evolution of resistance. Importantly, fitness costs often vary with ecological factors, including host-plant genotype and diapause. In this study, we examined fitness costs associated with Cry1F resistance in O. nubilalis when insects were reared on three maize lines. Fitness costs were tested in two experiments. One experiment assessed the fitness costs of tested Cry1F-resistant and Cry1F-susceptible insects that were reared on plants as post-diapause larvae and experienced diapause. The second experiment tested resistant, susceptible and F1 heterozygotesus insects that were reared on plants but did not experience diapause. Despite larger size and greater adult longevity for Cry1F-resistant insects, these insects produced fewer fertile eggs than Cry1F-susceptible insects, and this occurred whether or not insects experienced independent of diapause. This fitness cost of reduced fecundity was not detected among in heterozygous individuals, which indicated that the fitness cost was recessive. Additionally, maize line did not affect the magnitude of this reduced fecundity cost. The lower fitness of Cry1F-resistant O. nubilalis may contribute to the maintenance of Cry1F susceptibility in field populations more than a decade after Cry1F maize was commercialized.