Assessment of Inheritance and Fitness Costs Associated with Field-Evolved Resistance to Cry3Bb1 Maize by Western Corn Rootworm

Abstract

The western corn rootworm, Diabrotica virgifera virgifera LeConte, is among the most serious insect pests of maize in North America. One strategy used to manage this pest is transgenic maize that produces one or more crystalline (Cry) toxins derived from the bacterium Bacillus thuringiensis (Bt). To delay Bt resistance by insect pests, refuges of non-Bt maize are grown in conjunction with Bt maize. Two factors influencing the success of the refuge strategy to delay resistance are the inheritance of resistance and fitness costs, with greater delays in resistance expected when inheritance of resistance is recessive and fitness costs are present. We measured inheritance and fitness costs of resistance for two strains of western corn rootworm with field-evolved resistance to Cry3Bb1 maize. Plant-based and diet-based bioassays revealed that the inheritance of resistance was non-recessive. In a greenhouse experiment, in which larvae were reared on whole maize plants in field soil, no fitness costs of resistance were detected. In a laboratory experiment, in which larvae experienced intraspecific and interspecific competition for food, a fitness cost of delayed larval development was identified, however, no other fitness costs were found. These findings of non-recessive inheritance of resistance and minimal fitness costs, highlight the potential for the rapid evolution of resistance to Cry3Bb1 maize by western corn rootworm, and may help to improve resistance management strategies for this pest.

Western corn rootworm abundance, injury to corn, and resistance to Cry3Bb1 in the local landscape of previous problem fields

“…Examples include European corn borer, Ostrinia nubilalis , pink bollworm, Pectinophora gossypiella , and tobacco budworm, Heliothis virescens [ 44 – 46 ]. Western corn rootworm, however, experience minor fitness costs of Bt resistance, are managed with Bt traits that do not meet the threshold for high-dose, and appear to have high initial frequency for Bt-resistance traits [ 32 , 35 , 47 , 48 ]. Thus, this pest is well-suited for adaptation to Bt and field-level selection may lead to rapid resistance evolution.…”

“…A model developed by Sisterson et al [ 15 ] showed that Bt resistance can develop rapidly when resistance is non-recessive, irrespective of movement rate among fields. This may be of relevance to western corn rootworm, which exhibits non-recessive inheritance of resistance alleles [ 48 ]. Thus, further research in this area may be necessary to fully elucidate the relationship between field-evolved Bt resistance and movement in the landscape by western corn rootworm.…”

“…Resulting larvae were used in a single-plant bioassay following Gassmann et al [18]. The bioassay consisted of 12 replicates of two corn types, Bt (Cry3Bb1 [DKC [43][44][45][46][47][48] and its non-Bt genetic isoline [DKC [43][44][45][46]). Plants were grown in 1 L plastic cups (Placon, Madison, WI) to the V4-V5 growth stage [40].…”

Resistance to Bt Maize by Western Corn Rootworm: Effects of Pest Biology, the Pest–Crop Interaction and the Agricultural Landscape on Resistance

“…Research on strains with field-evolved resistance to Cry3Bb1 maize also found evidence of non-recessive inheritance resistance [ 65 , 66 , 67 ] ( Table 1 ). In three of four strains, where field-evolved resistance had been introgressed into a non-diapausing background, resistance to Cry3Bb1 maize was found to be non-recessive [ 65 , 66 ].…”

Editorial for Special Issue: The Insecticidal Bacterial Toxins in Modern Agriculture

“…The results showed no cross-resistance in four Cry1Ac and Cry2Aa resistant populations indicating that Vip3A is a good alternative for the Cry proteins. In another paper, Paolino and Gassmann [ 6 ] analyzed two strains of the coleopteran Diabrotica virgifera virgifera (Western Corn Rootworm, WCR) with field-evolved resistance to Cry3Bb1 maize. Using plant-based and diet-based bioassays, the authors revealed that the inheritance of resistance was non-recessive and had no fitness costs associated.…”