Fitness costs of resistance to Cry3Bb1 maize by western corn rootworm

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), which is a significant pest of maize in the United States and Europe. However, the widespread use of Bt maize places intense selection pressure on pest populations to evolve resistance, and field-evolved resistance to Bt maize by western corn rootworm has been documented in the United States. In conjunction with non-Bt refuges, fitness costs of Bt resistance can delay resistance evolution. Fitness costs arise in the absence of Bt toxin when individuals with resistance alleles have lower fitness than Btsusceptible genotypes. We quantified the level of resistance and fitness costs of resistance for a strain of western corn rootworm with laboratoryselected resistance to transgenic maize (Zea mays L.) producing Bt toxin Cry3Bb1. Survival to adulthood on Cry3Bb1 maize was more than twofold higher for resistant insects vs. susceptible insects, which is similar to the magnitude of resistance first observed in the field. Fitness costs were measured in two experiments; the first used maize hybrids and the second used inbred lines. The experiment with maize hybrids compared resistant and susceptible strains while the experiment with maize inbreds compared resistant, susceptible and heterozygous genotypes. The only nonrecessive fitness cost detected (i.e. cost affecting heterozygotes) was for adult size. Recessive fitness costs (i.e. costs affecting the resistant strain) were observed for developmental rate, female survival and egg viability. However, when reared on non-Bt maize, the resistant strain also displayed higher fecundity, higher survival for males and greater adult longevity compared to the susceptible strain. These results suggest that resistance to Bt maize by western corn rootworm may not impose substantial fitness costs, and consequently, may evolve quickly and persist once present.

Measuring rootworm refuge function: Diabrotica virgifera virgifera emergence and mating in seed blend and strip refuges for Bacillus thuringiensis (Bt) maize

“…Other studies have shown that larvae feeding only on Cry3Bb1-expressing plants develop into smaller adults. 12,13,27 It is possible that size similarities in our study resulted from larvae moving between refuge and Bt plants [28][29][30] or that there were no effects on size from Cry toxin feeding, as observed in some WCR populations. 11,29,31 Emergence timing may also influence mate selection.…”

Effects of adult emergence timing on susceptibility and fitness of Cry3Bb1‐resistant western corn rootworms

“…; Hoffmann et al. ). Hence, more studies are needed to characterize field‐evolved WCR‐resistant populations (Hoffmann et al.…”

“…Hence, more studies are needed to characterize field‐evolved WCR‐resistant populations (Hoffmann et al. ; Ingber and Gassmann ), and especially, studies were conducted to evaluate the current spatial variability in susceptibility of populations to Bt traits to determine the type of environment current and future technologies will be deployed in agroecosystems.…”

“…This study provides data from additional resistant field collections and shows that geographical variation in WCR lifehistory parameters can occur on relatively small spatial or temporal scales after dietary exposure to Cry3Bb1. Most published studies on Cry3Bb1 resistance have been conducted with laboratory-selected WCR colonies (Meihls et al 2008(Meihls et al , 2012Oswald et al 2011Oswald et al , 2012Petzold-Maxwell et al 2012;Hoffmann et al 2015). Hence, more studies are needed to characterize field-evolved WCR-resistant populations (Hoffmann et al 2015;Ingber and Gassmann 2015), and especially, studies were conducted to evaluate the current spatial variability in susceptibility of populations to Bt traits to determine the type of environment current and future technologies will be deployed in agroecosystems.…”

A P-Glycoprotein Is Linked to Resistance to the Bacillus thuringiensis Cry3Aa Toxin in a Leaf Beetle

“…Studies with Cry3Bb1-resistant laboratory strains of D. virgifera feeding on non-transgenic maize showed either a fitness benefit [42] or costs and benefits in different fitness components [43]. In experiments with the Bar-le-Duc-resistant strain of C. tremula studied by Wenes et al [27], the frequency of the recessive resistant allele declined from 0.5 to 0.179 over five generations of rearing on non-Bt poplar, indicating a fitness cost of resistance.…”