Department of Entomology, Iowa State University, Ames, IA.
J Econ Entomol. 2020 Oct 16;113(5):2473-2479. doi: 10.1093/jee/toaa168.
Western corn rootworm, Diabrotica virgifera virgifera LeConte, is a serious pest of corn and is often managed with transgenic corn producing insecticidal toxins from the bacterium Bacillus thuringiensis (Bt). This pest has developed field-evolved resistance to all commercially available Bt traits, beginning with Cry3Bb1 in 2009. Fitness costs may accompany Bt resistance, where individuals with alleles for Bt resistance have reduced fitness on non-Bt corn compared to Bt-susceptible individuals. In conjunction with non-Bt refuges, fitness costs can delay the evolution of Bt resistance. Importantly, ecological factors may affect the presence and magnitude of fitness costs. For western corn rootworm, available data suggest that fitness costs of Bt resistance may be present in some cases. Using two Cry3Bb1-resistant western corn rootworm strains (Hopkinton and Cresco), a fitness-cost experiment was performed by rearing rootworm in the absence of Bt for six generations to test for fitness costs of Cry3Bb1 resistance and the effect of larval rearing density on fitness costs. Fitness costs were detected for both strains; however, strains were still resistant to Cry3Bb1 corn at the end of the experiment. Cresco experienced a greater loss of resistance at low versus high density, but no effect of density was detected in Hopkinton. Our study shows that fitness costs can accompany Bt resistance in western corn rootworm and may be more pronounced under low larval density. Even though fitness costs were present, it appears that rootworm populations may remain resistant to Cry3Bb1 corn for years after resistance has evolved.
西方玉米根萤叶甲，Diabrotica virgifera virgifera LeConte，是玉米的一种严重害虫，通常通过种植产生来自苏云金芽孢杆菌（Bt）杀虫毒素的转基因玉米来加以管理。自 2009 年以来，这种害虫已对所有商业上可用的 Bt 特性产生了田间进化抗性，首先是 Cry3Bb1。Bt 抗性可能伴随着适应度代价，即具有 Bt 抗性等位基因的个体在非 Bt 玉米上的适应度比 Bt 敏感个体低。与非 Bt 避难所一起，适应度代价可以延缓 Bt 抗性的进化。重要的是，生态因素可能会影响适应度代价的存在和程度。对于西方玉米根萤叶甲，现有数据表明，在某些情况下，Bt 抗性的适应度代价可能存在。使用两种 Cry3Bb1 抗性的西方玉米根萤叶甲品系（Hopkinton 和 Cresco），通过在无 Bt 的情况下连续饲养 6 代来进行适应度代价实验，以测试 Cry3Bb1 抗性的适应度代价以及幼虫饲养密度对适应度代价的影响。两种品系均检测到适应度代价；然而，在实验结束时，两种品系对 Cry3Bb1 玉米仍具有抗性。与高密度相比，Cresco 在低密度下抗性损失更大，但在 Hopkinton 中未检测到密度的影响。我们的研究表明，适应度代价可能伴随着西方玉米根萤叶甲的 Bt 抗性，并且在幼虫密度较低时可能更为明显。即使存在适应度代价，在抗性出现后，玉米根萤叶甲种群似乎仍能在多年内保持对 Cry3Bb1 玉米的抗性。
