Abstract 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.

中文翻译：

---

应用选择实验来测试西部玉米根虫（鞘翅目：Chrysomelidae）中 Bt 抗性的适应成本和密度对适应成本的影响

摘要 西方玉米根虫 Diabrotica virgifera virgifera LeConte 是一种严重的玉米害虫，通常使用产生来自苏云金芽孢杆菌 (Bt) 的杀虫毒素的转基因玉米进行管理。 这种害虫已经对所有市售 Bt 性状产生了田间进化的抗性，从 2009 年的 Cry3Bb1 开始。健身成本可能伴随着 Bt 抗性，与 Bt 易感个体相比，具有 Bt 抗性等位基因的个体对非 Bt 玉米的适应度降低。结合非 Bt 避难所，健身成本可以延迟 Bt 抗性的演变。重要的是，生态因素可能会影响健身成本的存在和大小。对于西部玉米根虫，现有数据表明在某些情况下可能存在 Bt 抗性的适应成本。使用两种抗 Cry3Bb1 的西部玉米根虫品系（Hopkinton 和 Cresco），通过在没有 Bt 的情况下饲养根虫六代进行适应性成本实验，以测试 Cry3Bb1 抗性的适应性成本和幼虫饲养密度对适应性的影响成本。检测到两种菌株的健身成本；然而，在实验结束时，菌株仍然对 Cry3Bb1 玉米具有抗性。Cresco 在低密度与高密度下经历了更大的阻力损失，但在霍普金顿没有检测到密度的影响。我们的研究表明，适应成本可能伴随着西部玉米根虫的 Bt 抗性，并且在低幼虫密度下可能更为明显。尽管存在健康成本，但似乎根虫种群在抗性进化后仍可能对 Cry3Bb1 玉米保持抗性多年。