Department of Entomology, Iowa State University, Ames, Iowa, United States of America.
Corn Insects & Crop Genetics Research Unit, USDA-Agricultural Research Service, Ames, Iowa, United States of America.
PLoS One. 2019 Mar 1;14(3):e0212696. doi: 10.1371/journal.pone.0212696. eCollection 2019.
The western corn rootworm, Diabrotica virgifera virgifera (LeConte) (Coleoptera: Chrysomelidae), is an economically important pest of corn in the northern United States. Some populations have developed resistance to management strategies including transgenic corn that produces insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt). Knowledge of insect dispersal is of critical importance for models of resistance evolution. Larval density affects survival in the field, and stress from crowding often affects facultative long-distance dispersal of adult insects. In this study, we used laboratory flight mills to characterize western corn rootworm flight performance as a function of larval rearing density. Larvae were reared under three densities and the resulting adult females were either allowed to fly voluntarily for 22 h or forced to fly specified durations. For both experiments we also measured lifetime fecundity following flight. The three rearing densities placed differential levels of stress on individuals, as evidenced by decreased survival to adulthood and decreased size of adults at greater rearing density. When larvae were reared under crowded conditions the resulting females were more likely to engage in flight activity, including long uninterrupted flights lasting >10 min, than those reared under low density conditions. Flight and egg production are both energy intensive processes. However, we found no evidence in either voluntary or forced flight experiments of a tradeoff between flight activity and female fecundity. The results suggest that females emerging from high density populations in cornfields are more likely to disperse and disperse farther than those emerging from low density populations. These results are important because they imply that variation in population density in the landscape will affect dispersal, which may in turn require computer models of resistance evolution to incorporate multiple dispersal rates arising from varying larval densities among fields.
西方玉米根虫，Diabrotica virgifera virgifera (LeConte)（鞘翅目：金龟子科），是美国北部玉米的一种重要经济害虫。一些种群已经对包括转Bt 基因玉米在内的管理策略产生了抗性，Bt 基因来自苏云金芽孢杆菌。了解昆虫的扩散对于抗性进化模型至关重要。幼虫密度会影响田间存活率，拥挤带来的压力通常会影响成虫的非强制性远距离扩散。在本研究中，我们使用实验室飞行测功机来描述西方玉米根虫飞行性能与幼虫饲养密度的关系。幼虫在三种密度下饲养，然后让成年雌性自由飞行 22 小时或强制飞行特定时间。在这两个实验中，我们还测量了飞行后的终生繁殖力。三种饲养密度对个体造成了不同程度的压力，表现为存活率降低和成虫体型变小，饲养密度越高，个体压力越大。当幼虫在拥挤条件下饲养时，与在低密度条件下饲养的幼虫相比，产生的雌性更有可能进行飞行活动，包括持续时间超过 10 分钟的长而不间断的飞行。飞行和产卵都是能量密集型过程。然而，在自愿或强制飞行实验中，我们没有发现飞行活动和雌性繁殖力之间存在权衡的证据。结果表明，从玉米田中高密度种群中出现的雌性更有可能扩散，并且扩散得更远。这些结果很重要，因为它们意味着景观中种群密度的变化将影响扩散，这可能需要将多个来自不同田间的幼虫密度的扩散率纳入抗性进化的计算机模型中。
