Faculty of Agriculture, KINDAI University, Nakamachi 3327-204, Nara, 631-8505, Japan.
Graduate School of Agriculture, KINDAI University, Nakamachi 3327-204, Nara, 631-8505, Japan.
Ecol Appl. 2019 Sep;29(6):e01945. doi: 10.1002/eap.1945. Epub 2019 Jul 24.
Indirect effects of agrochemicals on organisms via biotic interactions are less studied than direct chemical toxicity despite their potential relevance in agricultural landscapes. In particular, the role of species traits in characterizing indirect effects of pesticides has been largely overlooked. Moreover, it is still unclear whether such indirect effects on organisms are prevalent even when the organisms are exposed to direct toxicity. We conducted a mesocosm experiment to examine indirect effects of a herbicide (pentoxazone) on aquatic predatory insects of rice paddies. Because the herbicide selectively controls photosynthetic organisms, we assumed that the effects of the herbicide on predatory insects would be indirect. We hypothesized that phytophilous predators such as some Odonata larvae, which cling to aquatic macrophytes, would be more subject to negative indirect effects of the herbicide through a decrease in abundance of aquatic macrophytes than benthic, nektonic, and neustonic predators. Also, we crossed-applied an insecticide (fipronil) with herbicide application to examine whether the indirect effects of the herbicide on the assembling predators act additively with direct adverse effects of the insecticide. The herbicide application did not decrease the abundance of phytoplankton constitutively, and there were no clear negative impacts of the herbicide on zooplankton and prey insects (detritivores and herbivores). However, the abundance of aquatic macrophytes was significantly decreased by the herbicide application. Although indirect effects of the herbicide were not so strong on most predators, their magnitude and sign differed markedly among predator species. In particular, the abundance of phytophilous predators was more likely to decrease than that of benthic, nektonic, and neustonic predators when the herbicide was applied. However, these indirect effects of the herbicide could not be detected when the insecticide was also applied, seemingly due to fipronil's high lethal toxicity. Our study highlights the importance of species traits such as microhabitat use, which characterize biotic interactions, for predicting indirect effects of agrochemicals. Given that indirect effects of the chemicals vary in response to species traits and direct toxicity of other chemicals, efforts to explain this variation are needed to predict the realistic risks of indirect effects of agrochemicals in nature.
尽管生物相互作用对生物体的间接影响与直接化学毒性一样具有潜在的相关性，但它们在农业景观中的研究仍不如后者广泛。特别是，物种特征在描述农药间接影响方面的作用在很大程度上被忽视了。此外，即使生物体暴露于直接毒性之下，这种对生物体的间接影响是否普遍存在仍不清楚。我们进行了一项中观实验，以研究除草剂（戊氧唑）对稻田水生捕食性昆虫的间接影响。由于除草剂选择性地控制光合作用生物体，我们假设除草剂对捕食性昆虫的影响将是间接的。我们假设，像一些蜻蛉幼虫这样的嗜水性捕食者，由于水生植物丰度的减少，会受到除草剂负间接影响的影响更大，而底栖、游泳和漂浮的捕食者则不会。此外，我们交叉应用了杀虫剂（氟虫腈）和除草剂，以检验除草剂对聚集捕食者的间接影响是否与杀虫剂的直接不利影响相加。除草剂的应用并没有降低浮游植物的固有丰度，而且除草剂对浮游动物和猎物昆虫（碎屑食者和草食者）也没有明显的负面影响。然而，水生植物的丰度因除草剂的应用而显著下降。尽管除草剂对大多数捕食者的间接影响并不强烈，但它们的大小和方向在不同的捕食者物种之间有显著的差异。特别是，当除草剂应用时，嗜水性捕食者的丰度比底栖、游泳和漂浮的捕食者更有可能减少。然而，当杀虫剂也应用时，这种除草剂的间接效应就无法被检测到，这似乎是由于氟虫腈的高致死毒性所致。我们的研究强调了物种特征（如微生境利用）的重要性，这些特征可以用来预测农用化学品的间接影响。鉴于化学品的间接影响会因物种特征和其他化学品的直接毒性而变化，需要努力解释这种变化，以预测农用化学品间接影响的现实风险。
