Department of Zoology and Center for Ecology, Southern Illinois University, Carbondale, Illinois 62901, USA.
Ecol Appl. 2010 Oct;20(7):1949-60. doi: 10.1890/09-0598.1.
In the midwestern United States, maize detritus enters streams draining agricultural land. Genetically modified Bt maize is commonly planted along streams and can possibly affect benthic macroinvertebrates, specifically members of the order Trichoptera, which are closely related to target species of some Bt toxins and are important detritivores in streams. The significance of inputs of Bt maize to aquatic systems has only recently been recognized, and assessments of potential nontarget impacts on aquatic organisms are lacking. We conducted laboratory feeding trials and found that the leaf-shredding trichopteran, Lepidostoma liba, grew significantly slower when fed Bt maize compared to non-Bt maize, while other invertebrate taxa that we examined showed no negative effects. We also used field studies to assess the influence of Bt maize detritus on benthic macroinvertebrate abundance, diversity, biomass, and functional structure in situ in 12 streams adjacent to Bt maize or non-Bt maize fields. We found no significant differences in total abundance or biomass between Bt and non-Bt streams, and trichopterans comprised only a small percentage of invertebrate biomass at all sites (0-15%). Shannon diversity did not differ among Bt and non-Bt streams and was always low (H' range = 0.9-1.9). Highly tolerant taxa, such as oligochaetes and chironomids, were dominant in both Bt and non-Bt streams, and macroinvertebrate community composition was relatively constant across seasons. We used litterbags to examine macroinvertebrate colonization of Bt and non-Bt maize detritus and found no significant differences among litter or stream types. Our in situ findings did not support our laboratory results; this is likely because the streams we studied in this region are highly degraded and subject to multiple, persistent anthropogenic stressors (e.g., channelization, altered flow, nutrient and pesticide inputs). Invertebrate communities in these streams are a product of these degraded conditions, and thus the impact of a single stressor, such as Bt toxins, may not be readily discernable. Our results add to growing evidence that Bt toxins can have sublethal effects on nontarget aquatic taxa, but this evidence should be considered in the context of other anthropogenic impacts and alternative methods of pest control influencing streams draining agricultural regions.
在美国中西部，玉米残体进入农业土地排水的溪流。转基因 Bt 玉米通常种植在溪流沿岸，可能会影响底栖大型无脊椎动物，特别是毛翅目昆虫，它们与一些 Bt 毒素的靶标物种密切相关，是溪流中重要的碎屑食者。Bt 玉米对水生系统的输入的重要性最近才被认识到，而且缺乏对水生生物潜在非靶标影响的评估。我们进行了实验室喂养试验，发现与非 Bt 玉米相比，喂食 Bt 玉米会使叶片撕碎的毛翅目昆虫 Lepidostoma liba 的生长速度明显变慢，而我们研究的其他无脊椎动物类群则没有显示出负面影响。我们还使用现场研究来评估 Bt 玉米残体对 12 条毗邻 Bt 玉米或非 Bt 玉米田的溪流底栖大型无脊椎动物丰度、多样性、生物量和功能结构的影响。我们发现 Bt 和非 Bt 溪流之间的总丰度或生物量没有显著差异，并且在所有地点（0-15%）毛翅目昆虫仅占无脊椎动物生物量的一小部分。Bt 和非 Bt 溪流之间的 Shannon 多样性没有差异，而且始终很低（H'范围为 0.9-1.9）。高度耐受的类群，如寡毛类和摇蚊科，在 Bt 和非 Bt 溪流中都占主导地位，并且无脊椎动物群落组成在整个季节都相对稳定。我们使用凋落物袋来研究 Bt 和非 Bt 玉米残体的大型无脊椎动物定殖，发现凋落物或溪流类型之间没有显著差异。我们的现场发现与我们的实验室结果不一致；这可能是因为我们在该地区研究的溪流高度退化，受到多种持续的人为胁迫（例如，渠道化、改变水流、养分和农药输入）的影响。这些溪流中的无脊椎动物群落是这些退化条件的产物，因此，单一胁迫因素（如 Bt 毒素）的影响可能不易察觉。我们的结果增加了越来越多的证据，表明 Bt 毒素对非靶标水生类群可能具有亚致死效应，但应将这些证据置于其他人为影响和影响农业地区溪流的替代害虫控制方法的背景下考虑。
