Monarch butterfly (Danaus plexippus) populations have declined over the last two decades, attributable in part to declines in its larval host plant, milkweed (Asclepias spp.), across its breeding range. Conservation efforts in the United States call for restoration of 1.3 billion milkweed stems into the Midwestern landscape. Reaching this goal will require habitat establishment in marginal croplands, where there is a high potential for exposure to agrochemicals. Corn and soybean crops may be treated with neonicotinoid insecticides systemically or through foliar applications to provide protection against insect pests. Here, we investigate whether ovipositing monarchs discriminate against milkweed plants exposed to the neonicotinoid insecticide imidacloprid, either systemically or through foliar application. In our first experiment, we placed gravid females in enclosures containing a choice of two cut stems for oviposition: one in 15 ml of a 0.5 mg/ml aqueous solution of imidacloprid and one in 15 ml water. In a second experiment, females were given a choice of milkweed plants whose leaves were treated with 30 µl of a 0.825 mg/ml imidacloprid-surfactant solution or plants treated with surfactant alone. To evaluate oviposition preference, we counted and removed eggs from all plants daily for 3 d. We also collected video data on a subset of butterflies to evaluate landing behavior. Results indicate that neither systemic nor foliar treatment with imidacloprid influenced oviposition behavior in female monarchs. The implications of these findings for monarch conservation practices will be informed by the results of ongoing egg and larval toxicity studies.

中文翻译：

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帝王蝶（鳞翅目：蛱蝶科）对吡虫啉处理乳草的产卵反应

帝王蝶 (Danaus plexippus) 的数量在过去二十年中有所下降，部分原因是其幼虫寄主植物乳草 (Asclepias spp.) 在其繁殖范围内的数量下降。美国的保护工作要求在中西部地区恢复 13 亿根乳草茎。实现这一目标将需要在边缘农田建立栖息地，那里极有可能接触农用化学品。玉米和大豆作物可以用新烟碱类杀虫剂进行系统处理或通过叶面施用来提供对害虫的保护。在这里，我们调查了产卵君主是否歧视暴露于新烟碱类杀虫剂吡虫啉的乳草植物，无论是全身性还是通过叶面施用。在我们的第一个实验中，我们将怀孕的雌性放置在包含两个用于产卵的切割茎中的选择：一个在 15 ml 的 0.5 mg/ml 吡虫啉水溶液中，一个在 15 ml 水中。在第二个实验中，雌性可以选择叶用 30 µl 0.825 mg/ml 吡虫啉-表面活性剂溶液处理的乳草植物或仅用表面活性剂处理的植物。为了评估产卵偏好，我们每天计数并从所有植物中取出鸡蛋，持续 3 天。我们还收集了蝴蝶子集的视频数据来评估着陆行为。结果表明，吡虫啉的全身或叶面处理均不影响雌性君主的产卵行为。这些发现对君主保护实践的影响将通过正在进行的卵和幼虫毒性研究的结果来了解。