蜜蜂幼蟲期餵食亞致死劑量益達胺對成蟲腦神經連結之影響

Abstract

殺蟲劑的使用是為了害蟲防治，然而，也會影響到作物的授粉者，如蜜蜂。益達胺是一種常見的系統性神經毒農藥，作用於菸鹼酸乙醯膽鹼接受器，造成昆蟲神經系統的過度興奮而死亡。過去研究顯示蜜蜂於幼蟲期暴露於亞致死劑量的益達胺會造成成蟲的嗅覺學習能力下降。在蜜蜂腦中的蕈狀體管理了多種訊號之整合，與學習、記憶、認知過程相關聯，其中的突觸單元隨日齡而增長，學習能力亦是。此突觸可塑性是蜜蜂面對環境各種任務所做的適應以及內部調節之基礎。本研究藉由免疫染色標定蕈狀體中杯狀構造的突觸單位來探討亞致死劑量的益達胺對蜜蜂神經發育的影響。結果發現蜜蜂於幼蟲期餵食亞致死劑量益達胺會造成杯狀構造中突觸單元密度的下降，證實了嗅覺學習能力的下降跟蕈狀體中異常的神經連結相關，也代表益達胺對蜜蜂的影響從幼蟲期即對神經系統發育造成損害。

Pests are the target of pesticides. However, pesticides affect pollinators simultaneously, such as honey bees. Imidacloprid, a common systemic pesticide, acts on the nicotinic acetylcholine receptors and causes hyperexcitation in the nervous system of insects. Previous study showed the decrease of honey bees’ learning ability after exposing to sublethal dosage of imidacloprid in the larval stage. The learning ability may be related to mushroom bodies, which is responsible for the multisensory integration and are associated with learning, memory and cognitive processing in the insect brain. In the mushroom bodies of honey bee worker, the synaptic connectivity increases with age, and so as the learning ability. This synaptic plasticity is the base for the honey bees to cope with different tasks in the environment and make internal adjustment. In this study, immunohistochemistry is used to label the synaptic units in the calyces of mushroom bodies to see the sublethal effects of imidacloprid on the neural development. The results indicate that the density of synaptic units in the calyces region decreases after feeding with sublethal dosages of imidacloprid. This links the decrease of olfactory learning ability to abnormal neural connectivity, and thus demonstrates the imidacloprid impairs the development of nervous system from the larval stage of honey bees.