低溫對台灣地區埃及斑蚊與白線斑蚊幼蟲存活的影響

Abstract

埃及斑蚊與白線斑蚊在台灣有不同的分布，前者侷限於台灣的南部，後者則是全省都有分布。往昔研究認為冬季的氣溫可能是影響分布的因子之一。本實驗有三個部分，第一部分為實驗室內的試驗，我將埃及斑蚊與白線斑蚊的一齡及四齡幼蟲在低溫下處理不同時間，並以處理時間和存活率之間的線性迴歸來估算50%致死時間 (LT50)。結果發現，在一齡幼蟲中，白線斑蚊在2.5，5 及10oC的處理後均比埃及斑蚊有較高的存活率。白線斑蚊一齡幼蟲在10oC的50%致死時間長達526 小時，是埃及斑蚊一齡幼蟲的五倍長。在四齡幼蟲中，埃及斑蚊在2.5 及5oC的處理後存活率比白線斑蚊稍高，而白線斑蚊則是在10oC的處理後有較高的存活率。第二部分將一齡幼蟲在5oC下作四個世代的篩選，結果顯示兩種蚊子的耐寒能力均有增加。第三部分為田間試驗，於2004 年十二月底至2005 年四月將埃及斑蚊與白線斑蚊的一齡幼蟲飼育於自然環境中直到全部羽化或死亡，結果發現在有寒流來襲的月分中，白線斑蚊有較高的存活率。根據本實驗的結果推測，北台灣冬季的溫度對於埃及斑蚊的分布是一個可能的影響因子。

Aedes aegypti and Ae. albopictus differ in their distribution in Taiwan. The former species is distributed only in the south of Taiwan while the latter is found island-wide. One of the possible explanations proposed is that low temperature in winter to prevent the colonization by Ae. aegypti. Hence, the impact of low temperatures on immatures of both species is studied here in the laboratory and field. In laboratory experiments, first and fourth instar larvae were exposed to low temperatures for various times. I estimated the lethal time that could kill 50% of populations (LT50) using linear regression. For the first instar larvae, Ae. albopictus was more tolerant than Ae. aegypti at temperatures of 2.5, 5 and 10oC. First instar larvae of Ae. albopictus showed remarkable tolerance at 10oC and the LT50 was estimated to be 526 hours, which is five times to that of Ae. aegypti. For fourth instars, Ae.aegypti had greater tolerance than Ae. albopictus at 2.5 and 5oC, but Ae. albopictus had a greater tolerance at 10oC. First instars were selected at 5oC over four generations. Both species showed more tolerance after selection. Aedes aegypti showed a greater mortality than Ae. albopictus during exposure to cold fronts but the opposite was true in the absence of a cold front. The lethal effect of cold fronts on Ae. aegypti was identified from their daily mortality. My studies suggest that winter temperature in the north part of Taiwan may have a significant effect on the distribution of Ae. aegypti in Taiwan.