亞澳地區入侵紅火蟻之病原感染型式與其潛在影響

Abstract

本研究針對亞澳地區內之入侵紅火蟻 (Solenopsis invicta Buren) 族群，進行各種常見病原之篩檢，包括了微孢子蟲Kneallhazia solenopsae，一種共生菌 Wolbachia sp.和兩種病毒 SINV-1/1A、SINV-2，除藉此探討這些地區的成功入侵是否符合脫離天敵假說 (enemy release hypothesis)，亦欲建立相關基礎資料，可供日後整合防治策略擬定時參考。經由 PCR、RT-PCR和鏡檢等技術檢測後，發現於台灣、中國、香港及澳洲所採集的火蟻樣本中，完全沒有K. solenopsae 和 Wolbachia的感染。此結果與脫離天敵假說相符，或可解釋為火蟻成功入侵該地區的原因之一。相較之下，SINV則頻繁出現於澳洲外其他被入侵地，其中 SINV-1/1A 的感染率為 48.4 %-55.6 %，且 SINV-1 僅出現於香港地區；而 SINV-2 則只出現於台灣樣本中，感染率達 16 %。由 SINV-2 之低感染率可推測，此病毒對於寄主適存值可能造成程度上的衝擊；而SINV-1/1A 於新入侵地火蟻族群內之感染情形則暗示，此病毒似乎對於寄主生存無顯著影響，故遭受感染之火蟻奠基族群能於新入侵地中各種選汰壓力下存活。經進一步藥劑試驗後，顯示受 SINV-2 感染之蟻巢對賜諾殺胃毒劑具有明顯較高之感受性；但在以因得克測試時，SINV-2、SINV-1A 感染與無感染蟻巢間，感受性則似無明顯差異。故欲了解 SINV 對寄主影響，仍需進一步的後續研究。本研究乃第一篇調查美洲地區以外入侵紅火蟻族群之常見病原的報告，並嘗試以脫離天敵假說解釋火蟻之成功入侵，亦為未來台灣火蟻的生物防治，提供了新的觀點。

The present study aims to survey the previously reported pathogens of Solenopsis invicta in Asian-Australian areas, such as Kneallhazia solenopsae, Wolbachia sp. and two species of viruses. With this research, it could not only test the enemy release hypothesis (ERH) to the successful invasions in Asian-Australian areas, but also build the basic data to help to formulate the strategy of integrate management in the future. By using specific PCR, RT-PCR and microscopic checking, no infections of K. solenopsae and Wolbachia sp. was found in populations sampled from Taiwan, China, Hong Kong and Australia. The pattern seems consistent with the ERH and may explain the successful establishment of S. invicta in these regions. In contrast, surprisingly, SINVs possess relatively higher prevalence and found in most of sampled populations. The infection rates of SINV-1/1A in different regions range from 48.4 to 55.6%, with only nests from Hong Kong found infected by SINV-1. The SINV-2 has only discovered in Taiwan with 16% infection rate. Lower prevalence of SINV-2 may provide a provisional hypothesis that the susceptibility to environmental stress of SINV-2-infected nests is relatively stronger. Accordingly, further hypothesis regarding negligible effect of SINV-1/1A on the establishment of propagule of fire ant could be considered. This hypothesis is subsequently supported by normal performance of infected nests in newly-infested spots that resulted from human transportation. The insecticide test showed that SINV-2 infected colonies were more sensitive to spinosad (by feeding) than either SINV-1A infected- or the healthy ones. In contrast, neither SINV-1A- nor SINV-2 infected colonies showed more susceptible to indoxacarb (by feeding) than healthy ones. More tests associated with fitness effect of virus infection on its host should be performed to address this issue. This is the first study to comprehensively survey the prevalence of known fire ant pathogens in recently non-American invaded areas which reinforces the role ERH involved in successful invasion of S. invicta, as well as provides a new perspective of biocontrol in Taiwan.