病毒感染對入侵紅火蟻及臺灣本土螞蟻種間競爭之影響

Abstract

入侵紅火蟻撲滅計畫自2004年實行以來，有效地限制了入侵紅火蟻之擴散及其族群建立於重點防治區域。然而單蟻后族群婚飛造成之新發生點以及防治區域之再次入侵事件等，均持續發生。目前新的防治策略著重在整合性蟲害管理，結合餌劑及生物防治性天敵之防治方法。本研究目的為探討入侵紅火蟻體內新發現之單股RNA病毒 (Solenopsis invicta virus 1) 其作用在新生族群之入侵紅火蟻及兩種本土性螞蟻，熱烈大頭家蟻 (Pheidole fervens) 以及中華單家蟻 (Monomorium chinense) 種間競爭之影響，分別從個體與族群間干擾競爭能力探討。族群間干擾競爭之結果顯示，兩種本土性螞蟻在擁有數量優勢時，無論入侵紅火蟻感染病毒與否，的確有能力殲滅入侵紅火蟻之新生族群。中華單家蟻花費較少入侵時間去殲滅病毒感染之入侵紅火蟻相較於健康之火蟻。當入侵紅火蟻與相同數量之熱烈大頭家蟻競爭時，健康之入侵紅火蟻可完全殲滅熱烈大頭家蟻族群，但是經病毒感染之入侵紅火蟻，則需花費較長時間才能入侵成功。從試驗觀察結果，推測病毒感染造成入侵紅火蟻覓食行為及入侵能力之改變。遭受病毒感染之入侵紅火蟻與健康之入侵紅火蟻相比，派出之覓食工蟻較少，尤其在與其競爭之本土螞蟻出現的情況下。個體間干擾競爭之結果顯示出中華單家蟻造成病毒感染入侵紅火蟻小型工蟻較高之死亡率；然而入侵紅火蟻之大型工蟻憑藉著本身化學防禦及體型優勢，相對於本土性螞蟻表現高度競爭力。另外，熱烈大頭家蟻之兵蟻的確具備防禦功用，其造成入侵紅火蟻之高死亡率。由以上結果推測，遭受病毒感染或許造成入侵紅火蟻競爭能力之下降。中華單家蟻之化學防禦可能是造成遭病毒感染之入侵紅火蟻高死亡率之影響因子，但是熱烈大頭家蟻大顎攻擊之物理性防禦，並不會造成健康或病毒感染之入侵紅火蟻死亡率之差異。本研究突顯了整合競爭性及病原性防治天敵於火蟻區域性防治之可行性。

The fire ant (Solenopsis invicta) eradication program has been carried out in Taiwan since 2004. It certainly effectively restrains the populations of fire ant on treatment areas. Unfortunately, the reinfection or new infection site by natural nuptial flight of monogyne colony are still promulgated. Current new approaches to manage fire ants are integrating biological control agents with baits applications. This study aims to investigate alternative suitable biological control agents in Taiwan, and examines how SINV-1 (Solenopsis invicta virus-1) infection affects interspecific competition between incipient S. invicta against two native ants, Pheidole fervens and Monomorium chinense, by conducting two levels of trial, colony interference and individual confrontation, in laboratory conditions. The results from colony interference study showed that both native ants owing numerical advantages were capable to kill either infected or healthy queens of S. invicta. There was a significant less time for M. chinense to eliminate SINV-1 infected S. invicta compared to healthy ones. All S. invicta could repulse the invading of equal worker numbers of P. fervens. Compared with healthy S. invicta, SINV-1 infected S. invicta spent longer time to terminate P. fervens colonies. Virus infection was observed to have significant effects on foraging behavior and invading willingness of S. invicta. SINV-1 infected S. invicta recruited lesser number of foragers than healthy one, and in particular on competitive native ants were present. In confrontation trial M. chinense caused significant greater mortality on infected S. invicta minors than did on healthy ones. However, S. invicta majors (either infected or healthy) performed high competitive abilities against M. chinense, which might account for chemical defense and/or size advantages. In dealing with P. fervens, one cannot but admit that soldiers indeed function in defense, which caused S. invicta high mortality. These data suggest that virus may somehow weaken the competitive ability of infected S. invicta and make them prone to be terminated by M. chinense but not by P. fervens. Chemical interference by M. chinense might be a more likely influencing factor on mortality of infected S. invicta than the physical combat by P. fervens. Results from this study highlight the likely success on area-wide control of S. invicta in Taiwan by an alternative strategy that involves integration of competitors and pathogen.