蘇鐵白輪盾介殼蟲及銀葉粉蝨之真菌性天敵調查與其在生物防治潛能之評估

Abstract

蘇鐵白輪盾介殼蟲(Aulacaspis yasumatsui Takagi) ，於2001年在台灣北部被發現後，逐漸往南部傳播感染至一般庭院、校園之蘇鐵，此外甚至傳播至東部台東紅葉村之台東蘇鐵（Cycas tailungensis）自然保護區內。 蘇鐵白輪盾介殼蟲是台灣外來種，對於台灣特有種台東蘇鐵危害嚴重導致大量枯萎。台東自然保護區內地形崎嶇，施用化學藥劑困難、成本高，並且有污染水源之虞，因此尋求生物防治似為較佳之策略。另外，銀葉粉蝨 (Bemisia argentifolii) 和白輪盾介殼蟲皆為同翅目，是多年來為害洋香瓜及其他瓜類之重要害蟲，且是傳播多種植物病毒的媒介昆蟲，故本實驗也將其視為防治目標之一。蟲生真菌常被開發為真菌性殺蟲劑，施用於田間對環境影響小也可有效控制害蟲族群數量。自林間採集受白輪盾介殼蟲嚴重感染之蘇鐵葉片，剪枝後以濕室培養數日後分離蟲體上可能之蟲生真菌，以型態、分子特徵進行鑑定。除此之外，為蒐集足夠之生物防治候選菌株，亦針對粉蝨以及台灣各林地，進行採集以及分離可利用之蟲生真菌。自台灣各地共採集19種蟲生真菌，而其中在台東蘇鐵保護區內發現之Simplicillium lanosoniveum, Torrubiella luteorostrata, Fusarium coccophilum, Myriangium duriaei是首次被發現的白輪盾介殼蟲生物性天敵。對其中S. lanosoniveum, T. luteorostara, F. coccophilum以及Paecilomyces javanicus,進行生物防治潛能評估後發現，P. javanicus,在寄主範圍、生長速率、產孢能力表現皆優於其他三者。至於F. coccophilum ，其在各類培養基中生長緩慢，各菌株表現差異大，且病原性弱，評估後較不建議使用於生物防治。而酵素測定實驗顯示，S. lanosoniveum可產生最多的蛋白質分解酵素和脂質分解酵素。在白輪盾介殼蟲接種試驗當中，相對於對照組在六天後達到50%死亡率，四種蟲生真菌皆可使90%的介殼蟲死亡。而粉蝨族群在接種此四種蟲生真菌後十一天，和對照組相比，只有T. luteorostara 表現優於對照組，可以使50%的粉蝨族群死亡。另外，在小規模的產孢試驗中，蟲生真菌在以燕麥做為基質的培養基中產孢狀況最好，並以P. javanicus最為明顯。綜觀四種蟲生真菌之評估，P. javanicus做為白輪盾介殼蟲生物防治劑之潛力最大，未來可以藉由劑型研發以及最佳化接種方式、施用時機或配合其他防制措施，以提升其致病力和防治效力。

Cycad scale insect Aulacapsis yasumatsui was accidentally introduced into Taiwan since 2001 onward. The pest spread quickly islandwide and devastated more than 90% cycads in Taitung National Cycad Conservation Area (TNCCA). Concerning about the potential water resource contamination by the pesticides and also the rugged mountainous landscape, biocontrol by potential entomopathogenic fungi (EPF) is more feasible. Additionally, the silver leaf whitefly (Bemisia argentifolii) not only severely infested the cucumber and melon, but also transmitted severe mosaic plant viruses. Therefore, whitefly was also selected as the target pest for biocontrol target. The experiments were initiated starting from survey of the potential EPF candidates, pathogenicity and host range tests, small scale inoculum mass production, and finally appraisal of their efficacy in the control of CAS and whitefly under laboratory condition. Totally nineteen EPFs were isolated from different niches in Taiwan. Four major EPFs: Simplicillium lanosoniveum, Torrubiella luteorostrata, Fusarium coccophilum and Myriangium duriaei associated with CAS in TNCCA, and were firstly reported as the natural fungal enemies of CAS, and the epizootic caused by them also observed from 2008 to present. Furthermore, S. lanosoniveum, T. luteorostrata, F. coccophilum and Paecilomyces javanicus isolated from an infested caterpillar were evaluated for the biocontrol potential. P. javanicus showed the widest host range, rapid growth rate, and superior sporulation capacity as well. On the other hand, F. coccophilum exhibited slow growth and narrowest host range also distinct difference in virulence among strains. In the enzymes activity tests, S. lanosoniveum exhibited the highest protease and lipase activities. In the inoculation test of A. yasumatsui by the four EPF, more than 90% of scale larvae succumbed after six days, compared with the 50% mortality of the control. Regarding the whitefly, B. argentifolii, T. luteorostrata showed the higher pathogenicity, this resulted in 50% morality after 11 days. In small scale trial of inoculum mass production, the outcome indicated that oat was the best substrates for sporulation for these four species of EPF. Overall, P. javanicus possessed the highest potential and regarded as one of the best candidates developing as a biocontrol agent to control CAS, whiteflies or other devastating insect pests. Nevertheless refinement of the formulation, further enhancing pathogenicity and application techniques are needed.