Abstract Entomopathogenic fungi Metarhizium anisopliae and Beauveria bassiana were isolated from soils and white grubs cadavers from farmlands in Nepal. In the mortality studies, 8 isolates infected more than 80% of the grubs, another 65 isolates infected more than 50% of the grubs and the rest of the isolates had a low level of pathogenicity with 107 conidia/mL concentration. Five isolates were highly pathogenic against third instar larvae of Maladera affinis. The isolate, M. anisopliae M1 was the most virulent strain of all the evaluated isolates. LT50 of the tested isolates varied between 2-9 weeks. Isolates M1 and M6 had the highest mortality rates and required the shortest time to kill the white grub larvae. Assessment with fungus inocula with conidiospores and blastospores against three different instars of white grubs showed that a significantly larger numbers of second instar larvae were infected with the fungi than first and third instars. A comparison of indigenous and commercial isolates of M. anisopliae and B. bassiana with third instar larvae of Anomala dimidiata, Adoretus lasiopygus and Phyllognathus dionysius demonstrated that native isolates were more virulent to the above three white grubs species tested than the exotic fungi. Based on this study, the indigenous virulent isolates have the potential to be biocontrol agents against white grubs in Nepal.
摘要 在尼泊爾，從田間土壤和蠐螬屍體中分離出的蟲生真菌：Metarhizium anisopliae (黑殭菌) 與Beauveria bassiana (本土白殭菌)。於致死試驗中，有8個分離株感染了超過80%的蠐螬，另有65個分離株感染了超過50%的蠐螬，而其餘濃度為107 conidia/mL的分離株致病力低。有5個分離株對Maladera affinis的3齡幼蟲有高度致病力。分離株M. anisopliae M1是所有分離株中檢測出毒性最強的品系。菌株的LT50測試結果介於2到9週之間。分離株M1與M6有最高的致死率，殺死白蠐螬的時間也最短。以真菌分生孢子與芽生孢子為接種原對抗3種不同齡期白蠐螬進行評估，顯示出2齡幼蟲遠較1齡與3齡幼蟲更容易被感染。比較本土與商品化的分離株M. anisopliae與B. bassiana對Anomala dimidiata、Adoretus lasiopygus與Phyllognathus Dionysius等3種白蠐螬3齡幼蟲的毒性，證明本土分離株高於外來真菌。根據此研究，尼泊爾原生的毒性分離株有成為對抗當地白蠐螬的生物防治劑之潛力。
| Key words: Beauveria bassiana, Metarhizium anisopliae, biological control, white grubs | | 關鍵詞: 本土白殭菌、黑殭菌、生物防治、白蠐螬。 |
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