Effect of oil-formulated Metarhizium anisopliae and Beauveria bassiana against the rice leaffolder Cnaphalocrocis medinalis Guenée (Lepidoptera: Pyralidae)

Abstract

The rice leaffolder (RLF), Cnaphalocrocis medinalis (Guenée) (Lepidoptera: Pyralidae), has become a major pest of rice in tropical Asia. The virulence of seven fungal isolates of Metarhizium anisopliae and Beauveria bassiana to third-instar C. medinalis was tested in initial screening bioassay by application of conidia at the concentration of 1 × 108 conidia/ml. Among the tested B. bassiana, MTCC7690 produced 83% mortality with shorter lethal time (LT50) of 4.64 days (4.51–4.76) and MTCC4104 of M. anisopliae produced 79% mortality with shorter lethal time (LT50) of 4.88 days (4.66–4.95). Further, the M. anisopliae MTCC 4104 and the B. bassiana MTCC7690 were formulated in the canola oil and were tested against the C. medinalis larvae at different concentration (1 × 103–1 × 108 conidia/ml). The mortality of the larvae was dose-dependent and the oil-formulated B. bassiana MTCC7690 conidia was highly virulent isolate with lower LC50 of 9.09 × 104 conidia/ml followed by oil-formulated M. anisopliae MTCC4104 conidia with LC50 of 6.08 × 105 conidia/ml. The oil-formulated effective isolates were tested with second to fourth larval instar and significant differences in mortality among the larval stages were obtained. Also, difference significant in lethal time with shorter lethal time was recorded in second instar larva. The effective canola oil-formulated isolates are known to significantly reduce the longevity of male and female than untreated controls. The significant reduction in the number of eggs laid by the fungi-treated female than untreated control was recorded.