Pathogenicity of entomopathogenic fungi, Metarhizium anisopliae against tobacco caterpillar, Spodoptera litura (Fabricius).

In developing effective replacements for toxic chemicals, entomopathogenic fungi have been considered as an alternative. The efficacy of entomogenous fungus Metarhizium anisopliae in controlling Spodoptera litura was studied by bioassay test. Larvae of 4–5, 10–11 and 15–16 days old were sprayed with six conidial concentrations ranging from 103 to 108 conidia ml−1. The median lethal concentrations (LC50) recorded with M. anisopliae isolate, MTCC 4101 were 4.44x104, 4.45x106 and 1.62x108 conidia ml−1 for 4–5, 10–11 and 15–16 days old larvae of S. litura respectively, while in case of MTCC 4103 isolate these were 1.95x105, 6.71x106 and 6.9x108 conidia ml−1 respectively. Relative LC50 between the isolates showed that LC50 values of MTCC 4103 isolate were 4.39, 1.50, 4.26 times more than MTCC 4101 for 4–5, 10–11 and 15–16 days old larvae, respectively. The LT50 values that were calculated at highest concentration of test fungi were 101.16, 116.51 and 149.75 h for 4–5, 10–11 and 15–16 days old larvae of S. litura in MTCC 4101 isolate, while 99.27, 119.53 and 201.03 h for MTCC 4103 isolate respectively. Relative LT50 values between isolates indicated that MTCC 4103 isolate took 1.03 and 1.34 h more time to kill test insect. The results of bioassay indicated that susceptibility decreased with increase in age of larvae in terms of both LC50 and LT50. MTCC 4101 was comparatively more virulent than MTCC 4103 with lower LC50 and LT50 values.