The pathogenicity of Beauveria bassiana (Balsamo) Vuillemin towards bagworm, Metisa plana Wlk. second and fourth instars of Metisa plana Wlk. was confirmed. The larvae were sprayed with different concentrations of conidia suspension and exposed at a temperature of 28±1°C and a relative humidity of 65%-75% and 85%-100% (‘ambient’ and ‘humid’ respectively). The percentage mortality, lethal concentration (LC₅₀) and the leaf area damaged (LAD) were calculated. B. bassiana was capable of infecting both stages of M. plana. The percetage mortality increased with increasing concentration of coxidia suspension. The LC₅₀ of B. bassiana for second instar was 4.2 x 104 conidia/ml under humid, and 1.5 x 10⁶ conidia/ml under ambient moisture conditions. For fourth instar the LC₅₀ was 2.4 x 10⁶ conidia/ml under humid and 2.5 x 10⁷ conidia/ml under ambient moisture conditions. Second instar of Metisa plana Wlk. was thus more susceptible to the pathogen than fourth instar. Increased humidity enhanced the pathogenicity of B. bassiana and lowered the feeding activity of M. plana.

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