Entomopathogenic bacteria and fungi as eco-safe substitutes to chemical insecticides against leaf eating caterpillars of Spodoptera litura

Abstract

The present study was carried out in laboratory conditions (25 ± 10°C and 70% humidity) for studying the bioefficacy of entomopathogenic fungi and Bacillus thuringiensis against Spodoptera litura using the leaf dip method. The insecticidal attributes of three different commercial bioinsecticides (Bacillus thuringiensis 0.5% W.P., Beauveria bassiana 1.0% W.P., and Metarhizium anisopliae 1.0% W.P.) at different concentrations (0.5, 1.0, and 1.5%) were evaluated against the 3rd and 4th larval instars of S. litura. The analysis of variance results revealed that the highest concentration (1.5% concentration) of B. thuringiensis against the 3rd instar larvae of S. litura caused a maximum 80 ± 0.28% larval mortality, followed by B. bassiana and M. anisopliae, which caused 72 ± 0.21 and 64 ± 0.20% larval mortality after 120 h exposure. The calculated median lethal concentration in probit analysis demonstrated the lowest median lethal concentration of 1.22/10 larvae (95% fiducial limit 4.71–11.45) in the 3rd instar larvae after 72 h. Similarly, in 4th instar larvae of S. litura, the highest concentration (1.5% concentration) of B. thuringiensis caused maximum 76 ± 0.23% larval mortality, followed by B. bassiana and M. anisopliae, causing 70 ± 0.21% and 64 ± 0.20% larval mortality after 120 h. The calculated median lethal concentration in probit analysis demonstrated the lowest LC50 = 1.59/10 larvae (95% FL: 1.08–2.36) in the 4th instar larvae after 72 h. Based on these studies, it was revealed that B. thuringiensis and B. bassiana showed maximum efficacy against S. litura larvae. Although M. anisopliae also exhibits insecticidal properties, all of these bioinsecticides can be used to manage the population of S. litura. These bioinsecticides can be included in integrated pest management programs as they do not pose any toxic hazards to the environment.