Insecticidal potential of Bacillus thuringiensis, Beauveria bassiana and Metarhizium anisopliae individually and their synergistic effect with barazide against Spodoptera litura

Excessive use of insecticides are responsible to contaminate the environment, soil health, developing resistance in the insect pests, introduces new species, toxic to human and eliminates non-target organisms and affects the eco-balance and biodiversity adversely. Application of microbial bio-agents with the chemical insecticides is an assertive way to manage the population of pests, in an addition to dropping down the chemical residues risk to the eco-system. Larval stages of <i>Spodoptera litura</i> are prolific eater, caused huge losses globally. Individual and combined effect of chemical insecticides Barazide (Novaluron 5.25 %+Emamectin benzoate 0.9 % SC), entomopathogenic bacterial (<i>Bacillus thuringiensis</i> var. <i>kurstaki</i>), and entomopathogenic fungus (<i>Beauveria bassiana</i> and <i>Metarhizium anisopliae</i>) is assessed against the larvae of <i>S. litura</i> in bio-assay experiment. The decreasing trend in the observed mortality among insecticides alone is Barazide (95.80 ± 1.16, 85.30 ± 1.85 and 82.00 ± 1.72) > <i>B. thuringiensis</i> var. <i>kurstaki</i> (88.70 ± 1.01, 79.90 ± 2.01 and 78.00 ± 2.91) > <i>B. bassiana</i> (82.60 ± 2.46, 73.90 ± 2.46 and 73.00 ± 4.16) > <i>M. anisopliae</i> (78.60 ± 1.46, 68.90 ± 2.96 and 69.00 ± 3.46) after 96 h at its highest inoculation level against 3rd, 4th and 5th instar larvae. The combined application of Barazide @0.1 % with <i>B. thuringiensis</i> @1.5%induced mortality cent percent after 72 and 96 h against 3rd and 4th instar. Chi-squared test indicated a significant level of mortality at p < 0.05 level at highest dose and the probit analysis showed lowest LC₅₀ value at dose 5.15 and 7.63 % with 95 % FL:1.38-19.22 and 2.85-20.39 after 72 and 96 h of exposure against 3rd and 4th instar. The increasing trend in the observed mortality among insecticides used in combination is Barazide + <i>B. thuringiensis</i> < Barazide + <i>B. bassiana</i> < Barazide + <i>M. anisopliae</i>. Insecticides used in combination induced synergism that providing valuable practice to manage insect pests. These results suggested that the combined treatments could be a successful method for controlling the population of <i>S. litura</i> and at the same time farmers will decrease the inappropriate misuse and overuse of harmful chemical insecticides.