Abstract
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 Spodoptera litura 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 (Bacillus thuringiensis var. kurstaki), and entomopathogenic fungus (Beauveria bassiana and Metarhizium anisopliae) is assessed against the larvae of S. litura 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) > B. thuringiensis var. kurstaki (88.70 ± 1.01, 79.90 ± 2.01 and 78.00 ± 2.91) > B. bassiana (82.60 ± 2.46, 73.90 ± 2.46 and 73.00 ± 4.16) > M. anisopliae (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 B. thuringiensis @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 LC(50) 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 + B. thuringiensis < Barazide + B. bassiana < Barazide + M. anisopliae. 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 S. litura and at the same time farmers will decrease the inappropriate misuse and overuse of harmful chemical insecticides.