Bio-control potential of Bacillus thuringiensis (Bacillales: Bacillaceae) and Metarhizium anisopliae (Hypocreales: Clavicipitaceae) against Chilo partellus Swinhoe (Lepidoptera: Pyralidae)

Abstract

The efficacy of most synthetic insecticides has been compromised against Chilo partellus (Swinhoe) due to its cryptic feeding behavior, hence there is a dire need to find other eco-friendly effective management approaches to combat this notorious pest. The susceptibility of 2nd and 4th larval instars of C. partellus was assessed against Bacillus thuringiensis var. kurstaki (Bt-k) (Berliner) and Metarhizium anisopliae (Mechnikov) under controlled conditions. The larvae were treated with individual or combined treatments of a single dose rate of B. thuringiensis (Bt: 0.75 µg/g) and three conidial concentrations (1x104, 1x106 and 1x108 conidia/ml) of M. anisopliae. The individual and combined application of both entomopathogens significantly affected the mortality, pupation, adult emergence, mycosis and sporulation of both larval instars of C. partellus. Maximum larval mortality (2nd instar: 94.63% and 4th instar: 91.43%) was recorded in combined applications of M. anisopliae (1x108 conidia/ml) and B. thuringiensis (0.75 µg/g). The same integrated treatment also caused significant declines in pupation (2nd: 0.00% and 4th: 6.66%) and adult emergence (2nd: 0.00% and 4th: 0.00%) of C. partellus as compared to rest of the experimental treatments. Moreover, a significantly higher rate of mycosis and sporulation were recorded in both larval instars (2nd: 88.52% and 143.96 conidia/ml) and (4th: 82.04% and 131.85 conidia/ml), when exposed to lower individual concentration of M. anisopliae (1×104 conidia/ml). The current results suggest that integrated application of M. anisopliae and B. thuringiensis could be a sustainable management tool for C. partellus in maize crop.