In vitro synergy of entomopathogenic fungi and differential-chemistry insecticides against armyworm Spodoptera litura Fabricius (Lepidoptera: Noctuidae)

Armyworm Spodoptera litura (Lepidoptera: Noctuidae) is a voracious pest with a wide host plants range. Synthetic insecticides are employed widely to control this pest leading to many ecological consequences. This necessitates looking for some biorational approaches to control this pest such as entomopathogenic fungi (EPF) and differential-chemistry insecticides which have different mode of action than the conventional insecticides. This study evaluated the insecticides (chlorantraniliprole, emamectin benzoate and lufenuron) and EPF (Beauveria bassiana and Metarhizium anisopliae) against 3rd instar larvae of S. litura using diet-incorporation and immersion methods respectively, alone and in binary combinations of the most effective treatments. Among differential-chemistry insecticides, chlorantraniliprole exhibited maximum larval mortality (24–100%) with minimum LC50 and LT50 values, followed by lufenuron (0–100%), while emamectin benzoate showed minimum larval mortality (0–68%) recorded at 24–96 h intervals. Among EPF, M. anisopliae showed significantly higher entomopathogenicity and caused 20–53% larval mortality than B. bassiana (5–35%) in 3–10 days post-exposure. Moreover, the binary combinations of M. anisopliae and chlorantraniliprole exhibited synergistic effect on S. litura larvae. It is concluded that chlorantraniliprole and M. anisopliae are effective biorational options exhibiting compatibility with each other which can be employed together against S. litura infestations and it will also aid to mitigate the insecticide resistance. However, field evaluations of these differential-chemistry insecticides along with EPF strains against insect pests and their impact on natural enemies constitute future perspectives of the study.