Laboratory Evaluation of Selected Biorational Insecticidal Formulations against Potato Leafworm Spodoptera litura Fabricius (Lepidoptera: Noctuidae)

Spodoptera litura Fabricius (Lepidoptera: Noctuidae) is a deleterious agricultural pest worldwide. Field populations of S. litura manifest resistance to almost all conventional insecticides and it is imperative looking for novel biorational insecticides to control this pest. In this regard, this study bioassayed some promising biorational insecticides including botanical, microbial and non-conventional synthetic insecticidal formulations against 3rd instar larvae of S. litura. Bioassay with botanical formulations showed a significant toxicity of oil and extract formulations of neem (Azadirachta indica) causing 70-77% larval mortality in 72 h observation and exhibiting minimum medial lethal concentration (LC50) and time (LT50) values (i.e. 12.32 and 38.01 ppm and 16.67 and 11.68 days, respectively). Among microbial formulations tested, S. litura-nuclear polyhedrosis virus (NPV) and Bacillus thuringiensis kurstaki appeared as the most effective microbial treatments exhibiting minimum LC50 (3.78 x 103 OB mL-1 and 1.22 x 107 spores mL-1, respectively) and LT50 (3.83 and 3.71 days, respectively) values. While flubendiamide, chlorantraniliprole and spinetoram exerted most significant lethal and sublethal effects on S. litura with minimum LT50 values (i.e. 19.58, 30.78 and 26.25 h, respectively). Larval development time was significantly prolonged by both half and one-fourth doses of flubendiamide and chlorantraniliprole (19.51 and 19.63 days and 17.77 and 17.20 days, respectively), while pupal duration prolonged for spinetoram and lufenuron. Similarly, significant suppression of adult lifespan was exhibited by flubendiamide (11.83 and 11.85 days) and chlorfenapyr (12.28 and 12.06 days). Overall study results advocate further consideration of these aforesaid biorational insecticides against S. litura infestations. However, assessment of their compatibility with each other and with other IPM strategies both under lab and field conditions constitutes future perspectives of this work.