Management of lesser grain borer, Rhyzopertha dominica through nano bioformulations in stored rice

Nanoencapsulation of botanical insecticides has emerged as a promising strategy to improve the efficacy and stability of plant-derived compounds in stored-product pest management. The present study aimed to develop and evaluate nano silica-encapsulated formulations of neem (Azadirachta indica A. Juss.) oil, acorus (Acorus calamus L.) oil and the chemical insecticide imidacloprid for the management of Rhyzopertha dominica, a major pest of stored rice. Laboratory bioassays were conducted using contact toxicity and diet incorporation methods, followed by storage studies to assess long-term protective efficacy. The nano formulations were evaluated at different concentrations and adult mortality was determined using corrected mortality analysis. In contact toxicity assays, LC₅₀ values were 0.16 % for nano neem and nano acorus oils and 0.02 % for nano imidacloprid, compared with 0.17 %, 0.17 % and 0.03 %, respectively, for their conventional formulations. In the diet incorporation method, LC₅₀ values for nano neem, nano acorus and nano imidacloprid were 0.25 %, 0.26 % and 0.10 %, respectively, whereas conventional formulations recorded higher LC₅₀ values of 0.35 %, 0.47 % and 0.35 %. Storage studies revealed that nano silica-based formulations effectively protected rice seeds from insect infestation for up to five months without seed damage or weight loss. Furthermore, treated seeds maintained high germination percentage and seedling vigour throughout the storage period. The findings demonstrate that nanoencapsulation enhances the insecticidal efficiency and persistence of botanical oils while maintaining seed quality, highlighting its potential as a sustainable approach for protecting stored grains.