Enhanced toxicity of diallyl disulfide and carvone nanoemulsions against a stored bean pest and their nontarget effects on its parasitoid and seed viability

Botanical essential oils and their volatile constituents are increasingly recognized as environmentally safer alternatives to synthetic insecticides for managing stored-product pests. The adzuki bean beetle, Callosobruchus chinensis , is a cosmopolitan pest that causes substantial postharvest losses in legumes. In this study, nanoemulsions (NEs) of diallyl disulfide (a garlic-derived organosulfur compound), (R)-carvone (a spearmint-derived monoterpenoid), and their binary mixtures (1:1 and 2:1) were formulated using ultrasonication. The nanoemulsions consisted of spherical droplets (54–62 nm) and moderately high zeta potentials (−9.6 to −16.9 mV). Among treatments, diallyl disulfide NE exhibited the highest fumigant toxicity to C. chinensis , with an LC 50 of 0.79 µL active compound/L air at 24 h. Nanoemulsification enhanced efficacy by 30.5% for diallyl disulfide and 8.19% for carvone. Binary mixtures showed additive toxicity. Male beetles were generally more susceptible than females, except at a low concentration of the 1:1 mixture. At the 24 h LC 50 estimated for the host beetle, diallyl disulfide NE and the 2:1 mixture were less toxic (