Evaluating the effectiveness of insecticides on storage bag surfaces for managing Callosobruchus maculatus (fabricius) (Coleoptera: Bruchidae)

Abstract

Incorporating insecticides into storage bags is emerging as an effective strategy for pest management. This study evaluated four insecticides (malathion 50 E.C., lambda-cyhalothrin 5 E.C., spinoteram 11.7 S.C., and azardirachtin 0.15% E.C.) for their contact toxicity against Callosobruchus maculatus adults. The insecticides were applied with LC₅₀ dosage to three different storage bag materials: jute, woven polypropylene (WPP), and 50% polypropylene-reinforced jute. Treatments were sprayed using a glass atomiser in three configurations: both sides treated, insect-exposed side treated, and non-exposed side treated. Twenty insects were exposed to the treated materials in closed Petri dishes, and immediate mortality was assessed at 1, 24, 48, and 72 h post-exposure. The bioassay revealed that all four insecticides achieved the desired mortality (>75%) in C. maculatus adults; spinoteram exhibited the highest mortality in the targeted insect; however, lambda-cyhalothrin was notably effective at a lower dosage (1.10 ppm) and shorter exposure time. The efficacy of the insecticides depended on the porosity of the storage bag material. Woven polypropylene bags treated on both sides exhibited the highest mortality (76–100%) among various treatment combinations. Miniature bags (21 × 16 cm) made of selected fabrics were treated with lambda-cyhalothrin (1.1 ppm) to assess their ability to contain C. maculatus infestation. The insects could not penetrate the WPP bag, while jute offered less resistance. The study suggests that applying all four insecticides at LC₅₀ dosages on various storage bag materials could be an effective management practice against C. maculatus adults. However, the application of lambda-cyhalothrin can achieve the desired results at lower concentrations.