Comparative fumigant toxicity of neem oil (Azadirachta indica A. Juss.) and pirimiphos-methyl on adults of Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae): lethal concentrations, lethal times, and transgenerational sublethal effects
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The maize weevil Sitophilus zeamais Motschulsky is one of the most destructive primary pests of stored cereal grains globally. Growing resistance to synthetic insecticides underscores the need for validated alternative tools. This study quantitatively compared the fumigant toxicity of neem oil ( Azadirachta indica A. Juss., NEEM AZAL 1,2% EC) and pirimiphos-methyl (ACTELLIC 50 EC) against adult S. zeamais . LC 50 = 0,72 mL/L for neem oil (R² = 0,85; slope = 2,56) and LC 50 = 6,31 mg/L for pirimiphos-methyl (R² = 0,92; slope = 2,47). Median lethal times (LT 50 ) ranged from 12-108 h (neem oil) and 12-44 h (pirimiphos-methyl). F1 progeny inhibition was 77,75-100% for neem oil and 62,93-100% for pirimiphos-methyl. Even at the lowest neem oil concentration (0,24 mL/L), progeny inhibition exceeded 75%, demonstrating azadirachtin's efficacy as an insect growth regulator. These results validate neem oil as an effective, low-resistance-risk, and environmentally sound replacement for pirimiphos-methyl within IPM schemes for stored-grain systems.
