Bioactivity of eugenol, a major component of essential oil of Ocimum suave (Wild.) against four species of stored-product Coleoptera
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Toxicity and protectant potential of eugenol against Sitophilus granarius, Sitophilus zeamais, Tribolium castaneum and Prostephanus truncatus was investigated in the laboratory using contact toxicity, grain treatment and repellency assays. Eugenol applied topically, impregnated on filter papers, whole grains or glass pebbles was highly toxic to all the four species. Beetle mortality was dosage-dependent. Eugenol was more effective on grain than on filter paper discs since the lowest dosage of 1 mul/kg of grain killed all the beetles within 24 h. The effectiveness of eugenol was significantly reduced by the length of storage after application. For grains bioassayed after 10 days of storage following treatment mortality decresed to less than 30% even with the highest dose of 10mul/kg. Eugenol was also highly repellent to the four beetle species tested with overall repellency in the range of 80- 100%. Development of eggs and immature stages inside grain kernels was completely inhibited by eugenol treatment.