Toxicity and repellency activities of the crude methanol extract of Duabanga grandiflora (Lythraceae) against Sitophilus oryzae (Coleoptera: Curculionidae).

Laboratory bioassays were carried out to examine the toxicity and repellency of a crude methanol extract of Duabanga grandiflora against adult rice weevil, Sitophilus oryzae. Toxicity was evaluated using a nochoice test with treated filter paper and rice grains while repellency evaluated using a choice test with treated filter paper. The crude methanol extract was found to possess low toxicity against S. oryzae with maximum mortality of 33% at 32 mg/mL (w/v) 7 days after exposure. Toxicity depended on both concentration and duration. The crude methanol extract was also repellent against S. oryzae ranging from 37 and 83% at 5 min to 2 h after exposure and from 60 to 100% at 4 to 24 h after exposure. The exposure period appeared to be the most important factor affecting the repellent effect of crude methanol extract of D. grandiflora (P 0.05).