The research was conducted to evaluate the toxicity and residual effects of the hill toon, Cedrela serrata Royle methanolic leaves extract and its fractions against 5th instar of the red flour beetle, Tribolium castaneum (Herbst). Insects were reared under controlled laboratory conditions at 30±2 °C, 60±10% RH and a 16:8 h (L:D). The toxicity result revealed that LD50 of methanolic extract (ME), n-butanol fraction (NBF), ethyl acetate fraction (EAF) and aqueous fraction (AQF) was 143, 18, 70 and 384 µl/cm2, respectively. The most toxic fraction was NBF as its doses 20, 51, 102, 153 and 204 µl/cm2 revealed 73, 79, 85, 93 and 99% mortality, respectively, against 5th instars of T. castaneum. The residual effect, during 1st day at the highest dose of ME, NBF and EAF showed 100% mortality while, AQF showed 32%. However, during 7th day, it was 10, 26, 11 and 0%, respectively, for the same dose of ME, NBF, EAF and AQF. It was concluded that C. serrata extracts and their fractions showed significant toxicity and residual effects against 5th instars of T. castaneum. It is suggested that further research on C. serrata should be conducted to find out its active biological component(s).
Keywords: Cedrela serrata, lethal dose, residual effects, toxicity, Tribolium castaneum.