Bioactivity of the essential oil extracted from Evodia rutaecarpa Hook f. et Thomas against the grain storage insects, Sitophilus zeamais Motsch and Tribolium castaneum (Herbst)

The toxic, repellent and feeding deterrent activities of the essential oil extracted from Evodia rutaecarpa Hook f. et Thomas, were evaluated against Sitophilus zeamais adults and Tribolium castaneum larvae and adults. Contac t toxicity assayed by topical application showed that S. zeamais adults wer e significantly more susceptible (LD50=0.043 mu g/mg body wt) to the essent ial oil than T. castaneum adults (LD50 = 0.118 mu g/mg body wt) and larvae (LD50 = 0.093-0.126 mu g/mg body wt). However, in the fumigation assays, S, zeamais (LC50 = 41 mu g/L air) was less susceptible to the essential oil t han T. castaneum (LC50 = 11.7 mu g/L air). When compared with larvae of var ious ages, T. castaneum adults were more susceptible to the fumigant toxici ty of the essential oil. Also, in the treated filter paper repellency test, the essential oil was more repellent to T. castaneum than to S. zeamais. A flour disk bioassay demonstrated that the essential oil of E. rutaecarpa h ad a weaker feeding deterrent action against T. castaneum adults than again st T. castaneum larvae and S, zeamais adults. The reduction in growth rate of T. castaneum larvae and S. zeamais adults was mainly due to a behavioura l (feeding deterrent) action rather than to post-ingestive toxicity of the oil. (C) 1999 Elsevier Science Ltd. All rights reserved.