A laboratory study was carried out to assess the effects of seed treatment and fumigation of artificially infested cowpea with the volatile oil of air-dried leaves of Ageratum conyzoides L. (Asteraceae). The oil exerted acute toxicity on adults of the cowpea weevil, Callosobruchus maculatus F. upon fumigation. Maximal mortality of 95–97% was inflicted by 60 μl oil. Application of oil dressing on cowpea seed exhibited remarkable insecticidal activity-against the weevil. Significant oviposition deterrency and complete inhibition of emergence of adult insects (F1 offspring) from oil-treated beans were evident at doses of 2.5 μl to 10 μ1/9.5 g beans. No adverse physical effects on the beans were noticed at these doses. The major isolate of the essential oil, precocene I, was four times as active as the oil.
