CONTACT AND FUMIGANT EFFICACY OF POWDERED AND INTACT OCIMUM-CANUM SIMS (LAMIALES, LAMIACEAE) AGAINST ZABROTES-SUBFASCIATUS (BOHEMAN) ADULTS(COLEOPTERA, BRUCHIDAE)

The efficacy of powdered and intact dried leaves of Ocimum canum Sims were determined against adult Zabrotes subfasciatus (Boheman) in dried Pinto beans. The finely-powdered dried leaves suppressed oviposition completely at 2% w/w, with an EC50 of 0.45% w/w. None of the concentra tions of intact dried leaves caused a reduction in population, but, in creasing concentrations did cause a weak but significant increase in f ecundity. At 5% intact leaves (w/w) the number of eggs, hatched eggs a nd adult F1 progeny were 110, 110 and 111% of those for the control, r espectively. Additional experiments determined that 1% powdered leaves (w/w) in pinto beans caused 100% mortality of adult Z. subfasciatus i n 48h. An assessment of the fumigant toxicity of powdered O. canum lea ves indicated that 24 g/l had an LT50 of 8.15 h. Linalool is the major chemical present in extracts of O. canum leaves. Neat linalool, howev er, at the amount which is extractable from 24 g of powdered O. canum leaves (207 mg/l) had an LT50 of 26.0 h. Linalool sorbed onto oat prot einaceous microparticles at 0.85% w/w (the concentration in powdered O . canum leaves) at 1% w/w in beans caused only 24 +/- 10% and 56 +/- 7 % contact mortality of female and male adult Z. subfasciatus at 48 h, respectively. However, fumigation trials with this preparation at 24 g /l had an LT50 of 83 h, which is very similar to that for the powdered leaves. Thus, the fumigant toxicity of powdered O. canum leaves can b e explained by the gradual release of linalool from the powdered mater ial. The contact toxicity evidently involves other chemical constituen ts. In addition to linalool present at 8.6 +/- 0.9 mg/g (previously re ported), powdered leaves of this supply of O. canum also contained bet a-caryophyllene at 0.8 +/- 0.1 mg/g and alpha-bergamotene at 3.4 +/- 0 .4 mg/g dry weight. These three compounds represented 97.2 +/- 0.3% of the material extracted from these dried leaves and probably adequatel y account for both the fumigant and contact toxicity.