Toxicity of essential oils of Piper aduncum and Piper hispidinervum against Sitophilus zeamais

Essential oils of Piper aduncum L. and Piper hispidinervum C. DC. (Piperaceae) were tested against Sitophilus zeamais Motsch. Contact, fumigant toxicity and topical effect were tested. Probit analysis was employed in evaluating the LC50 and LD50 response. Linear regression analysis and superposition of the bars (means error standard) were used for comparison of means percentage mortality. S. zeamais was more susceptible to the contact toxicity of the P hispidinervum oil than P aduncum oil with LC50 values of 0.51 and 2.87 mL cm(-2) of the oil, respectively. The mortality rate was nearly 100% at P. hispidinervum oil concentrations of 20 and 30%. With respect to the fumigant action, the weevil was more susceptible to the P. aduncum oil than to P. hispidinervum. A significant difference between oils mortality was observed only at 0.1 and 1.0% concentrations. For topical effect, similar values of the LD50 were obtained for essential oils. However, the mortality was higher with P aduncum. Essential oils of the P aduncum and P hispidinervum possess insecticidal effect from S. zeamais, but the responses varied according to concentration of the oils and exposure methods.