TOXICITY OF LEAF POWDERS OF MEXICAN TEA (Chenopodium ambrosioides L.) AND BOLDO (Peumus boldus MOL.) SINGLY AND MIXED WITH CALCIUM CARBONATE AGAINST MAIZE WEEVIL (Sitophilus zeamais MOTSCHULSKY)

Abstract

Stored grains are damaged by insect pests like maize weevil (Sitophilus zeamais Motschulsky; Coleoptera: Curculionidae). This study aimed to assess the biocidal properties of powdered foliage of Chenopodium ambrosioides L. and Peumus boldus Molina, both singly and mixed with calcium carbonate
at 0.5%, 1% and 2% (w/w), against Sitophilus zeamais Motschulsky under laboratory conditions. In 250 mL jars, 250 g of maize seeds were mixed with the treatments and then infested with 10 insect couples. Mortality and emergence of adult insects (F1), grain germination, fumigant and repellent effects of
powders were the evaluated parameters. The experimental design was completely randomized with 19 treatments, with five replicates. The whole methodology was repeated three times in different days. The highest mortality (100%) was obtained with plant powders alone at 2% (w/w) and the lowest adult insect emergence (0.2 y 0.1%) was reached with P. boldus powder alone at 1% and 2% (w/w). Seed germination was not affected by Ch. ambrosioides powder, while the use of P. boldus powder decreased germination respect to the untreated control. The fumigant effects of powders decreased as the proportion of calcium carbonate increased. Powders from both species mixed with calcium carbonate were repellent to S. zeamais. It was concluded that P. boldus powder and Ch. ambrosioides powder, singly and mixed with calcium carbonate, have insecticidal contact action, as well as fumigant and repellent effects on S. zeamais, and that they cause no significant effect on maize germination.