Abstract

The loss of stored grain is one of the most common problems faced by small farmers. The major pest of stored bean is the bean weevil (Zabrotes subfasciatus) as it can lead to total loss if left uncontrolled. The insecticide effect of 13 plant powders obtained from 11 different plant species was evaluated under laboratory conditions. The effect was assessed in terms of mortality, emergence of first-generation insects, percentage of damaged grain, ovicide effect, repellent, residual effect, and seed germination. A fully randomized experimental design with 52 treatments derived from a 13 × 4 factorial design (13 plant powders by four doses: 0.0, 0.1, 0.5 and 1.0%) was used. Results from residual effect and germination tests were analyzed with repeated-measures analyses. The highest percent of mortality was obtained with 0.1, 0.5 and 1.0% ofChrysactinia mexicana, and 0.5 and 1.0% of Gliricidia sepium powders. The lowest adult emergence was obtained with leaf powder of C. mexicana, G. sepium, Guazuma ulmifolia, Dyssodia pentachaeta, Dyssodia acerosa, Heterotheca inuloides and Zinnia acerosa, as well as with fruit powder of Crescentia alata and Melia azedarach. Setting 20% as the threshold for maximum grain damage, the C. mexicana leaf powder reduced damage when administered at 0.5 and 1.0%. C. mexicana, D. acerosa, D. pentachaeta, G. ulmifolia (fruit), H. inuloides, L. tridentata, D. stramonium and Z. acerosa powders had a significant repellent effect on Z. subfasciatus. The toxic effect of C. mexicana and G. sepium lasted 4 weeks. Grain germination was only reduced by G. sepium. Finally, 1.0% of C. mexicana led to the highest mortality of Z. subfasciatus eggs and the lowest percentage of damaged grain.

Key words: Plant insecticides, weevil, bean, Zabrotes subfasciatus, stored grain.