Abstract

The maize weevil Sitophilus zeamais is a primary pest of stored grains, and it is primarily controlled through the use of synthetic insecticides, which are directly connected to increases in the resistance of these insects. In this study, populations of S. zeamais acquired from small farmers in southern Piauí were obtained, and an experiment was performed with the insecticide K-Obiol EC25, with dose-response concentrations ranging from 3.5 ´ 10^-4 to 0.05 g i.a/cm². Five replicates containing 20 insects were used. For the amylase, lipase and total protease assays, 20 adult insects from each population were used separately for each treatment. The experiments performed with K-Obiol for the insect populations from different locations showed different LC₅₀ values_. The highest LC₅₀ value was from Currais at 94.0 µg i.a/cm², and the lowest value was from Bom Jesus at 14.0 µg i.a/cm². The specific activities of the energy metabolism enzymes (lipase and amylase) responsible for sugar hydrolysis in four populations of S. zeamais exposed to the insecticide K-Obiol at different times (1, 6, 12 and 24 h) were determined. In all of the populations, the greatest amylase activity was observed in the group of insects exposed to the insecticides for 12 h. The population from Currais showed greater lipase activity in the treatment with 1 h of exposure to deltamethrin, whereas the population from Colônia showed the lowest lipase activity in the treatment with 24 h of exposure.

Key words: Deltamethrin, enzyme activities, amylase, lipase, protease.