Azadirachtin-Mediated Responses in the Maize Weevil, Sitophilus zeamais (Coleoptera: Curculionidae)

Corn is one of the world's most economically important cereal crops and can be attacked by Sitophilus zeamais. The control of S. zeamais is mostly based on synthetic insecticides; however, populations of this insect have developed resistance to various chemical compounds. New rational insecticides that prevent the development of resistant populations need to be continuously evaluated. This research aimed to assess the effects mediated by azadirachtin on S. zeamais populations in terms of mortality, survival, food preference, and repellency. Azadirachtin is toxic to S. zeamais at the larval (LC₅₀ = 3.36 ppm), pupal (LC₅₀ = 23.0 ppm), and adult (LC₅₀ = 37.7 ppm) stages. At all stages of insect development, the survival rate was 99.9% in insects not treated with azadirachtin, decreasing to 29.9%, 44.9%, and 68.5% in larvae, pupae, and adults treated with the LC₅₀ of the bioinsecticide, respectively. The preference for untreated corn grains was higher with the LC₂₅ and LC₅₀ of azadirachtin, while the LC₉₅ (209 ppm) repelled adults. Azadirachtin causes lethality in S. zeamais, compromising its survival and reducing the feeding preference on grains protected with repellent activity at high concentrations. Therefore, the use of this bioinsecticide may offer an alternative to control S. zeamais in the field and post-harvest.