Evaluation of botanical powders and extracts from Nigerian plants as protectants of maize grains against maize weevil, Sitophilus zeamais (Motschulsky) [Coleoptera: Curculionidae]

Toxicities of leaf powders and extracts of Acanthus montanus, Acanthospermum hispidum, Alchornea laxiflora and Argyreia nervosa against maize weevil (Sitophilus zeamais) were evaluated. Powders were tested at dose 3.0g/20g while extracts were tested at concentration 3%/20g of maize grains. Mortality, oviposition, and adult emergence rates as well as weight loss, seeds damage and weevil perforation index (WPI) were evaluated. Phytochemical constituents of the experimental plants were also carried out. The results showed that Acanthus montanus powder was the most potent with 65% adult mortality after 24 h of treatment. This is followed by Argyreia nervosa powder that evoked 52.5% weevil mortality. The least toxic to S. zeamais was Acanthospermum hispidum powder with 32.5% adult mortality. Extracts were more toxic than the powders of the tested plants. Acanthus montanus extract was the most toxic since it promoted 80% adult mortality after 24 h of treatment. Acanthus montanus, Alchornea laxiflora and Argyreia nervosa leaf powders and extracts completely prevented oviposition by adult insect, adult emergence, weight loss and seeds damaged. The phytochemicals present in Acanthus montanus were alkaloids (3.67 mg/g), saponin (3.33 mg/g), tannin (3.00 mg/g) and flavonoid (2.67 mg/g) contents. Acanthospermum hispidum had the least alkaloid (2.67 mg/g), saponin (1.67 mg/g), tannin (1.33 mg/g) and flavonoid (1.00 mg/g) contents. Acanthus montanus, Argyreia nervosa, Alchornea laxiflora and Acanthospermum hispidum were efficacious against S. zeamais instead of synthetic chemical insecticides that have environmental health hazards and they can be used in integrated pest management by farmers and foods merchants.

Keywords: Acanthospermum hispidum; Acanthus montanus; Alchornea laxiflora.; Argyreia nervosa; Insecticidal activity; Sitophilus zeamais.