Insecticidal activities of some medicinal plants against Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae) on stored maize

Abstract

A study was carried out to evaluate the insecticidal activity of Zanthoxylum zanthoxyloides, Aristolochia ringens, Garcinia kola, Morinda lucida, Euphorbia hirta, Croton zambesicus, Colocasia esculenta, Ficus exasperata and Tetrapleura tetraptera on Sitophilus zeamais at ambient temperature of 28 ± 2 °C and 70 ± 5% relative humidity. The plants powder was applied at 5, 10 and 20% (wt/wt) of maize grain. Weevil mortality, adult emergence, percentage damage, percentage reduction and weevil perforation index were observed. The result obtained showed that only the powder of Z. zanthoxyloides and A. ringens effect mortality on the weevil as they both achieved more than 50% weevil mortality within 96 h of application. However, powder of Z. zanthoxyloides had the highest mortality effect on the weevil as it achieved 100% within 72 h at 5%(wt/wt) and its effect was significantly (p < 0.05) different from other powders. Also, powder of Z. zanthoxyloides, A. ringens and M. lucida showed a reduction capacity on the emergence of the adult weevil at 20%(wt/wt). Moreover, Z. zanthoxyloides prevented the emergence of the adult weevil even at 5%(wt/wt) but effect was not significantly different from A. ringens and M. lucida at 20%(wt/wt) as they both achieved 0% and 0.67% adult emergence. The powders also reduced the damage of the treated seeds. Z. zanthoxyloides prevented the damage of the seeds at 5, 10 and 20%(wt/wt) while A. ringens prevented the seed damage at 20%(wt/wt). However, effect of all the powders increased with increase in the powder concentration.