Assessment of the insecticidal properties of some plant extracts as grain protectants against maize weevil. Sitophilus zeamais Motschulsky
ADEDIRE, C.O. and T.S. AJAYI
Acetone extracts of ten plant materials namely, Garcinia kola Heckel, Citrus frutescens L., C. sinensis Osbeck, C. parandis Nacfr., C. aurantifolia Swing, Afromomum melegueta Schum, Cymbopogon citratus L., Xylopia aethiopica Rich, Allium cepa L. and Piper guineense Schum and Thonn were evaluated for their
insecticidal activity against the maize weevil, Sitophilus zeamais Motch. The results indicated that C. frutescens, P. guineense and A. melegueta effectively protected maize grains against weevil attack. All the three plant extracts exhibited fumigant mode of
action since they each have a characteristic pungent smell. It appears P. guineense and C. frutescens acted mainly through the contact mode of action while A. melegueta needed to be absorbed through the cuticle or ingested before it can be effective. Only acetone-extracts of A. cepa, C. citratus and C. aurantifolia were
the least effective of the plant materials tested while others were moderately effective. Based on weevil perforation index (WPI) , the results of this investigation showed that all the plants tested had some insecticidal activity.