Abstract:
Maize weevil (Sitophilus zeamais, Motsch.) is a ubiquitous and cosmopolitan field-tostore
pest of maize of economic importance in tropical and subtropical regions of the
world. The current renewed interest to replace synthetic insecticides has served as the
impetus for the evaluation and intensification of eco-friendly anti-weevil measures such
as the use of plant based bio-insecticides. This study was therefore, designed to
investigate the insecticidal and repellent potency of leaf powders of Ruta graveolens and
Azadirachta indica in single treatments and combinations of various proportions under
ambient laboratory conditions against Sitophilus zeamais in both contact and vapour
forms. For both plants, 100 g each of maize grains were mixed with leaf powders at
different doses of 1.0, 3.0, 5.0, 7.0 and 10.0 g. The bio-potential of three combinations of
1:1, 1:2 and 2:1 of R. graveolens and A. indica leaf powders incorporating into the dosage
level of 10.0g was also evaluated. Maize grains treated with R. graveolens leaf powder
caused 100 % contact and 68 % fumigation mortalities within 24 hours of exposure
whilst repelling 97 % and 96 % weevils within an hour in both contact and vapour forms
respectively. A. indica powder was less efficacious compared to that of R. graveolens
causing significantly lower repellency within an hour and mortalities after 10 days of
storage. Application of 2:1 combination of R. graveolens and A. indica produced
respective levels of 100 % and 73% contact and fumigation mortalities within 24 hours
and highly significant repellent effects on S. zeamais, offering greater potential for largescale
storage since such combinations are relatively cheaper than using either of the
botanicals singly. Leaf powders of the two plants under present investigation revealed
their improved grain protecting capacity when used individually and in mixtures as biorational
leads in large-scale protection of stored maize.
