ABSTACT
This study investigated the efficacy of ethanolic extracts of Allium sativum (Woodwill) cloves, Aloe vera (Miller) leaves and their mixture against Sitophiluszeamais (Motschulsky) under laboratory conditions. Parameters assessed were toxicity, adult mortality, repellency ,oviposition inhibition and anti-feedant effects of these plant extracts on S. zeamais.
The experiments were laid out in a completely randomized design of four treatments replicated three times. The adult weevils were exposed to maize grains treated with three concentrations (0.25, 0.30 and 0.35 g) of A. sativum and A. vera and equal proportion (50:50) of their mixture, while the control was treated with only the solvent.
Probit analysis revealed that A. sativum had lower LC50 than A. vera and therefore was more toxic than it. All treatments recorded higher significant (p<0.05) mortality than the experimental control. There was increase in adult mortality with days of exposure in all concentrations. Among the extracts used, the mixture recorded highest adult mortality (67.8%) followed by A. sativum(48.7%) and A. vera (24.5%). The plant extracts showed varying levels of repellency to the weevils with the highest repellency (76%) recorded by the mixture followed by A. sativum (60%) and A. vera (46%). The combination of both plants extracts ( synergistic effect) gave the lowest value of grain damage (4.55%) followed by A. sativum (7.14%), A. vera (15.46%) and control (42.06%). The overall results show that the mixture of the two plant extracts performed better in all bioassays than individual plant extracts. The efficacy of the treatments was in the order: mixture of A. sativum & A. vera (1:1) >A. sativum>A. vera. Results also showed that A. sativumwas a better biopesticide than A. vera. The effectiveness of the extracts was dose-dependent with the severity of their effects increasing with increase in concentration (0.25 < 0.30< 0.35g). The results in this study shows that the ethanolic extract of A. sativum cloves, Aloe vera leaves and their mixture are toxic to S. zeamais and can suppress progeny development of the weevils by inhibiting oviposition and feeding, thus resulting in better protection of maize grains from pest damage.
