LABORATORY EVALUATION OF ETHANOLIC EXTRACTS OF GARLIC (Allium sativum) CLOVES AND Aloe vera LEAVES AS PROTECTANTS AGAINST THE MAIZE WEEVIL, Sitophilus zeamais
ABSTRACT
This study evaluated the efficacy of ethanolic extracts of Allium sativum (Woodwill) cloves, Aloe vera (Miller) leaves and their mixture against Sitophilus zeamais (Motschulsky) under laboratory conditions. Experiments were carried out to check the toxicity, adult mortality, oviposition inhibition, repellent and anti-feedant effects of these plant extracts against S. zeamais. The experiments were laid out in a completely randomized design of ten treatments replicated three times. The adult weevils were exposed to maize grains treated with three concentrations (200, 250 and 300mg/ml) 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 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. Most mortality occurred within 24hr of treatments showing that the extracts had no residual toxicity. Among the extracts used, the mixture recorded highest adult mortality (43.3%) followed by A. sativum (35%) and A. vera (30%). The plant extracts showed varying levels of repellency to the weevils with the highest repellency (66.7%) recorded by the mixture followed by A. sativum (44.4%) and A. vera (26.7%). The extracts were able to lowerr progeny production with the mixture having the highest percentage inhibition rate (61.5%) while the control recorded the lowest (19.1%). Percentage grains weight losses was significantly higher in the untreated check than in the treated grains and are recorded as follows: mixture (3.5 %), A. sativum (6.1%), A. vera (14.1%) and control (29.3%). 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 were in the order: mixture > A. sativum > A. vera. Results also proved that A. sativum was 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 (200 < 250< 300mg/ml). The results in the present 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 having oviposition inhibition and anti-feedant effects, thus resulting in better protection of maize grains from pest damage.