Abstract

Cowpea seeds are legumes particularly for consumptions by populations in tropical and sub-Saharan Africa. Effectiveness of powders of ginger (Zingiber officinale), alligator pepper (Aframomum melegueta), and pepper fruit (Dennettia tripetala) in single and mixed forms were evaluated for the control of cowpea weevils (Callosobruchus maculatus) under laboratory conditions. Toxicity bioassay adopted contact method at concentrations of 0.00, 0.05, 0.10, and 0.20% corresponding to 0.00, 1.25, 2.5 and 5.0 grams/25 grams of cowpea seeds in tripled replicates. Ten adult weevils were assigned to plant powders in petri dishes and adult mortality recorded after 30 days treatment exposures and seed viability was assessed. The results demonstrated that increased concentration of plant powders from 0.05-0.20% caused significant mortality of adult weevil (p<0.05). Highest mean mortality was achieved in 0.2% of mixtures of alligator pepper plus pepper fruit and pepper fruit plus ginger (mean= 2.00) with LC50= 3.31 and 3.39 g/25g cowpea seeds respectively. The number of seeds with damages, mean numbers of eggs deposited and weight loss across concentrations was 0.00 to 9.17 gram percent, 2.51, and 1.78%, respectively. Powders of D. tripetala in 0.1 and 0.2% concentrations also caused notable mortalities. The mixed forms recorded no eggs, seed damages and weight loss (mean= 0.00). Seed viability showed 50-100% germination and differences were not significant (p>0.05). Overall, this present study indicated that higher concentrations of plant powders in mixed forms could significantly reduce infestation of cowpea seeds.