Efficacy of two plant powders as cowpea grain protectants against Callosobruchus maculatus Fabricius (Coleoptera, Chrysomelideae: Bruchinae)

Objective: This study was carried out to study insecticidal effect of powders from Chenopodium ambrosioides leaves and Aframomum melegueta seeds on cowpea weevil Callosobruchus maculatus.Methodology and Results: 5g of both powders of A. melegueta and C. ambrosioides were used in the proportions of C. ambrosioides 100%:A. melegueta 0%, C. ambrosioides 0%: A. melegueta 100%, C. ambrosioides 30%: A. melegueta 70%, C. ambrosioides 70%: A. melegueta 30% and C. ambrosioides 50%: A. melegueta 50%. Plant powders were added to 20g of cowpea grains. Bioassays were conducted at 26.64±0.74°C and 72.55±4.38% relative humidity. Insect mortality was evaluated from 24 to 144 hours after treatment. Results obtained indicated that plant powders had significant effect on C. maculatus mortality. The highest mortality rate (70.00±26.45%) was recorded in jar treated with C. ambrosioides.Conclusion and application of findings: Either plant powders, alone or mixed had high insecticidal effect on C. maculatus. Because of their effectiveness, these plant powders could be recommended as grain protectants against C. maculatus.Key words: Chenopodium ambrosioides, Aframomum melegueta, Callosobruchus maculatus, Insecticidal activit

Efficacy of mixed powders of Piper guineense and Zingiber officinale as maize grain protectants against Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)

This study was carried out to evaluate the effects of mixed powders of Piper guineense (Piperaceae) and Zingiber officinale (Zingiberaceae) on Sitophilus zeamais population and seed weight loss percentage of stored maize. Experiment was conducted under laboratory conditions (26.94 ± 0.81 °C, 74.76 ± 4.51% r.h. and 12 h photoperiod). In a completely randomized design with three replications, powders of P. guineense and Z. officinale were applied separately and in mixtures at the ratios of Zg100%:Pg0% (T1), Zg0%:Pg100% (T2), Zg30%:Pg70% (T3), Zg70%:Pg30% (T4) and Zg50%:Pg50% (T5), respectively. The mortality rate of S. zeamais adults was recorded and compared with the control at 24, 48, 72, 96, 120 and 168 hours after treatment. Maize grain damage and seed weight loss percentage were determined. Results showed highly significant differences with S. zeamais mortality rate between treatments, treatment exposure duration and their interactions (p<0.001). P. guineense, alone, showed the best efficacy (mortality rate = 96.66 ± 5.77% at 96 hours after treatment) and mixed with Z. officinale at the ratio 70%Pg: 30Zo (mortality rate = 93.33 ± 5.77%). Taking into account this high performance of P. guineense seed powder, it can be recommended as stored maize grain protectants.Keywords: Botanical insecticides, maize storage, Sitophilus zeamais, weight loss, mortality rate