Insecticidal efficacy of some plant powders and extracts against the Angoumois grain moth, Sitotroga cerealella (Olivier) (Lepidoptera: Gelechiidae)

Abstract

Powder and extract from four plants were evaluated for their insecticidal efficacy against the Angoumois grain moth, Sitotroga cerealella (Olivier) in the laboratory at a temperature of 28 ± 2°C and a relative humidity of 75 ± 5%. The plants included Aristolochia ringens L., Khaya ivorensis (K.), Strophanthus hispidus (D.C.) and Zanthoxylum zanthoxyloides Lam. The powder was applied at the rate of 0.2, 0.4 and 0.6 g/20 g of paddy rice, while the extract was applied at the rate of 1%, 2% and 3%/20 g of paddy rice. Parameters evaluated were adult moth mortality, adult emergence and weight loss in treated paddy after infestation. Results shows that adult moth mortality increased as concentration of powder increased. Significant differences (p < 0.05) existed among the plant powders andthe concentration. A 100% mortality rate was obtained within 7 days when A. ringens was applied at 0.4 and 0.6 g/20 g of paddy. S. hispidus was able to effect 100% mortality only at 0.6 g. This shows that A. ringens had the greatest insecticidal activity while the least effective was K. ivorensis. Adult emergence shows that more adult S. cerealella emerged from the control (40.3) which was significantly higher (p < 0.05) than others. Fewer adults emerged from paddy treated with plant powder with the least in A. ringens. Generally, adult emergence reduced with an increase in the concentration of powder. The extract from all the four plants tested against S. cerealella was able to effect 100% mortality of the adult moths within 24 h of application at all concentrations. Significant differences (p < 0.05) existed among all the different plant powders in terms of weight loss. The weight loss in paddy was significantly higher (p < 0.05) in the control (57.7%) than others. Weight loss was least in paddy treated with A. ringens at 0.4g/20 g of paddy with 2.2%. Generally, weight loss decreased with increase in powder concentration. The treatment with the highest adult emergence (control) also had the highest weight loss, while the treatment with the lowest adult emergence (A. ringens) had the lowest weight loss.