TOXICITY OF CASTOR OIL, RICINUS COMMUNIS (LINN.)TO ANGOUMOIS GRAIN MOTH, SITOTROGA CEREALELLA (OLIVIER) INFESTATION IN PADDY RICE.

Abstract

Different oil extracts of Ricinus communis and solvents were evaluated for their insecticidal efficacy against the Angoumois grain moth, Sitotroga cerealella (Olivier) infestation in paddy rice in the laboratory at a temperature of 28±2oC and a relative humidity of 75±5%. The solvents used in extracting the oil are acetone, ethanol, n-hexane and petroleum ether. The oil extract at 0.005%w/v, 0.015%w/v, and 0.025%w/v was applied to 5ml/20g of paddy rice. Ten adult moth (day old) were introduced after 24hr of treatment. Parameters evaluated for moth were adult mortality, emergence, developmental period and susceptibility of adult; water absorption and viability of treated paddy rice after infestation. Results show that adult mortality increased as concentration of oil increased. The extract from the four solvents tested against S. cerealella were able to effect 100% mortality at all concentrations within 96hr of application. Significant differences (p<0.05) existed among the oils and the concentration. A 100%, 80%, 63% and 56% mortality rate was obtained within 24hr when ethanol, acetone, petroleum ether and n-hexane extract of R. communis respectively was applied at 0.025%w/v/20g of paddy rice. Adult emergence shows that more adult S. cerealella emerged from the control which was significantly higher than (p<0.05) than others. Fewer or no adults emerged from paddy treated with oil extract of R. communis when compared with ordinary solvent and control. Generally, adult emergence was low at all concentrations. At all concentrations, adult emergence was zero in oil extracts, except for n-hexane extract at 0.015%w/v and n-hexane and petroleum ether extracts at 0.05%w/v which had one. This shows that ethanol extract had the greatest insecticidal activity while the least effective was n-hexane extract. The treatment which achieved the highest mortality also had the least adult emergence. Water absorption and viability was not hampered by the treatment, although percentage viability in the controls was far higher than in treated seeds