Insecticidal efficacy of Cleistopholis patens (Benth) against Sitotroga cerealella Olivier (Lepidoptera: Gelechiidae) infesting rice grains in Nigeria

Abstract

New sources of botanical pesticides in the management of Sitotroga cerealella (Olivier) infesting rice grains are indispensable in farmers' quest towards achieving maximum protection of their rice produce. In this study, the efficacy of root and stem bark of Cleistopholis patens as an insecticidal agent against S. cerealella was investigated at 28 ± 2 oC and 75 ± 6% relative humidity. Moths were exposed to contact and fumigant toxicity test at 0.5-2.5 g/20 g of paddy rice and mortality was assessed at 24, 48, 72 and 96 hours post-treatment respectively. Generally, moth exposed to root powders of C. patens showed higher mortality values (contact: 10 - 93%; fumigant: 13 - 100%) than their counterpart exposed to stem powder (contact: 6.67 - 78%; fumigant: 10 - 95%). Also, lethal doses (LD50 and LD95) revealed that lower doses of C. patens root powder resulted in higher mortality of S. cerealella when compared to that of stem powder. The only exception was observed in LD95 values of stem (6.54 g / 20 g of paddy rice) and root (6.76 g / 20 g of paddy rice) powder of fumigant toxicity test. Both powders of C. patens also significantly reduced adult emergence in treated grains when compared to control. This study showed that powders of stem and root bark of C. patens would provide a much desired wherewithal to synthetic insecticides in the management of S. cerealella infesting rice grains in Nigeria.