Peel and leaf powders of three fruits and a vegetable as promising botanicals against Callosobruchus maculatus (F.)

The aim of this study was to examine the insecticidal activities of powders of bitter leaf, cashew leaf, orange peel and pawpaw leaf against Callosobruchus maculatus (F.) (Coleoptera: Bruchidae). These were tested at 2.5%, 5.0% and 7.5% (w/w) for their insecticidal activities against the insect. Results showed that the ovicidal and adulticidal activities of the plant powders depended on dosages and exposure time. Mortalities of 16.28% and 18.75% were observed in bitter leaf powder applied at 7.5% (w/w) dosage within 24 and 48 hours post infestation (HPI), respectively. In grains treated with 7.5% orange peel powder, 12.50% and 16.28% mortalities were observed within 24 and 48 HPI, respectively. Each of bitter leaf and orange peel powders was significantly different (p<0.05) in causing adult mortality at the highest dosage compared with the control. Oviposition was inhibited at the highest dosage of the plant powders, but the percentage of oviposition in the lower dosages was three-fold lower than the control. The plant powders also significantly reduced progeny emergence and grain damaged by the beetle. No beetle emergence was recorded in grains treated with bitter leaf powder at 27 DPI. Adult beetles in grains treated with cashew and pawpaw leaf powders caused grain damage of 46.3-54.7% and 44.7-60.7%, respectively during the study period. There was a noteworthy decrease in insecticidal effects of the plant powders as indicated: bitter leaf > orange peel > cashew leaf > pawpaw leaf. It is recommended that incorporating these plant parts in pest management of stored products will guarantee user safety, reduce environmental pollution and suppress insect infestation