Effect of Plant Powders on Survival, Oviposition and Progeny Development of Callosobruchus Maculatus for Protection of Leguminous Seeds during Post Harvest

Abstract

Insect infestation on leguminous plants particularly cowpea causes high destruction that lead to nutritional and economic losses. Hence powders from two medicinal plants namely Bersama abyssinica and Aristolochia elegans were tested for their efficacy as survival, oviposition and progeny development inhibitors of Callosobruchus maculatus to ensure food security. The experiments were conducted under laboratory temperature and relative humidity conditions and the powders were applied at rates 0.5g per 30g of cowpea seeds as contact toxicity to insects placed in Petri dishes. Results of contact toxicity assay showed that powders of Bersama abyssinica root bark and Aristolochia elegans seeds were effective against the adult C. maculatus by inducing 100% mortality within 5 days of application at the rate of 0.5g/30g of cowpea seeds. Few number of eggs approximately 1.50 ± 0.65 - 4.25 ± 0.65 per 50 seeds of cowpea seeds were oviposited and there was no progeny development of the cowpea weevil in seeds treated with plant powders. In untreated experiment the adult Callosobruchus maculatus survived and were able to lay eggs. The eggs were hatched and developed to F1 generation where 3.75 ± 0.25 approximately 45.8% adult C. maculatus emerged after 4 weeks .In the positive control, 100% mortality of C. maculatus occurred within 24 h and there was negligible seed loss in treated seed where as in untreated cowpea seed loss incurred by 37.00 ± 0.00 %. This study showed that all the tested plant powders were toxic to cowpea weevil thus could be applied by farmers by mixing with cowpea seeds to avert hatching of the eggs and development of larva, a destructive stage for management of insects and maintain nutritional and seed value in cowpeas.