Effect of five medicinal plant leaves on survival, oviposition and progeny development of cowpea bruchid, Callosobruchus maculatus (F.) infesting cowpea seeds in storage

Over 90% of the insect damage to cowpea seeds is caused by Callosobruchus maculatus. Although, many chemicals have proven their efficacy against C. maculatus, they adversely affect the natural environment. Death of non-targeted species which are natural enemies of other insect pests and development of resistance to chemicals is possible. Therefore, the current study was conducted to determine the effect of plant leaves of Murraya koenigii (“Karapincha”), Pandanus amaryllifolius (“Rampe”), Vitex negundo (“Nika”), Pavetta indica (“Pavatta”) and Croton aromaticus (“Wel keppetiya”) on adult mortality, oviposition, and progeny development of C. maculatus. Plant leaves were tested in both fresh form and powdered form. The plant leaves were mixed with cowpea seeds to have two concentrations followed by the introduction of 5 pairs of C. maculatus adults. The maximum adult mortality, minimum oviposition and the minimum progeny development were observed when the cowpea seeds were treated with C. aromaticus leaves. The mortality increased to 100% when the seeds were treated with the combination of C. aromaticus – P. amaryllifolius – V. negundo (WPN) plant leaf powders.  This study suggests that fresh plant leaves or plant leaf powder of C. aromaticus can be used against C. maculatus to protect cowpea seeds in storage.