Effects of Cleistopholis patens (Benth) extracts on cowpea seed beetle, Callosobruchus maculatus (Fab.) (Coleoptera: Chrysomelidae) infesting cowpea seeds in storage

Abstract

Cowpea seed beelte, Callosobruchus maculatus Fabricius (Coleoptera: Chrysomelidae) is a key pest of stored cowpea in the tropics. The seed is highly susceptible to the attacks of this beetle mainly between the period of harvest, processing and storage. The beetle is known to cause qualitative and quantitative losses which are manifested by seed perforations, reduction in weight, reduction in seed germination and all these have resulted into farmers’ low income from the crop. This work is therefore designed to evaluate the use of the extracts of the leaf, stem bark and root bark of Cleistopholis patens (Benth) on Callosobruchus maculatus (Fab.) for mortality, oviposition and adult emergence effects. The extracts of the plant parts were obtained using n-hexane solvent in the Soxhlet apparatus. The extracts of the plant parts were tested at 1, 2, 3, 4 and 5% v/g treatment levels respectively. Control experiments were also set up. Adult mortality and repellent test were monitored daily for 96 h while result of ovicidal test was recorded at 35 days after treatment. All the three extracts applied were able to cause significant (P < 0.05) adult mortality of the cowpea beetle. The root bark extract achieved the highest mortality of 77.50% at the dosage rate of 5% v/g within 24 h of application and its effect was significantly different (P < 0.05) from others. Also, lethal doses (LD50 and LD95) revealed that lower doses of the root bark extracts were required to achieve 50 and 95% insect mortalities when compared to leaf and stem bark extracts after 96 h of application. All the plant extracts significantly reduced oviposition and adult emergence when compared with control. The root bark extract at 5% v/g recorded the lowest seed damage and weight loss. The result obtained showed that extract of root bark of C. patens was effective in controlling C. maculatus and could serve as an alternative to synthetic insecticides.