Assessement of Aqueous Plant Extract for the Control of Kola Weevils (Balanogastris kolae & Sophrorhinus spp) (Coleoptera: Curculionidae) in Stored Cola nitida

Abstract

Kola nuts do not undergo any other additional form of post harvest processing before storage and consumption, hence there is an urgent need to develop new post harvest storage pest control strategies that are safe, of low cost, convenient to use, and environmentally / user friendly. Water extracts from seven (7) medicinal plants including Nicotiana tabacum L., Vernonia amygdalina Delile, Eucalyptus camaldulensis Dehnh, Hyptis sauvolens Poit, Cymbopogon citrtus Stapf, Lantana camara L. and Musa paradisiaca L., were evaluated for their toxicity on kola we evils development and emergence in storage. The Balanogastris kolae development and emergence from treated stored kolanuts at the various treatment levels decreased with increased concentration of the extracts applied at 25% (7.08 – 14.63), 50% (6.70 – 12.70) and 100% (4.95 – 8.75). The mean numbers of adult Sophrorhinus spp emergence at 25% treatment level (0.33 – 0.40) was not significantly different (p > 0.05) from their control treatment (0.85). However, at 50% and 100% treatment levels, all the seven plant extracts achieved a low level of Sophrorhinus spp emergence (0.15 – 0.25) and (0.13 – 0.18) respectively, which was significantly (p < 0.05) different from their control (0.85). The mean number of weevil exit holes recorded for extracts of the various plants decreased with increased concentrations of the extracts applied 25% (30.85 – 41.67), 50% (21.93 – 30.60) and 100% (16.83 -28.10). The few colour changes recorded in the stored kola nuts did not increase with the increased concentration of the extracts 25% (0.75 – 3.05), 50% (0.23 – 3.35) and 100% (0.95 – 2.48). The 7 aqueous extracts can be used at 50% and 100% treatment levels to minimally reduce the menace of kola weevils.