Evaluation of ethanol plant extract for protection of Cola nitida against kola weevils (Balanogastris kolae and Sophrorhinus spp) (Coleoptera: Curculionidae) in storage

The kola weevils Balanogastris kolae and Sophrorhinus spp. (Coleoptera: Curculionidae) are the most destructive of all kola pests. This study was designed to evaluate the protective properties of ethanol extracts of 5 plant materials each at 1x103, 2.5x103, 5x103 and 1x104 ppm, against the kola weevils on stored kolanuts. The development and emergence of adult weevils were assessed by counting newly emerged adult weevils at fortnightly intervals for 112 Days. The number of weevil exit holes on the kolanuts and the number of kolanuts with colour change in each treatment were also determined. The mean number of adult B. kolae emergence from the various extract treatments did not differ significantly from each other. However, none of the extract treatments compared effectively with the standard treatment (1.38 ± 0.25). A similar trend was observed for Sophorhinus spp., but emergence of adult weevils was extremely low (0.03 ± 0.13 to 0.34 ± 0.10), even for the control treatment (0.78 ± 0.14). There was no significance difference in the mean number of weevil exit holes recorded for all the extracts at 2.5x103, 5x103 and 1x104 ppm treatment levels. However, they all differed significantly (P < 0.05) from their control treatment (101.16 ± 11.26), but did not compare effectively with the standard treatment (8.16 ± 0.75). The mean number of kolanuts with colour changes recorded for the standard treatment (2.28 ± 0.18) differed only completely from the various treatment means of Cederela odorata (6.16 ± 0.39; 5.81 ± 0.38; 5.28 ± 0.30; 4.97 ± 0.16). Generally, there was no significant difference amongst the various extract treatments means, so none could be claimed to be superior to the other. The various extracts therefore could be proffered as alternatives to kola farmers, so as to reduce their total dependence on synthetic insecticides for kolanut storage. Storage of kolanuts at 2.5x103 ppm was found adequate and recommended taking into consideration their general protective effectiveness of the kolanuts and for economic reasons.[PUBLICATION ABSTRACT]