Comparative study of field and laboratory evaluations of the ethnobotanical Cassia sophera L. (Leguminosae) for bioactivity against the storage pests Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) and Sitophilus oryzae (L.) (Coleoptera: Curculionidae)

The powdered leaves of Cassia sophera along with hot- and cold-water leaf extracts of this plant were tested in laboratory experiments in the UK and in field trials in Tamale, Northern Ghana, using traditional storage containers, to determine their inhibitory and toxic effects against Sitophilus oryzae and Callosobruchus maculatus infestation of stored rice and cowpea, respectively. Laboratory and field experiments with cowpea showed that the use of C. sophera hot-water extracts was more effective at reducing C. maculatus infestation and adult emergence on cowpea than the traditional leaf-powder application (1% and 5% w/w) or the use of a cold-water extract of C.sophera. Hot-water extracts of C. sophera might be a more effective technique of applying the plant material on to stored cowpea than using powdered C. sophera leaves, the currently used application by small-scale farmers. In contrast, experiments with S. oryzae on rice showed that C. sophera leaf powder (5% w/w) effectively reduced adult emergence in the laboratory, but this could not be confirmed under field conditions. The hot and dry climatic conditions in the field might impart a natural protection against rice infestation by S.oryzae, making the use of protectants and pesticides less necessary for farmers. This was supported by the negligible rice grain damage after 6 months of field storage and by the failure of the S. oryzae population to establish itself under field conditions. The implications of using botanicals in pest control are discussed