Insecticidal and vertebrate toxicity associated with ethnobotanicals used as post-harvest protectants in Ghana

Six plant species (Cassia sophera, Chamaecrista nigricans, Mitragyna inermis, Ocimum americanum, Securidaca longepedunculata and Synedrella nodiflora) traditionally used in Ghana to control insect pests of stored grain and legumes were screened in the laboratory at three concentrations (0.5, 1 and 5%, w/w) against four common storage pests (Rhyzopertha dominica, Callosobruchus maculatus, Sitophilus zeamais and Prostephanus truncatus). All the plants showed some ability to control all or some of the test insect species. Levels of efficacy varied according to test concentration with the highest concentration tested providing the best control. The S. longepedunculata plant induced the highest percent mortality and was the best at reducing emergence of the F(1) generation. The six plants were also incorporated into standard rat diet at two concentrations (1 and 5%, w/w) and fed to rats over a 6-week period to assess potential deleterious effects against vertebrates. None of the plants demonstrated any neurotoxicological or neurobehavioural effects to the rats over the course of the trial. However, S. longepedunculata and C. nigricans caused a significant reduction in rat growth rate when incorporated at 5% in the diet, induced cell hyperplasia in the liver, and reduced the mean weight of the liver and kidneys, compared to the control group of rats. Kidney pathology was affected only by the 5% concentration of S. longepedunculata which caused a reduced accumulation of alpha2mu-globulin. The implications of these results are discussed in the context of farmer usage of insecticidal plants for stored product protection.