Impact of Environment on Callosobruchus maculatus (Coleoptera: Chrysomelidae) Response to Acetone Extract of Gnidia kaussiana Meisn (Thymeleaceae) and Ocimum canum Sims (Lamiaceae) Botanical Insecticides
D. Kosini *
Faculty of Medicine and Biomedical Sciences, University of Ngaoundéré, Garoua, Cameroon.
E. N. Nukenine
Department of Biological Sciences, Faculty of Science, University of Ngaoundéré, Ngaoundéré, Cameroon.
K. H. Tofel
Department of Biological Sciences, University of Bamenda, Bamenda, Cameroon.
J. W. Goudoungou
Department of Biological Sciences, University of Bamenda, Bamenda, Cameroon.
D. J. Langsi
Department of Biological Sciences, Faculty of Science, University of Ngaoundéré, Ngaoundéré, Cameroon.
M. Adamou
Faculty of Medicine and Biomedical Sciences, University of Ngaoundéré, Garoua, Cameroon.
J. P. Abdou
Department of Chemistry - Faculty of Science - University of Ngaoundéré, Ngaoundéré, Cameroon and Phytochemistry Laboratory, Institute of Medical Research and Medicinal Plants Studies (IMPM), P.O. Box 13033 Yaoundé, Cameroon.
B. Djafsia
Faculty of Medicine and Biomedical Sciences, University of Ngaoundéré, Garoua, Cameroon.
H. M. T. Ndouwe
Faculty of Medicine and Biomedical Sciences, University of Ngaoundéré, Garoua, Cameroon.
*Author to whom correspondence should be addressed.
Abstract
The response of pests to the effects of a botanical insecticide can vary spatially and temporally. To test whether efficacy of botanicals differed spatially, the insecticidal efficacy of Gnidia kaussiana and Ocimum canum against Callosobruchus maculatus was investigated in two different agro-ecological zones of Cameroon, i.e. Maroua and Ngaoundéré (sudano-sahelian and sudano-guinean zones, respectively). Experiments were, therefore, conducted to determine the insect mortality, progeny production, grain damage and weight loss in cowpea. G. kaussiana was more effective against C. maculatus in Maroua (LD50 = 0.12 g/kg at 6th day of exposure) than in Ngaoundéré (LD50 = 4.35 g/kg at 6th day of exposure). Moreover, it was more toxic than O. canum extract and neem seed oil (reference), irrespective to the agro-ecological zones. Overall, the performance of O. canum did not vary significantly between the two zones, and was slightly more active (LD50 = 4.66 g/kg) than the reference insecticide neem seed oil (LD50 = 4.89 g/kg) in Ngaoundéré in contrast to the results recoded in Maroua (LD50 = 1.44 g/kg and 2.60 g/kg, respectively for neem seed oil and O. canum at 6 days post exposure). In view of the above, there were some discrepancies in extract performance between Maroua and Ngaoundéré. Thus, the establishment of dose rates of insecticidal products formulated from G. kaussiana must be specific to an environment in contrast to those from O. canum.
Keywords: Callosobruchus maculatus, Gnidia kaussiana, Ocimum canum, pest control, agro-ecological zones