EVALUATION OF SELECTED INDIGENOUS PLANTS FOR THE CONTROL OF CALLOSOBRUCHUS MACULATUS (F.) AND SITOPHILUS ZEAMAIS (MOTS.) ON STORED COWPEA AND MAIZE.

Abstract

The negative impacts of conventional chemical pesticides on both human and environment has prompted government worldwide to develop policies to reduce the use of these pesticides and have resulted in the withdrawal of many active ingredients from the market. In a bit to improve on sustainability of agriculture, biological alternatives to conventional chemicals pesticides are much sought after and needed urgently. The insecticidal potentials of plant powders from thirty five (35) selected indigenous plant botanicals using available plant parts such as bark, leaves, seed and fruits to form fifty seven (57) treatments were evaluated on Callosobruchus maculatus (Fabricius.) and Sitophilus zeamais (Moltschulsky) for a period of 24 months in the Entomology Laboratory of the Department of Crop, Soil and Pest Management, The Federal University of Technology, Akure (FUTA) under laboratory conditions of 26.8 + 2oC temperature and 65 ± 5% relative humidity. The prepared botanical powders of 1mm sized were added at different rates of dosage of application of 0.2 g, 0.4 g, 0.6 g, 0.8 g, 1.0 g and 2.0 g into 20 g of both cowpea and maize seeds in separate 250ml plastic containers with lids, against five pair of 0-24 hours emerged C. maculatus and S. zeamais adults. The experiment was replicated three times. Insects mortality were recorded at 24, 48 and72 hours post treatment for C. maculatus and 24,48,72 and 96 hours post treatment for S. zeamais. The initial screening results showed that fifty-two (52) out of the fifty seven treatments were able to cause 20% and above insect mortality in C. maculatus while thirty (30) treatments were able to evoke 20% and above insect mortality in S. zeamais. The effective powders from the results were further evaluated on oviposition and adult emergence in combinations as single, binary, ternary and quintenary combinations. These different combinations were tested on C. maculatus and S. zeamais at different rates of 0.2 g, 0.4 g, 0.6 g, 0.8 g, 1.0 g and 2.0 g per 20 g of cowpea and maize seeds. It was observed that, the different dosage of applications had different significant effects on the insects’ mortality, level of damage and adult emergence. The higher the dosage, the higher the insect mortality with concomitant reduced seed damage and adult emergence in binary combination of plant powders for both treated cowpea seeds and maize grains. Also, there is a correlation between application dosage and storage length for binary plant combinations. The effectiveness of the plant powders at dosage of 0.6 g/ 20 g was observed to be able to store cowpea seeds and maize grains for 6 months only while at 2.0 g/ 20 g of seeds was able to preserve for as long as 24 months. The ternary and quintenary plant combinations at all the experimental dosages were not able to keep the cowpea seeds and maize grains for more than 3 months may be because of the presence of multiple phytochemicals that are not compatible and are antagonistic to one another. The toxicity effect of powder from the formulation of Eugenia aromatica and Thaumatococcus daniellii on the survival of C. maculatus had the highest mortality of 100% after 72 hours post treatment at a rate of 2.0 g/20.0 g of seeds and this when compared to other treatment combinations had significant difference. At 2.0 g application rate of Eugenia aromatica and Thaumatococcus daniellii a mean value of 0.71 was observed for both oviposition and adult emergence of C. maculatus. The powder of the bark Ficus exasperata and Eugenia aromatica caused the highest insect mortality of S. zeamais. The Lethal dose analysis showed the least rate of 0.08mg/kg of E. aromatica and T. daniellii was required to cause 50% mortality of C. maculatus. This value is far less than the rate required to cause 50% mortality if either formulation constituent is used singly. A lethal dose of 1.02 mg/kg of powder from mixture of Eugenia aromatica and Ficus exasperata bark will be required to cause 50% mortality of S. zeamais, the rate which is lower than what would be required to cause 50% mortality if either botanical is used singly. The Co-Toxicity Coefficient (CTC) analysis for the effective plant combinations of E. aromatica and T. daniellii and E. aromatica and Ficus exasperata showed a synergistic relationship which had negative impact on the mortality and reproductive fitness of both C. maculatus and S. zeamais. These combinations can be recommended as part of Integrated Pest Management (IPM) programmes/ strategies for safe environment and human health.