Inventories of the Main Insect Pests of Stored Corn and Repellent and Insecticidal Effects of Sapwood and Heartwood Extracts from Wood Côte d'Ivoire against Sitophilus zeamais Motschulsky (Coleoptera, Curculionidae)
Appolinaire Bley Bley-Atse *
Laboratory of Industrial Processes and Synthesis of the Environment and New Energies, National Polytechnic Institute Félix Houphouët-Boigny, P.O. Box 1313 Yamoussoukro, Côte d’Ivoire and Wood Sciences Laboratory, Department of Forestry and Environment, Higher School of Agronomic Sciences, University of Antananarivo, P.O. Box 175, Antananarivo 101, Madagascar, Côte d’Ivoire.
Armand Nahoulé Adja
Laboratory of Entomology and Agricultural Zoology, Higher School of Agronomic, National Polytechnic Institute Félix Houphouët-Boigny, P.O. Box 1313 Yamoussoukro, Côte d’Ivoire.
Florence Bobelé Niamké
Laboratory of Industrial Processes and Synthesis of the Environment and New Energies, National Polytechnic Institute Félix Houphouët-Boigny, P.O. Box 1313 Yamoussoukro, Côte d’Ivoire.
Jean Louis Lepetit N’guessan
Laboratory of Industrial Processes and Synthesis of the Environment and New Energies, National Polytechnic Institute Félix Houphouët-Boigny, P.O. Box 1313 Yamoussoukro, Côte d’Ivoire.
Hakim Abdel Aziz Ouatarra
Laboratory of Industrial Processes and Synthesis of the Environment and New Energies, National Polytechnic Institute Félix Houphouët-Boigny, P.O. Box 1313 Yamoussoukro, Côte d’Ivoire.
N’Guessan Jean Claude Yao
Laboratory of Industrial Processes and Synthesis of the Environment and New Energies, National Polytechnic Institute Félix Houphouët-Boigny, P.O. Box 1313 Yamoussoukro, Côte d’Ivoire.
Mathias Danho
Laboratory of Entomology and Agricultural Zoology, Higher School of Agronomic, National Polytechnic Institute Félix Houphouët-Boigny, P.O. Box 1313 Yamoussoukro, Côte d’Ivoire.
Augustin Amissa Adima
Laboratory of Industrial Processes and Synthesis of the Environment and New Energies, National Polytechnic Institute Félix Houphouët-Boigny, P.O. Box 1313 Yamoussoukro, Côte d’Ivoire.
Nadine Amusant
CIRAD ED Department, UMR Ecofog, PO Box 701, 91310 Kourou Cedex, France.
*Author to whom correspondence should be addressed.
Abstract
Background: Cereals play a central and important role globally in food security, nutrition and energy. Sitophilus zeamais Motschulsky is without doubt the most devastating insect pest of agricultural stocks and is resistant to synthetic chemical pesticides. The search for botanical products with low toxicity for the environment and for living beings has intensified considerably. Forestry operations produce large quantities of waste that remain under-exploited, posing a real environmental problem. Studies have shown that tropical tree species synthesis biomolecules in their heartwood that are responsible for their natural resistance and could be highly effective against insect pests.
Objectives: The aim of this study was firstly to carry out an inventory of insect pests on stored maize and secondly to assess the repellent and insecticidal activity of hydroalcoholic extracts of Nauclea diderrichii, Mansonia altissima and Milicia excelsa against Sitophilus zeamais.
Method: Stored maize samples were collected, insect pests were identified, and their relative abundance was calculated. Hydroalcoholic extracts of sapwood and heartwood were then tested, in comparison with a synthetic chemical insecticide, Protect DP (1.5% pyrimiphos-methyl and 0.1% deltamethrin), on S. zeamais to evaluate their insecticidal activity (mortality, LD₅₀, TL₅₀) and repellency at different concentrations, using a randomised experimental design with three replicates.
Results. The inventory showed that S. zeamais with a Relative Abundance (Ra) of 51.06% (Ra ≥ 10%) and T. castanenum with an Ra of 43.61% were abundant species. Hydroalcoholic extracts of sapwood from N. diderrichii, M. altissima and M. excelsa resulted in mortality rates of 80-96.67%, 76.67-88.33% and 66.67-81.67% respectively. The mortality of heartwood extracts from these same woods varied respectively from 58.33 to 95%, from 66.67 to 95% and from 36.67 to 78.33%. The LD50 of sapwood extracts was between 0.0093 and 0.0289 and the TL50 ranged from 3.5 to 6.2 days. The LD50 of heartwood extracts was between 0.050 and 0.1435 g/mL and the TL50 varied from 1.8 to 0.5 days. The repellency rate ranged from 26.67 to 96.67% after 1 hour and from 50 to 93.37% after 2 hours' exposure to the extracts tested.
Conclusions. The toxicity of the extracts is due to the presence of the main secondary compounds present in hydroalcoholic wood extracts. These results demonstrate the potential of wood extracts for controlling insect pests of stored foodstuffs.
Keywords: Wood extracts, repellent, insecticide, stock pests, Côte d’Ivoire