Efficacite des bioinsecticides a base de l’huile essentielle de Cymbopogon schoenanthus (L.) spreng contre les punaises rouges (Dysdercus voelkeri, schmidt) en culture cotonniere au Togo

Abstract

Currently, the fight against red bugs, a pest of the cotton plant, is limited to the use of synthetic chemical insecticides. Many of the products used are persistent and their high toxicity to human health and the environment is of concern. In the search for alternatives to synthetic chemical insecticides, the aim of this research work was to evaluate the insecticidal potential of aqueous emulsions based on the essential oil of Cymbopogon schoenanthus(L.) against Dysdercus voelkeri, one of the redoubtable pests of cotton plant in Togo. Aqueous emulsions at different concentrations were used in phytosanitary treatments on cotton crop compared to vulgarized binary insecticides (lambdacyhalothrin/profenofos 15/300 gha-1and cypermethrin/acetamiprid 36/8 gha-1). D. voelkeri counts on target plants of each elementary plot revealed that the highest dose of the emulsion (6%) of C. schoenanthus essential oil and the control (vulgarized insecticide)were more effective with low bug population densities of 7.14± 1.46 and 4.86± 1.84 bugs/plant,respectively. On the contrary,the other doses (4 and 2%) of emulsions based on C. schoenanthus essential oil had in their plots respectively 39.57 ± 5.81 and 45.28 ± 3.92 bugs/plant and the control (55.71± 5.23 bugs/plant). Health analysis of the young cotton bolls that fell under the cotton plants revealed that the highest dose of the emulsion (6%) and the control reduced stings by 71.40 and 72.33 % respectively, compared to the control. Stings reduction rates in plots with treatments of 4 and 2% of the emulsion were low with rates of 55.32and22.83%,respectively. These results clearly show that the aqueous emulsion formulated and tested in the study can significantly reduce attacks of these pests. This study shows the possibility of using the essential oil of C. schoenanthus as a raw material in the formulation of biopesticide as an alternative to synthetic chemical insecticides in the control of cotton plant red bugs in Togo.