Biological control using essential oil of Ocimum gratissimum and four other biopesticides on Formicococcus njalensis, the most active mealybugs species in the transmission of CSSV (Cocoa swollen shoot virus)

A laboratory investigation was conducted to evaluate the use of Ocimum gratissimum essential oil to control the development of Formicococcus njalensis, the main vector of Cocoa Swollen shoot virus (CSSV) in West Africa. Commercial biopesticides (Squad, Agriphy, Mycotal and Banole), the essential oil of O. gratissimum obtained by hydrodistillation were compared at the concentration of 0, 1000, 2000 and 3000 µl.l-1 respectively. Ten mealybugs were directly sprayed using the different concentrations. The mortality rate of the mealybugs was evaluated by counting the number of mealybugs dead in each Petri dish 24, 48, 72 and 96 h after treatment. The highest toxicity was observed with Squad which killed all the mealybugs at each of the 3 concentrations. The second highest toxicity was observed with O. gratissimum treatment which mortality rate increased with the concentration. Indeed, a mortality rate of 39.27, 50 and 59% was observed at 1000, 2000 and 3000 µl.l-1 respectively. The third highest lethality rate was observed with Agriphy (29.36%) at 1000 µl.l-1 and with Banole (48%) at 2000 µl.l -1. At 2000 µl.l -1, Agriphy and Mycotal lethality rates were 41.4 and 5% respectively. No death was observed in the control treatment. Conclusively, environmental friendly biopesticides such as O. gratissimum and Squad can be used to control Formicococcus njalensis population, and hence limit CSSV prevalence.