author(s)
François Ndosinvian Vandi, Raoul Borkeum Barry, Albert Ngakou and Elias Nchiwan Nukenine

abstract
The effectiveness of aqueous leaves extracts of Lippia rugosa, Annona senegalensis and Jatropha curcas were used for the control of thrips (Megalurothrips sjostedti) on two cowpea varieties (Bafia and Lori) under field conditions in the Cameroonian agro-ecological zone I (Modélé) and II (Dang). Trials were arranged in a completely randomized block with eight treatments each of which was replicated four times. There were seven insecticide treatments in addition to a negative control. Cowpea (V. unguiculata) plants were sprayed at flowering thrice at five days interval. Data collection consisted of counting/evaluating the population density and dynamic of adults and larvae thrips as affected by treatments, and evaluating the seed yield at harvest. As the results, all the bio-insecticide treatments generally reduced the density of larvae and adult thrips population above 95%, as much as the Decis. Thrips population density was averagely the same at Dang (11.72 ± 1.54) and Modélé (10.71 ± 1.63) in 2017, but was instead higher at Dang (9.27 ± 1.44) in 2018 than at Modélé (5.37 ± 1.35). Insect density was more elevated on the Bafia variety (10.71 ± 1.63 in 2017; 4.77 ± 0.88 in 2018) than on the Lori variety (6.53 ± 0.98 in 2017; 1.22 ± 0.82 in 2018) at Modélé. Cowpea seeds yield (kg/ha) of Lori variety was significantly (p <0.0001) improved by treatment J. curcas (1066.87 ± 43.66) in 2017, compared to treatment A. senegalensis + J. curcas (1457.27 ± 126.62) in 2108. Cowpea Bafia variety recorded the highest yield at Modélé (365.55 ± 29.21) than at Dang (316.08 ± 36.68) in 2017, with lower yields obtained in 2018. After Decis, A. senegalensis + J. curcas was the best of all bio-insecticides in reducing the cowpea thrips, thus improving cowpea seeds yield of the two studied cowpea varieties at Modélé and Dang during the two cropping seasons.