May biocontrol agents artificially selected for their aggressiveness improve crop protection?

In agroecosystems, the efficiency of biocontrol agents could be improved through the artificial selection of specific traits that would enhance their zoophagy level. The aim of this study was to evaluate the impact of artificially selected populations of the omnivorous predatory bug, Nabis americoferus, on the tarnished plant bug, Lygus lineolaris, in organic strawberry crops. Six populations of N. americoferus were selected according to their aggressiveness, three were composed of highly aggressive individuals, whereas the other lines contained docile individuals. The first hypothesis was that, since aggressive predators display a higher attack rate, aggressive lines would exhibit a higher pest control and a better crop protection than docile lines. The second hypothesis was that, when two biocontrol agents species are used conjointly, the presence of at least one docile population would generate a higher synergy between both species. N. americoferus populations were released in an experimental strawberry field, with or without a second intraguild predator, the Anthocorid, Orius insidiosus. Results support the first hypothesis that the aggressive lines generate a better pest control and a better strawberries crop protection than docile lines but only at low pest density. The second hypothesis is neither supported nor rejected since the combination of docile lines and O. insidiosus led to a better pest control at high pest density, but led to a reduced crop protection at low pest density. Our study shows that the artificial selection of aggressiveness has the potential to improve the effectiveness of biocontrol programs.