Abstract
Augmentative biological control relies on the inundative release of natural enemies of pests that are usually mass-reared in the laboratory. This practice substantially reduces the environmental impact of pest control in agriculture by reducing the use of insecticides. However, there are many reasons to expect more or less deleterious effects on biodiversity: if the enemy is not specific to the pest, the release of large populations of predators can directly affect native assemblages through the predation process itself and/or through competition with their native counterparts. In addition, mass-reared populations of enemies generally come from gene pools that are different from native populations and may, through the effects of hybridization, alter their population dynamics. On the other hand, during mass rearing, populations of natural enemies to be released are subject to different selection pressures from those in the field and may be less adapted than native populations to farm ecosystems. These effects are generally very difficult to assess in agro-ecosystems themselves due to the multiplicity of factors. In order to assess the effects of inundative releases of generalist predatory mites on native assemblages that colonize poultry houses from the surrounding environment, we conducted an experiment over several generations of mites using mesocosms mimicking a piece of a henhouse (mite-proof units, each housing one hen). No deleterious effects on native populations of Androlaelaps casalis and Cheyletus spp. have been detected from the mass introduction of marketed populations of A. casalis and C. eruditus. The mass introduction of marketed predatory mites against D. gallinae appears to be compatible with the conservation of native arthropod assemblages. The mass-reared populations of A. casalis and C. eruditus did not establish their populations under conditions which otherwise allowed their native counterparts (same taxa) to do so