Abstract
Natural enemies such as predatory arthropods play an important role in controlling pest populations in agroecosystems. Laying-hen farms are agroecosystems of intensive production that incorporate a high diversity of arthropods: hen parasites and manure arthropods (predators, detritivorous, etc.). The poultry red mites Dermanyssus gallinae is the most damaging ectoparasite in laying-hen farms. Infestations with D. gallinae cause both welfare and economic problems. Dermanyssus gallinae is a nidicolous ectoparasite that lives close to its host in an environment shared by the naturally-occurring predatory arthropods in laying-hen farms.In this thesis, our objective was to improve our knowledge on the impact of native arthropods predators in laying-hen farms on D. gallinae. Based on three methodological approaches –descriptive, correlative and experimental–, the present work explored predator-prey interactions (with focus on D. gallinae) and the impact of arthropods predators on D. gallinae at three levels: 1) individual level: building the food web of native arthropods (in vitro), 2) species level: analyzing the covariation of the abundances of D. gallinae and its predators in farm buildings, 3) population level: measuring in an experimental system (hen-D. gallinae-predator) in mesocosms the impact of native arthropod predators on the development of D. gallinae populations.The analysis of native arthropods food web showed that D. gallinae is a potential prey for ten predatory species. These predators showed a significant disparity in predation frequency on D. gallinae and in their preferences for prey species between D. gallinae and detritivorous mites as alternative prey. In laying-hen farms, analysis of the relative abundances of D. gallinae and native predators supported the presence of interactions between D. gallinae and predatory species that showed high predation frequencies on it in vitro. The experiments in mesocosm allowed the development of D. gallinae, native arthropod predators and detritivorous mites. Under our experimental conditions, native arthropod predators did not show any detectable effect on the development of D. gallinae populations when other alternative prey species were present. These results suggest that, under our experimental conditions, the development of D. gallinae populations seemed to be limited by food resources (the hen) and not by the predation effect. The presence of alternative prey (detritivorus mites) may have reduced predators’ impact on D. gallinae populations. Through our experimental system, we also showed that mass-reared and commercially available predatory mites currently used to control D. gallinae in laying farms, did not have a negative effect on non-target species such as native predatory mites.Our results uncovered important gaps in our understanding of D. gallinae biology and population dynamics. These results also demonstrate the importance of further investigating the impact of alternative prey species in the absence of a regulatory effect of native predators on D. gallinae populations.