No deleterious effect of inundative releases of biological agents on native arthropod assemblages in poultry farms: A mesocosm experiment

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.

Population dynamics of a poultry hematophagous mite: characterization of the population growth and identification of factors of its slowdown using closed mesocosms

“…The population dynamics of D. gallinae proved to be very aggressive (> 405-fold increase in adult-like number in 35 days). In line with our previous finding, 18,26 it was much faster than predicted by the Huber model 17 (< 64-fold increase in 35 days). The plateau reached after 35 days of experimentation shows a limit imposed by the tolerance of the chick to infestation.…”

“…3). The treatment of standard (STD) mesocosms was exactly as described in Zriki et al 18, 26 . and slightly adapted for the treatment of tracking (TR) mesocosms.…”

“…All experiments were conducted in compliance with relevant guidelines and regulations on animal experimentation. The mites were sampled a few days before the start of the experiments in a laying hen barn located at Pierrelattes (France), from the same farm as for the experiments conducted by Zriki et al 18,26 . (Farm DIN).…”

“…All experiments were conducted in compliance with relevant guidelines and regulations on animal experimentation. The mites were sampled a few days before the start of the experiments in a laying hen barn located at Pierrelattes (France), from the same farm as for the experiments conducted by Zriki et al 18,26 (Farm DIN). Previous genotyping of several successive batches of dozens of mites randomly sampled at different locations and times in farm DIN showed that the poultry red mites that develop in this farm only belong to D. gallinae s.s. (more precisely, 100% of the genotyped individuals carried haplotypes of the haplogroup C, very common in French layer farms).…”

“…Two types of mesocosms were used: standard (STD) mesocosms for which mite number was estimated only at the end of the experiment (destructive counting) and mesocosms equipped with a mite tracking device (TR mesocosms) measuring mite activity during the experiment (non-destructive counting; full description available on the Zenodo repository: see section 'Data Availability') besides the destructive counting at the end of the experiment. As STD mesocosms have already been the subject of two publications by our team, 18,26 we will detail them at a minimum and further develop the description of the TR mesocosms derived from them. The structure of both types consisted of a polyvinyl chloride (PVC) cylinder 40 cm in diameter and 39 cm high for STD mesocosms or 59 cm for TR mesocosms (Fig.…”