DOI: 10.5061/dryad.ghx3ffbkz
title: Mite counts from manure samples

description: Pest regulation by natural enemies has a strong potential to reduce the
 use of synthetic pesticides in agroecosystems. However, the effective role
 of predation as an ecosystem service remains largely speculative,
 especially with minute organisms such as mites Predatory mites are natural
 enemies for ectoparasites in livestock farms. We tested for an
 ecosystem-level control of the poultry pest Dermanyssus gallinae by other
 mites naturally present in manure in poultry farms, and investigated
 differences among farming practices (conventional, free-range and
 organic). We used a multiscale approach involving (i) in-vitro behavioural
 predation experiments, (ii) arthropod inventories in henhouses with
 airborne DNA, (iii) a statistical model of covariations in mite abundances
 comparing farming practices. Behavioural experiments revealed that three
 mites are prone to feed on D. gallinae. Accordingly, we observed
 covariations between the pest and these three taxa only, in airborne DNA
 at the henhouse level, and in mites sampled from manure. In most
 situations, covariations in abundances were high in magnitude and their
 sign was positive. Predation on a pest happens naturally in livestock
 farms due to predatory mites. However, the complex dynamics of mite
 trophic network prevents the emergence of a consistent assemblage-level
 signal of predation. Based on these results, we suggest perspectives for
 mite-based pest control and warn against any possible disruption of
 ignored services through the application of veterinary drugs or
 pesticides.
description: The study was focused on the acarofauna of poultry manure. It was
 conducted in 20 barn henhouses (no cages, all birds on ground) distributed
 among 3 types of management practices (6 conventional, 8 free-range and 6
 organic) and located half in eastern France down to Jura mounts (Ain
 region) and half in the South of the Rhône valley (Drôme region). The
 layout of French barn henhouses is similar in the three farm types. The
 inside always contains the basic equipment necessary for the hens and
 placed on the slatted floor (high stratum) under which manure accumulates
 (low stratum). We collected five standard manure samples from
 randomly-selected points under the slatted floor, during four sampling
 campaigns in each henhouse (n= 20 x 4 x 5), to characterize manure mite
 assemblages following the methodology in Roy et al. (2017).
 Each sample consisted of 250 mL of manure taken from an area
 approximately 40 cm in diameter and 5 cm deep in a glass flask sealed with
 a rubber stopper. Exposure to saturating ethyl acetate vapours within one
 hour of sampling killed the arthropods and prevented further development
 of the assemblage. All arthropods from these samples were identified and
 counted using the Rapid Biodiversity Assessment method developed by Roy et
 al. (2017) for sorting out mite morphospecies and counting them using a
 binocular stereomicroscope.
description: Generally speaking, each flock (or batch of hens) is kept on the
 farm for one year (optimal laying period). At the end of this period, the
 hens are removed from the henhouse to make way for the next flock. For
 health reasons, a period of a few weeks' sanitary emptying, including
 massive cleaning, is systematically applied before the new flock enters
 the henhouse. Among the farms included in the study,
 flock start-up dates were deliberately varied (desynchronized), and
 consequently, so were the dates of the emptying period. In order to obtain
 data on each of the 4 seasons, we conducted 5 successive campaigns, spaced
 exactly 3 months apart, and sampled each time in all the henhouses that
 had been in operation for more than 2 months (i.e. outside the emptying
 period or at least 2 months after the entry of the new flock). Indeed, a
 sufficient accumulation of manure is necessary for the development of the
 mite community, which colonizes the poultry houses from the outside. In
 this way, we obtained about 4 sampling groups per building, but not all of
 them successively. In addition, due to sanitary constraints, one of the
 buildings had to be excluded from the sampling campaigns after 2 campaigns
 (it was contaminated with salmonella after the second campaign and we had
 committed ourselves to abandon sampling in the infected buildings in order
 to avoid spreading the pathogens).