Mite counts from manure samples

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.