Long term dynamics of Dermanyssus gallinae in relation to mite control measures in aviary systems for layers

1. The dynamics of the poultry red mite, Dermanyssus gallinae, in aviary sy stems for layers were studied in an empirical study in Sweden between 1994 and 1997. Fluctuations were monitored with mite traps at monthly intervals during 3 laying cycles at each of 2 commercial poultry farms. 2. When mites were first detected in the system it then took about 5 months for the populations to reach equilibrium levels around which they fluctuat ed. Within flocks when the population growth was unaffected by temporary co ntrol activities, it was demonstrated that the mite populations were signif icantly denser in summer than in winter. 3. Current control methods had limited effects as mite populations were onl y temporarily suppressed. One exception was the control achieved with perme thrin impregnated plastic strips, which reduced the population at equilibri um level to approximately 22%, compared with the previous flock. 4. The distribution of mites was patchy horizontally, along the aviary syst em, at low burden whereas it became more evenly dispersed at equilibrium. 5 . Significant differences in vertical mite distributions that correlated wi th the hybrids used and their rearing conditions were also observed. In flo cks with brown hens, mites gathered at the lower tiers, whereas they were f ound at the highest tiers in association with white hens. As the hens are a ttacked mainly at night-time the most likely explanation is that the mites adjust their behavioural pattern to the birds' roosting behaviour.