Effect of permethrin impregnated plastic strips on Dermanyssus gallinae in loose-housing systems for laying hens

The effect of permethrin impregnated plastic strips (Die No Mite Strips) was evaluated on Dermanyssus gallinae populations in aviary systems for layers in Sweden. Two application strategies of the strips were tested: (A) attached in the housing system, allowing the birds to rub against the strips and thereby get the acaricide released onto their plumage, and (B) attached out of reach of the hens, at two different sites (perches and egg-belt lids) of the inner surfaces of the system, where the mites sheltered during the day. On two farms with 2030 (A) and 3384 (B) hens, and existing mite populations, strips were mounted for 20 and 10 weeks, respectively, and mite numbers were monitored by traps. With application A an overall mite reduction of 53% was observed, while with B the mean mite numbers decreased by 39% at the perches and 92% at the egg-belt lid. The strips were originally designed for caged hens afflicted by ectoparasites that stay on the host for most of their life cycle. However, since D. gallinae spends most of its time off the host, it was not possible to control the parasite with application A. Resistance tests performed on mites from both treated and control compartments where application A was used showed no indication of resistance to permethrin, while 95% of the mites survived a 48 h exposure to the compound where application B was performed. Thus, permethrin resistant mites appeared to be the main reason for the failure to control D. gallinae with application B.

Evaluation of a sampling trap for Dermanyssus gallinae (Acari: Dermanyssidae)

Traps made by rectangular pieces of 3 mm thick corrugated cardboard of four different sizes, 200 by 140 (A), 140 by 100 (B), 100 by 70 (C), and 200 by 40 mm (D), were evaluated as a sampling device for the chicken mite, Dermanyssus gallinae (De Geer). Mites were trapped during 2, 4, 6, 8, and 10 d, respectively, in a poultry house heavily infested with the parasite. Significantly greater numbers of mites were collected by trap B. Additionally, significantly more mites were collected during the sampling periods 6-10 d than by 2 and 4 d. However, with regard to trap size and sampling period, trap C, used for 2 d, collected significantly more mites per day and trap area than any of the other traps. Therefore, such a trap was suggested for monitoring population trends of chicken mites in poultry houses. The larger traps contained significantly higher numbers of mites per trap and may therefore be feasible to use in alternative, nonchemical control programs. Optimum sample size, or number of traps required to monitor population trends of D. gallinae, was also calculated. At a relative variability of 20%, and at densities of 2,000-20,000 mites per trap, approximately 11-16 of trap B and 11-19 of trap C would be adequate to monitor mites.

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 systems 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 fluctuated. Within flocks when the population growth was unaffected by temporary control activities, it was demonstrated that the mite populations were significantly denser in summer than in winter. 3. Current control methods had limited effects as mite populations were only temporarily suppressed. One exception was the control achieved with permethrin impregnated plastic strips, which reduced the population at equilibrium level to approximately 22%, compared with the previous flock. 4. The distribution of mites was patchy horizontally, along the aviary system, at low burden wlhereas it became more evenly dispersed at equilibrium. 5. Significant differences in vertical mite distributions that correlated with the hybrids used and their rearing conditions were also observed. In flocks with brown hens, mites gathered at the lower tiers, whereas they were found at the highest tiers in association with white hens. As the hens are attacked mainly at night-time the most likely explanation is that the mites adjust their behavioural pattern to the birds' roosting behaviour.

Effects of temperature and humidity on oviposition, molting, and longevity of Dermanyssus gallinae (Acari: Dermanyssidae)

The juvenile development and survival of Dermanyssus gallinae (De Geer) kept in vitro at different temperatures and humidity were investigated to obtain biological baseline data for a Swedish population. Individual females, eggs, larvae, and protonymphs were observed with regard to egg production, duration of various stages, and longevity when kept at different temperatures and relative humidities. Female mites laid eggs at temperatures between 5 and 45 degrees C with the highest numbers laid at 20 degrees C and 70% RH, but development to larvae and protonymphs was only observed at temperatures ranging from 20 to 25 degrees C. The average duration of oviposition varied from 1.0 to 3.2 d within the temperature range 20-45 degrees C but was gradually increased to 28 d at 5 degrees C. Specimens survived for up to 9 mo without access to food when kept in the temperature range of 5-25 degrees C. Temperatures > 45 degrees C and at -20 degrees C were found to be lethal. Longevity was similar for females and protonymphs kept at 30 and 45% RH, but it was enhanced at 70 and 90% RH for protonymphs. This study showed that D. gallinae can survive for a long time without feeding if the microclimate is suitable, but it does not thrive at low relative humidities and at temperature extremes. This indicates that changing of the abiotic conditions in infested poultry houses could be a possible measure to reduce mite populations.

Prevalence of the poultry red mite, Dermanyssus gallinae, in different types of production systems for egg layers in Sweden

This study was undertaken between May and December 1994 to investigate the prevalence of hematophagous mites in Sweden. A particular aim was to establish the relationship between occurrence of mites and certain types of production systems for egg layers. Initially a postal questionnaire study was performed. Some months later this was followed up by inspections, sampling, and interviews on farms. The only mite species found was the red poultry mite, Dermanyssus gallinae. Although this species was found to be present in cage batteries, deep-litter systems, and backyard flocks, it was less prevalent among birds housed in cages. About 4% of the cage systems were found to be affected both according to the results of the postal inquiry and from the field study. However, discrepancies in prevalence were found when comparing the results obtained with these two investigations regarding alternative, deep-litter systems and backyard flocks. According to the inquiry, 21% of the deep-litter flocks were afflicted whereas 33% were found to be afflicted in the field investigation. Among the backyard flocks, 19% were afflicted whereas as many as 67% of the flocks were found to be afflicted upon inspection. These discrepancies were probably due to the fact that the situation had actually changed in some farms during the study period, but possibly also to inherent methodological errors. Farmers were also interviewed with focus on methods of husbandry and control strategies. Most farmers answered that they were combatting the mites by cleaning the empty houses and using chemicals such as organophosphorous compounds, carbamates, and synthetic pyrethroids. In several instances the problems were still not solved despite these curative or preventive measures. A control program for D. gallinae is suggested by regular screening and certification of the ectoparasite status of the birds before their transfer to production sites.