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

The effect of permethrin impregnated plastic strips (Die No Mite Strips (TM )) 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 stri ps and thereby get the acaricide released onto their plumage, and (B) attac hed 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 p opulations, strips were mounted for 20 and 10 weeks, respectively, and mite numbers were monitored by traps. With application A an overall mite reduct ion 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 de signed 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 tim e off the host, it was not possible to control the parasite with applicatio n A. Resistance tests performed on mites from both treated and control comp artments where application A was used showed no indication of resistance to permethrin, while 95% of the mites survived a 48 h exposure to the compoun d where application B was performed. Thus, permethrin resistant mites appea red to be the main reason for the failure to control D. gallinae with appli cation B. (C) 2001 Elsevier Science B.V. All rights reserved.