Variazione nel tempo della sensibilità di Dermanyssus gallinae nei confronti di molecole acaricide utilizzate in campo

Dermanyssus gallinae infestation is a major threat for industrial poultry farms. The mite is worldwide diffused, and its prevalence is very high: it is reported that more than 80% of poultry farms are infested in some European Countries. The infestation leads to detriment of animal welfare and economic losses, as it negatively affects the egg and meat production. It may also contribute to the diffusion of infectious diseases as it has been widely recognized as a vector of a number of pathogens. Remarkably, D. gallinae could be also considered an occupational hazard, as it may infest the poultry farm workers. Currently, the control of D. gallinae infestation is performed by using specific drugs such as carbamates, organophosphates, pyrethroids or amidines (amitraz), but most of them can not be used in presence of live animals. Furthermore, in field and in vitro reports have been assessing the increase in acaricide resistances. In the light of these premises, we evaluated the susceptibility of field populations of D. gallinae against three acaricide drugs, namely phoxim (an organophosphate), Amitraz and -Cyalothrin (a pyrethroid). A total of 68 mite populations were collected from Italian industrial poultry farms for a four-year period (2008-2012), and their susceptibility to the selected drugs have been tested at field-use concentration (1X) and at lower (1/2X and 1/4X) and higher (2X and 4X) concentrations. The data showed that -Cyalothrin exhibits a lower efficacy if compared with the other two drugs. By comparing the effectiveness of the drugs by years, we found that resistance to Amitraz is constantly increasing since 2008 to 2012, while effectiveness of Phoxim has been decreasing since 2009 to 2010, while it has been increasing for the last two years. The mite resistance to -Cyalothrin has been decreasing since 2009 to 2011, but in 2012 its efficacy has significantly collapsed. Such trends remained the same independently by the concentrations. Interestingly, higher concentrations did not provide a significant increase of drug efficacy. On aggregate, our data show an increment in mite resistances against the most used acaricides, even if the trends are different for each drug. To avoid a further decrease in drug effectiveness, it should be advisable a turn over of drugs usually employed against D. gallinae in field. The use of drugs at different concentration than those recommended by manufacturers. Finally, the understanding of the genetic bases of the acaricide resistance may greatly help to struggle the insurgence and diffusion of resistant D. gallinae strains.