A field study on the efficacy of Neem oil to control the poultry red mite Dermanyssus gallinae

The poultry red mite (PRM) Dermanyssus gallinae is a cause of major concern in laying hen flocks all over the world, due to its deleterious effects on animals (anemia, stress and decrease in production), and on the poultry industry economy. Several drugs are proven to be effective against PRM. However, the insurgence of resistance, the limited number of products to be used during the production cycle, when animals are present, and the risk that chemical residues could be retrieved in avian products or in the environment, are leading the scientific community to seek for alternative safer products, such as plant-derived acaricides. Among these, neem oil seems to be an excellent candidate, and its efficacy has been assessed on poultry birds kept in free range and conventional cages. The purpose of this study was to investigate the efficacy of neem oil against PRM in an industrial laying hen farm with high infestation level. In the farm, composed of 5 rows of cages (50 m in length), the end rows were used for treatment and control, respectively; the central row was considered as buffer areas. The product (Neem oil, 2,400 ppm azadirachtin) was diluted to 20% and it was administered by nebulization three times, at three days of interval. In order to estimate the D. gallinae population density before, during and after each treatment, mites were collected each time by placing 120 (40 per row) corrugated cardboard traps, embedded in a rigid plastic cover, outside the cages. Following trap removal, mites were frozen and their numbers were estimated as total weight. The results were analyzed through multi-factorial ANOVA; traps position and time were used as criteria predictors. Mite populations in the treated row showed a 94.65%, 99.64% and 99.80% reduction after the first, second and third administration, respectively. A reduction of mite population was observed also in buffer (59.93%, 75.68% and 83.68%) and control rows (63.24%, 80.02% and 82.27%). After 11 weeks post-treatment, the population density of the treated row was about 0.36%, whereas in buffer and control row, it was 2.82% and 5.98%, respectively. Traps position was the most significant variable (F-test, 311.69) as well as the interactive term time/traps position. Traps position showed a mean mite log-reduction of ca. 2-2.2 for the treated row, while in the control and buffer areas the mean reduction was 0.8 and 1.3, respectively. This result was independent from the effect of time and it suggests a strong bioactivity of Neem. The decomposition of the interactive term highlighted that this strong effect was mainly exerted within 10 days and persisted for more than two months after the last treatment. The reduction of the mite population also in the buffer and control row can be related to the dispersal of the product inside the shed due to the forced ventilation. A very high and long-lasting efficacy of neem-based products against PRM was observed. Future studies will focus on the possibility to reduce the administration schedule and the neem oil concentration, in order to guarantee a high and long-lasting neem acaricide performance and to overcome some unwanted effect recorded on the poultry equipment and eggs, such as the persistence of an oily film few days post-treatment.