Effects of heating laying hen houses between consecutive laying cycles on the survival of the poultry red mite Dermanyssus gallinae

The poultry red mite (PRM) Dermanyssus gallinae, the most common ectoparasite affecting laying hens worldwide, is difficult to control. During the period between consecutive laying cycles, when no hens are present in the layer house, the PRM population can be reduced drastically. Heating a layer house to temperatures above 45 degrees C for several days in order to kill PRM has been applied in Europe. The effect of such a heat treatment on the survival of PRM adults, nymphs and eggs, however, is largely unknown. To determine that effect, an experiment was executed in four layer houses. Nylon bags with ten PRM adults, nymphs or eggs were placed at five different locations, being a) inside the nest boxes, b) between two wooden boards, to simulate refugia, c) near an air inlet, d) on the floor, under approximately 1 cm of manure and e) on the floor without manure. Mite survival was measured in 6 replicates of each of these locations in each of four layer houses. After heating up the layer house, in this case with a wood pellet burning heater, the temperature of the layer house was maintained at >= 45 degrees C for at least 48 h. Thereafter, the bags were collected and the mites were assessed as being dead or alive. The eggs were assessed for hatchability. Despite a maximum temperature of only 44 degrees C being reached at one location, near an air inlet, all stages of PRM were dead after the heat treatment. It can be concluded that a heat treatment of layer houses between consecutive laying cycles appears to be an effective method to control PRM.