Storage mites in the work environment of farmers

Occurrence of storage mites was studied in cow houses and hay stores on 19 farms, most of which were located in eastern Finland. On two farms we did a monthly follow-up. Mites were extracted from hay by sieving, using the so-called "water trap" and for longitudinal analysis, with a warm extractor. The mites isolated in the water trap were identified under a microscope. Contrary to previous Finnish findings, there apparently were more mites in cow houses than in hay stores. In cow houses there were an average of 1,650 mites per gram of dust and in hay stores about 1,100 mites per gram of dust. Acarus siro was most abundant in cow houses (67% of all the mites found in cow houses) and more than 1,000 mites/g of sample material. The second most numerous was Tydeus spp. (178 mites/g of sample material). After that, Lepidoglyphus destructor, Tyrophagus longior, Glycyphagus domesticus occurred in about equal numbers. In hay stores Tydeus spp. was slightly more common (341 mites/g of sample material) than Acarus siro (317 mites/g of sample material). Lepidoglyphus destructor (64 mites/g of sample material), Glycyphagus domesticus (60 mites/g of sample material) and Mesostigmata (57 mites/g of dust) occurred in about equal numbers. According to the analysis based on one farm the number of mites in hay stores decreased considerably from September to February. Based on four measurements in the cow house of another farm, however, no steady trend of longitudinal variation could be found. Mites were most abundant at the beginning of January. There were few or no mites in bales of dry and unmoulded hay.