Abstract
A survey of gamasid mites found on small rodents was carried out in a wind-shelter belt at Tonden, Sapporo, from April 1973 to June 1974. A total of 843 gamasid mites was collected from 291 rodents (Table 1). Clethrionomys rufocanus bedfordiae (57.4% of all rodents captured), C. rutilus mikado (32.0%) and Apodemus giliacus (8.6%) were the most common. Of the gamasid mites, the majority consisted of three species, Androlaelaps fahrenholzi, Hirstionyssus isabellinus and Haemogamasus sp. (Uchikawa, 1969), totalling 72.7% of all mites. The order of dominance of the above three species of mites was equal for both species of Clethrionomys. No Laelaps clethrionomydis was collected in this locality. The infestation frequency and the number of mites on the hosts were expressed as I/M±m, where I is percent of infested hosts of all hosts examined, M mean number of mites per infested host, and m standard error. The infestation frequency of A. fahrenholzi and of Haemogamasus sp. on C. rufocanus was higher in spring and lower in autumn. However, on C. rutilus, the infestation frequency fluctuated every other season (Table 2). Of H. isabellinus, a high infestation frequency was recorded from spring to summer and no mites were found in winter on both voles. The mean number of A. fahrenholzi on each vole was high in winter, and that of Haemogamasus sp. and H. isabellinus was high in spring. Generally, Clethrionomys voles were more heavily infested by gamasid mites than A. giliacus. And there were no great differences in infestation between Clethrionomys voles, on the whole.
