Seasonal Changes in Mite Populations in Rural Granaries in Japan1

Abstract

Seasonal changes in mite populations were studied in 336 samples of rice, wheat, barley, grain debris, and rice straw from the field, areas adjacent to granaries, granary floors, straw bags, and metal drums in 2 farmhouses and 3 rural granaries in Shiga prefecture, Japan, during June, September, and October 1966, and February 1967. The mites were identified to species or genus; their frequency on each cereal, seasonal frequency, and abundance in each habitat were recorded. Thirty-four genera with more than 49 species of mites, several of which were undescribed, were identified. Glycyphagus destructor (Schrank), Cheyletus eruditus (Schrank), Tyrophagus putrescentiae (Schrank), Cheletomorpha lepidopterorum (Shaw), Tarsonemus spp., and Tydeus spp. were the commonest mites on granary floors and were the most abundant in summer and generally scarce in winter. Of these species, only G. destructor maintained large populations through autumn and winter in all granaries. Large populations of Tyrophagus putrescentiae and Tarsonemus spp. during autumn and winter were observed in only 1 granary. More than 19 species occurred in stored grain. The 3 commonest mites, i.e., those present usually in small numbers in 100%–19% of the cereals in bags and drums, were, in descending frequency: on rice— G. destructor, Tyrophagus putrescentiae and Cheyletus eruditus; on wheat— C. eruditus, G. destructor, and T. putrescentiae; on barley— G. destructor, Tarsonemus spp., and Tyrophagus putrescentiae. All these mites appeared in grain samples throughout the year, although their numbers per sample were in most cases progressively lower from summer to winter. The 6 commonest mites on granary floors were represented in rice straw in the field. It is suggested that the infestation of stored grain and grain products originates primarily in the field and secondarily from unclean granary floors in rural areas where it spreads to urban granaries and grocery stores.