イネ科牧草におけるムギダニの異常発生

抄録

In the early spring of 1989, an outbreak of the winter grain mite, Penthaleus major (DUGÈS), occurred in the forage grasses of the Nasu region in north-central Honshu, Japan. The mites heavily damaged 10ha of Italian ryegrass fields and caused withering of the stubs. The average number of mites per square meter was about 80, 000, with population density fluctuating from 9, 851 to 157, 120. The relationship between population density and orchard grass yields was surveyed. Dry weight of the grass per square meter with densities 32, 454 and 1, 629 were 64.5 and 145.1g, respectively.