Population Expansion of an Acarid Mite, Tyrophagus similis（Acari: Acaridae）due to the Presence of Soil Algae before Spinach Seeding

Abstract

It is known that an acarid mite, Tyrophagus similis Volgin, feeds on algae and grows on the soil surface in spinach greenhouses. However, no study was conducted on the effect of plowing algae before seeding to promote the mite population in the soil. We carried out observations of mite increase and spinach damage under different algae managements in 2015, both in the laboratory and greenhouses at Yamaguchi Pref., Western Japan. Propagation and plowing of algae before seeding promoted mite numbers and spinach damage in the greenhouse. This result was also supported by a supplementary laboratory experiment. In the laboratory experiment, the population of mites increased around 4 times when algae were introduced into the soil. Furthermore, additional observations demonstrated that high growth and coverage of algae on the soil surface before seeding resulted in a high population level of mites（3.5 times）in the greenhouse experiment. Our findings suggest that algae management of the greenhouse soil is an important practice for mite control in spinach production.