Seasonal fluctuation in population density of phytoseiid mites and the yellow tea thrips, Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) on grape, and predation of the thrips by Euseius sojaensis (Ehara) (Acari: Phytoseiidae)

Abstract

Seasonal fluctuation in population density of phytoseiid mites and Scirtothrips dorsalis and species composition of phytoseiid mites were investigated from May to September in 1997 and 1998 in a Delaware vineyard in Osaka Prefecture. Phytoseiid mites were found in high densities from mid-July to mid-August in 1997 and from mid-July to mid-September in 1998. S. dorsalis was found in high densities from late June to late July both in 1997 and in 1998. The dominant species of phytoseiid mites investigated in 1998 were Euseius sojaensis from mid-June to mid-August and Amblyseius eharai from late August to late September. The numbers of S. dorsalis larvae consumed per hour and day by E. sojaensis were 1.4 and 5.4, respectively. The results suggest that the population increase of E. sojaensis corresponds to that of S. dorsalis and affects the population density of the thrips as a predator on grape.