Effects of Groundcover Preservation around Japanese Pear Trunks on the Seasonal Occurrences of Spider Mite（s Acari: Tetranychidae）and Their Natural Enemies Including Phytoseiid Mites（Acari: Phytoseiidae）

Abstract

To examine the effects of groundcover preservation around tree trunks in Japanese pear orchards on the seasonal occurrences of spider mites and their natural enemies, we compared their densities at two study sites, each of which includes two plots with weeds（weed plot）and without weeds（control plot）, in Chiba Prefecture in 2016 and 2017. The phytoseiid mites were the most dominant natural enemies observed on the trees. The densities of phytoseiid mites and spider mites on the trees were, respectively, higher and lower in the weed plots than in the control plots. The mean density of yellow tea thrips, Scirtothrips dorsalis Hood, on the trees was also higher in the weed plots than in the control plots. Some phytoseiid mite species were commonly observed on both groundcover around the tree trunks and pear trees throughout the survey period, suggesting contributions of the phytoseiid mites supplied from the groundcover in spider mite control on the pear trees