Distribution of the eriophyoid mite Phyllocoptes gracilis (Acari: Eriophyidae)on raspberries (Rubus idaeus) in Switzerland

Abstract: Phyllocoptes gracilis Nalepa (Acari: Eriophyidae) is an important pest of raspberryplantations in Switzerland. Due to its small size and tendency to hide, it is difficult forgrowers to detect its presence on crops before the development of symptoms and subsequentcrop damage. The objective of this study was to characterize the intraplant distribution of P.gracilis on raspberry canes to optimize the sampling design for mite detection andmonitoring. The distribution of P. gracilis within its host was studied over eight months bysampling specific organ types at three height categories along infested raspberry canes.Although the presence of P. gracilis was observed in all organ types and at all heightcategories on all sampling dates, there were significant differences in the distributions of themites. Populations of P. gracilis were actively influenced by morphological changes in theirhost. The mite populations presented an aggregated distribution along the cane illustrated by aprevalence of mites on the upper two-thirds of the canes. Those results should be used toimprove monitoring of P. gracilis by sampling specific organ types according to cropdevelopment between 60-180 cm above collar level.