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

Phyllocoptes gracilis Nalepa (Acari: Eriophyidae) is an important pest of raspberry plantations in Switzerland. Due to its small size and tendency to hide, it is difficult for growers to detect its presence on crops before the development of symptoms and subsequent crop 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 and monitoring. The distribution of P. gracilis within its host was studied over eight months by sampling 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 height categories on all sampling dates, there were significant differences in the distributions of the mites. Populations of P. gracilis were actively influenced by morphological changes in their host. The mite populations presented an aggregated distribution along the cane illustrated by a prevalence of mites on the upper two-thirds of the canes. Those results should be used to improve monitoring of P. gracilis by sampling specific organ types according to crop development between 60-180 cm above collar level.