A Novel Approach to Tally Aculops cannabicola (Acari: Eriophyidae) for Field and Laboratory Studies

The hemp russet mite, Aculops cannabicola (Farkas) is a key pest of hemp (Cannabis sativa L.). Given its microscopic size, estimating the size of its populations can be a major limitation to control this pest. Here, we describe a method to count A. cannabicola using photographs taken with a handheld digital microscope. We compared the consistency and strength of the relationship between photographic- and microscope-based counts of mites from infested plants. Among the three sections of the leaflet, the maximum consistency levels were observed in the proximal (50%) and middle photographs (50%). However, it reached from 64% to 100% when the three sections were considered. Photographic and a microscope-based counts were positively correlated (>0.7). A single photograph can be a good predictor of the total mites per leaflet, however, using two pictures (proximal and middle sections) will increase the consistency of the abundance of A. cannabicola per leaflet. A minimum of 22 leaflets per sampling event can support a strong correlation between the microscope and photographic counts. Our method requires low budget and training and takes short time (0.4 to 1.3 min per leaflet) to count mites per sample. Additionally, photographs can be stored on a smartphone, computer, or tablet, allowing users to share, store and process the photos. This method simplifies counts of A. cannabicola on hemp for research purposes and provides a practical tool for growers to assess mite populations for management decisions. In addition, it may be useful for monitoring eriophyid mites on cultivated plants.