First Report of Hirsutella thompsonii as an Entomopathogenic Fungus of Hemp Russet Mite (Aculops cannabicola) in Kentucky

Abstract

Hemp russet mite (HRM, Aculops cannabicola) is one of the most damaging indoor pests of hemp ( Cannabis sativa). In 2021, HRM was identified in hemp research trials at the University of Kentucky. Beginning in September, large numbers of darkened (black/brown), dead HRM were observed on leaves. Fungi resembling Hirsutella thompsonii were isolated from symptomatic HRM. Fungal identity was confirmed by sequencing a fragment of the internal transcribed spacer (ITS) of the rDNA. To validate pathogenicity, HRM-infested hemp leaves were inoculated with H. thompsonii. Infection was confirmed by day 8 of the experiment. Twenty-eight percent of the HRM in the inoculated treatment became black/brown by day 14. Considering limited options for management of HRM on indoor hemp production, further research is warranted to improve understanding of the potential use of H. thompsonii as a management tool.