A fungus behind an elongate hemlock scale epizootic may provide needed biocontrol

Elongate hemlock scale (Fiorinia externa) is an invasive scale insect that infests commercially-important Christmas tree species, including spruce and fir, in addition to native eastern hemlock in forest settings. Infestation weakens trees and can cause needle yellowing and drop. Unfortunately, chemical interventions can potentially exacerbate infestation by causing declines in natural enemies. This work aims to identify fungi that naturally infect and kill elongate hemlock scales in the eastern United States for biocontrol. In August 2020, Fraser fir branches with elongate hemlock scales were collected from North Carolina and Virginia and examined for signs of fungal infection. Fungi infecting elongate hemlock scales were isolated on selective media: crawlers were almost exclusively infected. A widespread fungus infecting scales was molecularly identified as Conoideocrella luteorostrata (Clavicipitaceae, Hypocreales, Ascomycota), which is known to infect elongate hemlock scales in their natural range in southeast Asia. EF1-α, LSU and β-tubulin sequences from C. luteorostrata strains collected from different sites were identical, suggesting that this U.S. population may reflect a single introduction. We were able to confirm pathogenicity of this fungus against elongate hemlock scales in laboratory bioassays. We plan to continue our development of this fungus as a biopesticide, including characterizing its natural incidence in the eastern United States.