Conidial production, persistence and pathogenicity of hydromulch formulations of Metarhizium brunneum F52 microsclerotia under forest conditions

Abstract

Microsclerotia granules of Metarhizium brunneum Petch strain F52 (Hypocreales: Clavicipitaceae) in a hydromulch formulation (water, wheat straw, and tackifier) were sprayed onto bark or wood samples, which were subsequently exposed on tree trunks for 4–30d, during two spray trials in 2013 and six spray trials in 2014. Microsclerotial granules in this formulation continued to produce many infective conidia over a 30d period in a forest. Greater conidial production was associated with periods of increased temperature, relative humidity and rainfall. When F52-hydromulch-treated samples, in the 2014 spray trials, were evaluated against adult Asian longhorned beetles, Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae), in 2 d-quarantine bioassays, insect mortality varied greatly for males (14–92%) and females (56–100%). Highest conidial densities (5.5×106conidia/cm2) were reached after 20–30d in the field and at these densities, female beetle median survival times ranged from 15.5 to 21.5d. Males died significantly slower in all spray trials. The continued increase in conidial production by microsclerotia in hydromulch over time suggests that reapplication of a potential product in the field might only need to occur after 6weeks.