Efficacy of Metarhizium anisopliae microsclerotial granules1

Abstract

The entomopathogenic fungus Metarhizium anisopliae has very recently been shown to produce microsclerotia (MS) – compact, heavily melanised, hyphal aggregates – in liquid media. Soil incorporation bioassays of dried MS preparations of three isolates of M. anisopliae were conducted using third instar Tetanops myopaeformis (sugarbeet root maggot) in clay and/or clay loam field soils as a model system to demonstrate efficacy. At rates as low as 23 mg MS granules/100 g dry soil, the biocontrol efficacy of MS granules of M. anisopliae Strain F52 produced in liquid media with a high carbon concentration (36 g/L) and high C:N ratios (30:1, 50:1) were superior to MS preparations produced in low carbon (8 g carbon/L) media and a high carbon medium with a 10:1 C:N ratio. Bioassays using MS formulations of M. anisopliae strains MA1200 and TM109 produced in high carbon and high C:N ratio media were superior in efficacy to the other MS production media tested. MS preparations of M. anisopliae F52 showed superior efficacy against the sugarbeet root maggot in comparison with more conventional, conidia-covered nutritive (corn grit) granules in a clay and clay soil. The MS granules were also highly efficacious against the sugarbeet root maggot at soil moisture levels as low as 0.983 A w (−2.33 MPa). Granular preparations incorporating Metarhizium MS can serve as a viable formulation for the use of this fungus against soil insects.