Challenges in using Metarhizium anisopliae for biocontrol of sugarbeet root maggot, Tetanops myopaeformis

Metarhizium anisopliae is under development as a microbial pest control agent of the Ulidiid fly, Tetanops myopaeformis (Sugarbeet Root Maggot), the most serious sugar beet pest in the United States. The fungus can be deployed by several means to create a "minefield" of infectious spores in the habitat of young larvae migrating to the developing root: ( 1) placing conidia on/in the seed coat to allow the fungus to colonize the rhizosphere; (2) applying Metarhizium granules around the seed at planting, much like insecticide granules; or (3) applying an aqueous spray of spores at or before peak fly oviposition to a narrow band of soil at the base of plants, allowing spores to soak into the top 1 cm of soil, where eggs are laid. A number of constraints could affect successful control by limiting Metarhizium survival before spores can contact larvae and influence conidial acquisition. We have examined several factors affecting Metarhizium perfonnance: conidial and fungal granule concentrations in the soil; soil type (texture), moisture, and temperature influences on efficacy and persistence; the extent of rhizoplane/rhizosphere colonization; the effect of common planting-time fungicides; and interactions with a sample of rhizosphere-associated bacteria. The value of plantingtime granule and preovipositional conidial sprays in high and low insect pressure situations was also detennined in replicated field trials.