Integrated Biological Control of the Sugar Beet Weevil Asproparthenis punctiventris with the Fungus Metarhizium brunneum: New Application Approaches

The mass occurrence of the sugar beet weevil (Asproparthenis punctiventris, previously 12 Bothynoderes punctiventris) has been endangering sugar beet cultivation in Austria for centuries. Ex- 13 acerbated by climatic and political changes (warmer, drier spring and limited access to chemical 14 pesticides), new approaches are needed to counter the problem. The aim of our work was to test 15 whether the bioinsecticide Metarhizium brunneum Ma 43 (formerly M. anisopliae var. anisopliae BI- 16 PESCO 5/F52) can be used as a sustainable plant protection product against the sugar beet weevil. 17 Our goal was to control the pest in all its development stages through multiple applications. There- 18 fore, GranMetTM-P, a granular formulation of M. brunneum Ma 43, was applied in spring to establish 19 the fungus in the soil, whereas GranMetTM-WP, a liquid formulation of the production strain, was 20 used in early summer on trap ditches and leaves to target the adult weevils. Soil and plant samples 21 as well as weevils were collected during the planting season from the trial sites, to evaluate the 22 development of the fungus and the mycosis of treated weevils. In addition, data on hibernating 23 weevils and their emigration from untreated field sites was collected. In all field sites, the Metarhi- 24 zium spp. abundance increased above the background level (< 1,000 CFU g-1soil dry weight) after 25 application of the product. With increasing number of treatments per plot, and thus increased con- 26 tact possibility between pest and the fungus, a rise in the mycosis rate was observed. In conclusion, 27 the various Metarhizium application strategies, which are already available or in testing, must be 28 implemented to ensure control in both old and new sugar beet fields. Metarhizium is a further asset 29 in the successful control of this sugar beet pest.