Understanding the role social wasps play in facilitating cluster rot infections in vineyards

Grape cluster rots, pose significant challenges to growers, causing substantial economic losses and requiring high management costs annually. Despite advancements in managing some rots, the role of insects like social wasps (Hymenoptera: Vespidae) in facilitating these diseases is understudied. Yellowjackets cause direct damage to berries and facilitate microbial infection by creating entry points for vectoring pathogens.

This project investigates the role of wasps in facilitating grape cluster-rot infection by characterizing the microbial communities on field-collected wasps and grapes at four grapevine phenological stages. The study was conducted in six vineyards across South Central Wisconsin during 2023 and 2024. Three clusters per vine were aseptically collected. Wasps were sampled using dome traps with acetic acid and isobutanol lures, with five traps per cultivar. Wasps were collected weekly, identified, and counted. Grape and wasp samples were cultured and analyzed using Sanger and Illumina sequencing to identify prevalent yeasts and filamentous fungi.

In 2023, 33 unique fungal morphotypes were identified from grape samples and categorized into antagonistic agents, rot pathogens, and non-rot pathogens. Early grape phenological stages (Bloom and Buckshot) had more biocontrol agents, whereas later stages (Veraison and Harvest) showed more pathogens. Additional results revealed significant site-based differences in wasp captures, with no significant differences across cultivars. Main species were Vespula germanica, V. maculifrons, Dolichovespula maculata, and V. flavopilosa. Temporal variations highlight the seasonal dynamics of wasp populations. Future analyses will compare fungal community composition between wasps and grapes which will help inform integrated pest and disease management strategies in the Midwest