Evaluation of alfalfa fields and pastures as sources of Spissistilus festinus (Hemiptera: Membracidae): Quantification of reproductive and nutritional parameters

Authors: Sisterson, Mark; Dwyer, Donal; Uchima, Sean

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2022
Publication Date: 12/7/2022
Citation: Sisterson, M.S., Dwyer, D.P., Uchima, S.Y. 2022. Evaluation of alfalfa fields and pastures as sources of Spissistilus festinus (Hemiptera: Membracidae): Quantification of reproductive and nutritional parameters. Environmental Entomology. 52(1):119-128. https://doi.org/10.1093/ee/nvac104.
DOI: https://doi.org/10.1093/ee/nvac104

Interpretive Summary: Grapevine red blotch disease is present in vineyards throughout California. The threecornered alfalfa hopper was recently identified as a vector of grapevine red blotch virus, the causal agent of grapevine red blotch disease. Because grapevine is not a primary host of the threecornered alfalfa hopper, abundance of threecornered alfalfa hoppers in vineyards depends on movement of adults from source habitats into vineyards. Accordingly, risk of alfalfa fields and irrigated pastures serving as source habitats for the threecornered alfalfa hopper was evaluated. Threecornered alfalfa hoppers were more abundant in alfalfa fields than pastures. Further, threecornered alfalfa hoppers collected from alfalfa fields were larger, heavier, and had greater energetic reserves than adults collected from pastures. Results suggest that vineyards planted in proximity to alfalfa fields are at risk for incidental infestation by threecornered alfalfa hoppers. Results will aid vineyard managers in evaluating risk of movement of threecornered alfalfa hoppers into vineyards based on composition of the surrounding agroecosystem.

Technical Abstract: The threecornered alfalfa hopper (Spissistilus festinus) is a pest of grapevine, with damage caused by transmission of grapevine red blotch virus. Because grapevine is not a preferred host of the threecornered alfalfa hopper, abundance in vineyards depends on proximity to source habitats and presence of preferred hosts in vineyard understories. The potential for alfalfa fields and pastures in the Central Valley of California to serve as sources of threecornered alfalfa hopper was evaluated by quantifying parameters associated with threecornered alfalfa hopper reproductive and nutritional status. Laboratory studies determined that the threecornered alfalfa hopper is synovigenic, emerging as an adult prior to initiation of oogenesis and that females have multiple rounds of egg production. Alfalfa fields, irrigated pastures, and vineyards were sampled monthly. Adults were observed year-round in alfalfa fields and pastures, with populations peaking in fall. Gravid females were observed from February through November. While rare, adult threecornered alfalfa hoppers were collected from 2 of 4 sampled vineyards. In spring, adults were observed in samples collected from vineyard ground cover. In fall, adults were observed in samples collected from vineyard ground cover and foliage samples. Samples collected from pastures and vineyards were male biased, whereas equal numbers of males and females were observed in alfalfa fields. Adults collected from alfalfa fields were larger, heavier, and had greater estimated energetic reserves than adults collected from pastures. Adults collected from vineyards were of above average size and had relatively high estimated energetic reserves. Results suggest that alfalfa fields are more likely to serve as sources of threecornered alfalfa hoppers than irrigated pastures and that differences in male and female behavior may affect rates of pathogen transmission.