Weather patterns determine success rates of two biocontrol agents on Cytisus scoparius in the USA

• Published in: Entomologia experimentalis et applicata 2024-11, Vol.172 (11), p.1024-1032
• Main Authors: Bode, Robert Frederick, Cervantez, Olivia
• Format: Article
• Language: English
• Subjects: Biological control; biological control agents; Brentidae; brooms; Bruchidae; Bruchidius; Bruchidius villosus; Chrysomelidae; climate; Coleoptera; Complementarity; Curculionidae; Cytisus scoparius; environmental variability; Exapion fuscirostre; Fabaceae; habitats; Indigenous species; Introduced species; Invasive species; Legumes; niche; Niche overlap; Niches; Plant tissues; Population growth; Seeds; species; Success; target species; Weather; Weather patterns; weed control; weevils
• ISSN: 0013-8703; 1570-7458
• DOI: 10.1111/eea.13494

To be effective, a biocontrol agent must survive and persist in the same habitat as the target species and reduce target population growth. When multiple biocontrol agents are used against a single invasive species, they may each perform better under a subset of the habitat in which the target lives. This complementarity allows for a more consistent level of control and a higher resilience to environmental variability. Two species that feed on the same plant tissues would compete, but niche partitioning in the native range may be replicated when both species are introduced to the invasive range. When biocontrol agents are released, they may self‐sort to perform best in their respective niches. We hypothesized that two biocontrol agents—Scotch broom seed beetle, Bruchidius villosus (Fabricius) (Coleoptera: Chrysomelidae) and Scotch broom seed weevil, Exapion fuscirostre (Fabricius) (Coleoptera: Brentidae)—that both feed on seeds of the invasive legume Scotch broom, Cytisus scoparius L. Link (Fabaceae), would be impacted differently by different weather conditions and plant traits, and would show different success rates at field sites with different conditions. We used a 5‐year study to reveal that the two biocontrol agents are not uniformly distributed in the field and that weather and plant factors influence their success. We confirmed that weather conditions of the previous year influenced biocontrol agent attack rate and found that weather patterns at a field site may predict the impact of each biocontrol agent. When multiple biocontrol agents are deployed to control an invasive species, the success of each is determined by individual niche preferences. We investigated two biocontrol agents—Bruchidius villosus (Coleoptera: Chrysomelidae) and Exapion fuscirostre (Coleoptera: Brentidae)—that feed as larvae on the same tissue of the invasive legume Scotch broom, Cytisus scoparius (Fabaceae). Previous research suggested that competition limits biocontrol success. We found that weather conditions and plant‐specific factors influenced the success of each agent.