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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Invasive Species and Pollinator Health » Research » Publications at this Location » Publication #357685
Research Project: Management of Invasive Weeds in Rangeland, Forest and Riparian Ecosystems in the Far Western U.S. Using Biological Control

Location: Invasive Species and Pollinator Health

Title: Impact in quarantine of the galling weevil Lepidapion argentatum on shoot growth of French broom (Genista monspessulana), an invasive weed in the western U.S

Author
item Bitume, Ellyn
item Moran, Patrick
item SFORZA, RENE - European Biological Control Laboratory (EBCL)

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2019
Publication Date: 5/20/2019
Citation: Bitume, E.V., Moran, P.J., Sforza, R. 2019. Impact in quarantine of the galling weevil Lepidapion argentatum on shoot growth of French broom (Genista monspessulana), an invasive weed in the western U.S. Biocontrol Science and Technology. 29(7):615-625. https://doi.org/10.1080/09583157.2019.1573417.
DOI: https://doi.org/10.1080/09583157.2019.1573417

Interpretive Summary: In biological weed control, there is a need for pre-release efficacy assessments, as well as host-specificity tests for potential agents. Genista monspessulana ((L.) L.A.S. Johnson (Fabaceae), French broom) is an invasive perennial shrub in the western United States. The galling weevil Lepidapion argentatum Gerstaecker is a potential biocontrol agent for release against invasive French broom. The impact of increasing weevil density on plant height, width, leaf damage, and relative growth rate was assessed using young seedlings and either one or three weevils. The number of galls and consequent larvae were counted. Infestation by three weevils caused 48% more galls and 27% more larvae than the controls. Consequently, multiple weevils also caused a 55% and 29% decrease in plant height and width respectively. The growth rate of seedlings infested with three weevils was three times slower than the controls. The reduction in plant height and growth rate can have long lasting effects on plant development. Our results suggest that L. argentatum has the potential to cause great impact to French broom seedlings.

Technical Abstract: In weed biocontrol, there is a need for pre-release efficacy assessments for potential agents. Genista monspessulana ((L.) L.A.S. Johnson (Fabaceae), French broom) is an invasive perennial shrub in the western United States. The galling weevil Lepidapion argentatum Gerstaecker is a potential biocontrol agent. The impact of increasing weevil density on galling damage, plant height, width, leaf damage, and relative growth rate was assessed in greenhouse experiments on two to three month-old seedlings infested with either one or three weevils. Infestation by three female weevils caused 48% more galls producing 27% more larvae than did infestation with one female, while causing only 1% leaf damage and no difference in total leaf area. Infestation with multiple weevils caused a 55% and 29% decrease in plant height and canopy width respectively, while single-weevil infestation decreased height by 32% and width to the same degree as for multiple weevils. Relative growth rate of seedlings infested with three weevils was three times slower than the controls, while growth was reduced 2-fold by single-weevil infestation. Reductions in plant size and growth rate induced by weevil galling could reduce plant competitive survival to reproduction and also plant population dispersal as seedlings. Our results suggest that L. argentatum has the potential to cause impact to French broom seedlings if released in the invasive range.