The double life cycle of Lepidapion argentatum, a potential candidate for the biological control of French Broom

Authors: KERDELLANT, ELVEN - European Biological Control Laboratory (EBCL); THOMANN, T - Csiro European Laboratory; VITOU, J - Csiro European Laboratory; SHEPPARD, A - Commonwealth Scientific And Industrial Research Organisation (CSIRO); GUISTO, C - University Of Genoa; SIMONOT, O - European Biological Control Laboratory (EBCL); SFORZA, RFH - European Biological Control Laboratory (EBCL)

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2019
Publication Date: 3/24/2019
Citation: Kerdellant, E., Thomann, T., Vitou, J., Sheppard, A., Guisto, C., Simonot, O., Sforza, R. 2019. The double life cycle of Lepidapion argentatum, a potential candidate for the biological control of French Broom. Biocontrol Science and Technology. 10.1080/09583157.2019.1597334.
DOI: https://doi.org/10.1080/09583157.2019.1597334

Interpretive Summary: French broom is a leguminous shrub that is an important invasive alien weed in California and nearby US states that competes with native vegetation and increases the risk of wildfires. The plant originates from the Mediterranean Region and is the target of classical biological control. Exploration for prospective biological control agents in the native region of the weed in western Europe resulted in the collection of the weevil, Lepidapion argentatum, which appears to be highly host specific. We conducted laboratory and field studies on the insect's life cycle that indicate that this weevil can develop on either seeds or inside stem galls. The ability of a weevil to develop on such different parts of the plant is highly unusual, but this means that both seedpods and young branch tips of nontarget plants must be tested to determine risk of damage by this insect. Furthermore, it is critical to know the developmental history of the adults being tested, because it affects their ability to oviposit. Future research to demonstrate that this insect is safe to release, would enable it to be used to provide environmentally-safe, sustainable control of this widespread invasive plant.

Technical Abstract: Lepidapion argentatum (Brentidae) is a weevil from the Mediterranean region mainly collected and recorded from French broom (Genista monspessulana), which is a major invasive plant in the USA, Australia and New Zealand. We conducted feeding and oviposition tests showing that the potential biocontrol agent L. argentatum has an unusual double life cycle. Overwintering adults can oviposit in either seedpods or galls of G. monspessulana. Larvae in seedpods consume one seed whereas those in stems develop inside a gall. Adults emerging from pods in spring appear to be in a reproductive diapause, whereas adults emerging from galls are able to oviposit in seed pods and produce a second generation. The mean development time of L. argentatum in stem galls is 40 ± 5 days at 25°C. The dual ability of L. argentatum to develop in stems and pods appears not to have been recorded in any other phytophagous insect, and increases its potential value as a biocontrol agent for G. monspessulana.