The seek for safety: The case of the French broom weevil

Authors: SFORZA, R - EUROPEAN BIOLOGICAL CONTROL LABORATORY (EBCL); BON, MARIE-CLAUDE - EUROPEAN BIOLOGICAL CONTROL LABORATORY (EBCL); KERDELLANT, ELVEN - EUROPEAN BIOLOGICAL CONTROL LABORATORY (EBCL); TANNIERES, MELANIE - EUROPEAN BIOLOGICAL CONTROL LABORATORY (EBCL); THOMANN, THIERRY - CSIRO EUROPEAN LABORATORY

Submitted to: Biological Control Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/28/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: Guaranteeing safety of biocontrol agents has always been an issue in weed biocontrol. In fact, the purpose of releasing them in a new environment to control an invasive weed, is not to damage this environment. As a result, we studied three different aspects of a future biocontrol agent that may help to guarantee its safety. The French broom weevil attacking French broom in its Mediterranean native range, is one good example of how different approaches can help to clarify its safety and sanitary status. We first verified its taxonomic status, secondly, we measured its potential adverse feeding impact on non-target plant species, finally we ascertained the microbiological status ofthe French broom weevil. As a conclusion, our data are very encouraging for arguing that this insect could be an efficient and safe candidate for the control of the invasive French broom.

Technical Abstract: Prior to release a biocontrol agent in the introduced range against an invasive weed, several steps need to be verified to guarantee safety for the new environment. The French broom weevil, Lepidapion argentatum (Coleoptera, Brentidae), attacking French broom (Genista monspessulana; Fabaceae) in its Mediterranean native range, is one good example of how different approaches can help to clarify its safety and sanitary status. We first verified its taxonomic status as data from literature did not match with the observations that we made, such as a dual oviposition behaviour. Weevil females lay eggs both in French broom stems and fresh seedpods, a behaviour that could have belonged to two different weevil species according to literature. Integrative taxonomy was used to potentially delineate cryptic species among individuals emerging from pods and stems. Both phylogeny using a multi-locus approach and a morphological examination concurred with the hypothesis of one single species. Secondly, we measured its potential adverse impact on 36 non-target plant species including 11 species in the lupine group, closely related to the broom group. Only two lupines (Lupinus arboreus and Lupinus chamissonis) in no-choice tests showed presence of stem galls and larvae but with a minimal impact compared to controls. Additionally, no impact was observed either on lupine pods in no-choice tests or on lupine stems in choice tests, but on target brooms. Finally, field sampling of larval body remains present in seedpods and galls, and emerged adults was performed to check their health status from the source population to make sure they do not carry plant pathogens or entomopathogenic microbes. Using microbial isolation and DNA barcoding methods, eight ubiquitous saprophytic fungal genera were identified, and no entomopathogenic fungi or bacteria were evidenced. The multi-level approach presented here brings to our knowledge the confidence we could put into this potential biological control agent. We ascertained the genetic and microbiological status of the source population that could be used for a future introduction into either USA or Australia, or wherever it is a threat to the environment. In addition, although the fundamental host range revealed some non-target impacts, the ecological host range with choice tests showed zero impact on lupines. As a conclusion, our data are very encouraging for arguing that Lepidapion argentatum could be an efficient and safe candidate for the control of the invasive French broom.