Author
Vincent Lesieur
vincent.lesieur@inrae.fr
INRAE
Sophia Antipolis
Presenting author – Michelle Rafter
Coauthors
Thierry TThomann, CSIRO European Laboratory, Montferrier sur Lez, France
Léonore Gosselin, CSIRO European Laboratory, Montferrier sur Lez, France
Eduardo Adenesky Filho, Universidade Regional de Blumenau, Blumenau, Brazil
Marcelo Diniz Vitorino, Universidade Regional de Blumenau, Blumenau, Brazil
Andrew White, CSIRO, Brisbane, Australia
Ben Gooden, CSIRO, Canberra, Australia
Michelle Rafter, CSIRO, Brisbane, Australia
Abstract
In classical weed biological control, candidate agents are selected based on safety (high host-specificity) and efficacy (ability to reduce the target plant’s reproductive potential). While host-specificity is a prerequisite, efficacy is less commonly evaluated prior to release. We assessed both criteria for the stem-boring weevil Lixus caudiger against Erigeron bonariensis, using field observations in its native area and laboratory no-choice and choice assays. Results showed that L. caudiger consistently targets Erigeron, with a strong preference for species formerly classified under Conyza, meeting the minimum risk profile. To assess pre-release efficacy, we conducted laboratory trials at varying weevil densities, measuring adult feeding and larval impacts on plant growth, reproduction, and defence traits. Even at low densities, L. caudiger significantly reduced plant growth and strongly impaired reproduction, with a dramatic decrease in the total number of flower buds per plant. Herbivory also induced plant defence responses such as increased trichomes production, but these did not affect adult survival or larval development. Overall, L. caudiger demonstrates strong potential as a candidate biocontrol agent for E. bonariensis, supporting its consideration for importation into Australian quarantine. Our integrated approach for L. caudiger provides not only robust evidence for host-specificity but also indicates the efficacy of the agent should it be approved for release.
Keywords
Conyza
Efficacy screening
Host-specificity testing
Pre-release impact study
Stem-boring weevil
Highlights
Lixus caudiger is highly host-specific, targeting invasive Erigeron species.
Weevil greatly reduces plant growth and reproduction, even at low densities.
Pre-release testing provides solid evidence for the agent’s impact and safety.