Harriet Hinz
Friday, October 17, 2008 - 1:30-2:00
Garlic mustard (Alliaria petiolata) is a biennial herb of European origin, which invades forest communities in the eastern United States, the Midwest and southeastern Canada. In April 1998, a project investigating the potential for biological control was started at CABI Europe- Switzerland. Four insect species were prioritized as potential agents and studied in depth from 1999 onwards: the two stem-mining weevils Ceutorhynchus alliariae and C. roberti, the seed-feeding weevil C. constrictus and the root-crown mining weevil C. scrobicollis. Ceutorhynchus constrictus appears to be the most host specific agent so far. Apart from garlic mustard, only Brassica nigra supported development to adult. However, open-field tests showed that B. nigra is not a normal field host of C. constrictus. The two stem miners and the root-miner can develop to adult on three European species closelyrelated to garlic mustard: Peltaria alliacea, Nasturtium officinale and Thlaspi arvense and the native North American Rorippa sinuata. However, R. sinuata was not attacked by C. scrobicollis under single-choice conditions. Impact experiments revealed that C. alliariae and C. roberti reduce average shoot height and seed output of garlic mustard, while C. scrobicollis is also able to reduce overwintering survival of rosettes. A subsequently developed matrix model predicted that C. scrobicollis will have the most significant impact on A. petiolata demography. Finally, interaction experiments showed that C. alliariae and C. roberti have equal competitive abilities and that overall, no negative interactions are expected between the two stem miners and the root feeder. Therefore, all agents could be released together.
Keywords: CEUTORHYNCHUS, POST-RELEASE STUDIES