50 Session 1 Pre-Release Testing of Weed Biological Control Agents An Update on Biological Control of Invasive Hawkweeds in North America G. Cortat1, G. Grosskopf-Lachat1, H. L. Hinz1, R. DeClerck-Floate2, J. Littlefield3 and C. Moffat4 1CABI Europe – Switzerland, Delémont, Switzerland [email protected] 2Agriculture and Agri-Food Canada, Lethbridge, AB, Canada 3Montana State University, Bozeman, MT, USA 4University of British Columbia Okanagan, Kelowna, BC, Canada Abstract European hawkweeds (Pilosella spp.) have been introduced into New Zealand and North America where several species have become problematic. In the early 1990s, CABI Europe- Switzerland initiated a biological control project on behalf of the Hieracium Control Trust in New Zealand for mouse-ear hawkweed, Pilosella officinarum (L.) F.W.Schultz & Sch. Bip. (= Hieracium pilosella). Five insect species were eventually released in New Zealand. Since 2000, CABI has also been investigating natural enemies for use against invasive alien hawkweeds in North America, namely meadow hawkweed, P. caespitosa Chiov. (= Hieracium caespitosum) and orange hawkweed, P. aurantiaca (L.) F.W.Schultz & Schultz- Bip. (= Hieracium aurantiacum). In contrast to New Zealand, where all existing hawkweeds are naturalized, native Hieracium spp. occur in North America, thus limiting the number of species that can be considered for introduction. A gall wasp, Aulacidea subterminalis Niblett, which attacks the stolon tips of several Pilosella species has proven to be very specific. Regulatory authorities in the USA and Canada have recently approved release of the agent in time for releases in spring 2011. A TAG petition for a root-feeding hoverfly, Cheilosia urbana Meigen. is currently being drafted. One additional candidate agent investigated is Aulacidea pilosellae Kieffer. which galls the midrib of leaves, stolons and flower stalks of several Pilosella spp. Two forms of the wasp that differ in life history are known. Wasps located in the northern distribution range are univoltine, whereas wasps in the southern range are bivoltine. The two forms also appear to differ in their host range. Molecular analyses are currently underway to determine the level of genetic differentiation between the two forms. Apart from the candidate agents listed above, we believe that the prospects for finding further effective and safe European insects for hawkweed biological control in North America are unlikely. Should further agents be required, we suggest that pathogens, especially the rust Puccinia hieracii (Röhl.) H. Mart. should be re-evaluated. XIII International Symposium on Biological Control of Weeds - 2011.