Russian knapweed (Acroptilon repens) is an herbaceous perennial native to Asia. It was accidentally introduced into North America in the late 19th century as a contaminant of alfalfa seeds. Genetic studies suggest that the origin of the North American genotypes is Kazakhstan and/or Uzbekistan. To date, Russian knapweed has spread to 45 of the 48 contiguous states in the USA, and is considered noxious in 16 western states and in one Canadian province.
In the 1970s, efforts to control Russian knapweed in the USA by biological means led to the release of a nematode species. However, this agent did not prove to be effective. Investigations on biological control of Russian knapweed were therefore resumed in 1997. CABI's centre in Switzerland has surveyed various regions in the native range to assess the herbivores associated with Russian knapweed, and to study the biology and host-specificity of selected biological control candidates. This project is carried out in collaboration with Montana State University, BBCA from Rome, Italy, and the Uzbek Academy of Science.
In spring 2008, first releases of the gall wasp Aulacidea acroptilonica (Hymenoptera, Cynipidae) were made into field cages in Canada. Field release of the gall wasp in the USA was approved by the United States Department of Agriculture (USDA-APHIS) in May 2008, but attempts to release the gall wasp during the summer failed because no adults emerged from galls. Thsi may be due to the fact that the galls were stored at cool temperature until the permit was issued. In April 2008, a chrysomelid species was detected feeding on A. repens near Samarkant, Uzbekistan. Preliminary feeding trials indicate that the host range is restricted to the genera Acroptilon and Centaurea, and potentially also the closely related genus Saussurea. To assess the impact of Cochylimorpha nomadana (Lepidoptera, Tortricidae) on Russian knapweed, we experimentally transferred freshly hatched larvae onto individual shoots in August 2007.
In summer 2008, each infested shoot was paired with a control shoot that was randomly selected within a distance of circa 2 m from the infested shoot. Attack by C. nomadana reduced above-ground biomass and seed output of A. repens by 60% and 85%, respectively, compared to the controls. In autumn 2008, the technical advisory group (TAG) recommended field release of the gall midge Jaapiella ivannikovi (Diptera, Cecidomyiidae). Galls of this gall midge were sent to the quarantine of Montana State University, USA, to establish a rearing colony. The eriophyid mite found in northern Iran in 2006 cannot be distinguished morphologically from Aceria acropilonica (Acari, Eriophyoidea) previously found in Uzbekistan, but the type of damage is significantly different. In a field experiment carried out in 2008 no attack of safflower was recorded.
2009 will set a milestone in the biological control project of Russian knapweed, since the release the two biological control agents is planned. A. acroptilonica and J. ivannikovi will be released at multiple sites in North America. Moreover, additional investigations will be made on the other candidate species mentioned above, and field surveys are planned in Iran to find new biological control candidates.