Supplemental petition for cage-and open-field-release of the gall wasp Aulacidea acroptilonica (Hymenoptera: Cynipidae) for biological control of Russian knapweed in Canada.

The objective of this supplement is to request the release of the gall wasp, Aulacidea acroptilonica L for the biological control of he invasive plant, Russian knapweed, (Acroptilon repens L.) in Canada. This petition reviews the weed distribution, weed biology, related plant species and biological control history of Russian knapweed in Canada, as a supplement to Collier et al. (2006; attached). Collier et al. (2006) review the taxonomy, distribution, and biology of Russian knapweed for the United States, and the biology and host-range of A. acroptilonica. Information on weed taxonomy and the biology of A. acroptilonica is similar and appropriate for Canada and thus not repeated.
Russian knapweed is a non-native plant to North America of Eurasian origin that was first introduced to Canada around 1900. It is listed on noxious weed lists for BC, Alberta, Saskatchewan, Manitoba and Ontario. This plant can have significant impacts on yields of desirable crops via alleopathy and it reduces crop quality because of contamination of flour and grain products. It is poisonous to horses and forms monocultures on native range that eliminate native plant species and prevent grazing. Estimates of the total areas affected by the weed in Canada are unavailable; infestations are widespread and currently relatively small. However weed patches are very long lived once established and they appear to be on the increase in Alberta. Original descriptions of Russian knapweed in Canada indicated that the primary mode of spread was by the roots and the most of the seed was infertile. However in 2007 we found a mean of 33 % germination of Russian knapweed seed, collected from 6 sites in Southern Alberta suggesting spread by seed may be increasing. In total in North America, the weed was estimated to infest over 600,000 ha in the year 2000.
To date, biological control of Russian knapweed in Canada has been limited. The gall-inducing nematode, Mesoanguina (Subanguina) picridis, has been introduced and was established in British Columbia and Saskatchewan. However it has very limited and localized impact on the target plant. Two species of gall flies, Urophora kasachstanica and Urophora xanthippe (Diptera: Tephritidae), were petitioned for release in the US but were rejected by US Fish and Wildlife because of possible impacts on endangered species. Even prior to the USFW decision, these insects were not selected to be petitioned for release in Canada because they only affect seed production. Galls of the petitioned insect, A. acroptilonica have been shown reduce both plant biomass (by 25%) and affect Russian knapweed seed production.
The risk to Canadian and North America non-target plant species of the proposed cage release of the Uzbek strain of A. acroptilonica is very low. The Uzbek strain was not found to attack any of the non-target test plants, including species at risk or their surrogates in host-range testing. In contrast, the threat to Canadian agriculture, habitats and native plant species of allowing Russian knapweed to continue spread is significant. The only plant species of possible concern, with the release of A. acroptilonica is Centuarea americana, which is a primarily southern US species, not native to Canada. During lab host-range testing, galls were formed on this plant species once, by a separate strain of A. acroptilonica collected in Turkey. In repeated tests to try and replicate this gall formation and confirm that A. acroptilonica can complete its lifecycle on C. americana, there were no galls formed in the lab by A. acroptilonica. In addition, Centaurea americana has been exposed repeatedly, both in the lab and the field, to the Uzbek strain of A. acroptilonica and no galls have been found. Additional experiments in containment in Canada are unlikely to resolve the level of risk from the release of this insect any better then the multiple-choice open-field trials that were conducted in Turkey. As an added precaution, Centaurea americana will be tested again in the proposed field cage release.
The Uzbek population of A. acroptilonica that was screened for host-range by CABI-Europe Switzerland has been reared for 2 complete generations in the AAFC-Insect Microbial Containment Facility at Lethbridge, and has no parasitoids. I am proposing experimental cage releases of this strain of A. acroptilonica in field cages at Lethbridge and near Vulcan, Alberta, that will be monitored for establishment and impact on the target weed. As an additional test of the risk to Centuarea americana, potted plants will be placed in the field cages of the Lethbridge release and monitored for attack by A. acroptilonica. These releases are intended to establish self-perpetuating field colonies of A. acroptilonica that could eventually be used for collection and redistribution to other areas. Any decision however, to redistribute material from the initial release sites will only be made after: 1) data on the impact of A. acroptilonica on Russian knapweed, in the absence of its native parasitoids is assessed; 2) any possible attack of A. acroptilonica galls by generalist native parasitoids is determined and 3) again finding no galls from the Uzbek strain of A. acroptilonica on C. americana plants.
Contrasting the known ecological and economic risks of the continued spread and impact of Russian knapweed, with the potential risks/benefits of the release of A. acroptilonica, I am requesting the cage release of this gall wasp in Canada. The insect is specific to Russian knapweed and has potential to have an impact on the spread, seed production and biomass of this invasive plant.