Questions and Answers: Wasps as biological control agents for Emerald Ash Borers
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The Canadian Food Inspection Agency (CFIA) has approved four species of wasps as biological control agents for use in Canada in an attempt to reduce the impact of Agrilus planipennis, the emerald ash borer (EAB), which has been destroying Canada's ash trees. EAB is not native to Canada and has few natural enemies here.
The four species of wasp are: Tetrastichus planipennisi (T. planipennisi), a member of the Eulophidae wasp family; Spathius agrili (S. agrili) and Spathius galinae (S. galinae), members of the Braconidae wasp family; and Oobius agrili (O. agrili), a member of the Encyrtidae wasp family. The approval of these wasps is part of a long term strategy designed to reduce the population of EAB and reduce the destruction of Canada's ash trees. Only T. planipennisi, O. agrili, and S. galinae are being released in Canada at this time. Although S. agrili was approved for release, evaluation of release data in the United States later indicated that S. agrili is not able to establish a population and persist north of 40°N latitude, and therefore would not be suitable for pest control in Canada.
The release of the wasps will be closely monitored through ongoing scientific studies evaluating wasp establishment and spread, as well as their impacts on EAB populations.
What does "biological control" mean?
The classical "biological control" strategy is the introduction of a natural enemy from the initial home range of the pest species into the new expanded range. By introducing the natural enemy into the pest's new range it is hoped that the re-establishment of the natural enemy-prey relationship will reduce the introduced pest's populations to a more sustainable level. All four species of wasps cause considerable mortality to EAB in their native ranges of China and Russia.
What do the wasps look like and do they sting?
Tetrastichus planipennisi, S. agrili, S. galinae, and O. agrili are very small species of wasps, all under 4.0 mm in length. They do not sting humans.
How do the wasps kill EAB?
The wasps drill beneath the bark of ash trees where Tetrastichus planipennisi will deposit eggs within the larvae of host insects and S. agrili and S. galinae deposit their eggs on the surface of the host larvae. Oobius agrili lay their eggs inside the eggs of EAB which are located on the surface of the ash tree's bark.
When the wasps' eggs hatch, the young wasps feed on the host egg or larvae, thereby killing them. The wasps will not eliminate populations of EAB entirely, but it is hoped that they will reduce the population to a point where EAB is manageable in the Canadian environment.
How will the wasps be introduced to Canadian forests?
Tetrastichus planipennisi, O. agrili, and S. galinae have been introduced into Canadian forests at 19 different sites across Quebec and Ontario. Releases are currently being conducted by Natural Resources Canada – Canadian Forest Service, with cooperation and assistance from local conservation authorities and the provincial forest health teams in Quebec and Ontario. All wasp specimens from 2013-2016 were generously provided from the USDA-APHIS rearing lab in Brighton, Michigan. In 2017 USDA-APHIS once again provided many of the released specimens; however, in that year a Canadian colony of T. planipennisi was created, producing approximately 3500 specimens for release.
Wasps are released when their host (EAB) is in the appropriate stage of development; this is based on modelling data using temperatures and estimated developmental stages of EAB. For T. planipennisi and S. galinae there are six releases in a season; three late in the spring and three late in the summer. For O. agrili, there are three releases throughout the mid-summer when EAB eggs should be present. Tetrastichus planipennisi and S. galinae are released at the sites by suspending blocks of ash wood containing wasp pre-pupae (infested EAB larvae) from trunks of EAB-infested trees. Oobius agrili is released by placing wasp infected EAB eggs on filter paper; these papers are folded and placed in clear plastic containers with a screen mesh on the opening. The wasps will emerge from the larvae/eggs and fly off in search of other EAB to target. Almost 100 000 wasps have been released in this manner since 2013.
Will these wasps attack other insects?
Tetrastichus planipennisi very specifically targets EAB, while S. agrili, S. galinae, and O. agrili may occasionally attack other species similar to EAB; however, no major side effects are anticipated for non-target organisms.
The risk and potential impact of EAB warranted the use and release of S. galinae, O. agrili and T. planipennisi. While T. planipennisi is expected to attack only EAB larvae, the other species can sometimes attack other Agrilus borers. Laboratory experiments have shown that S. galinae and O. agrili highly prefer EAB as a host, in comparison to other Agrilus species. Risks to native Agrilus borer species were considered prior to release and were evaluated to be very low based on a CFIA review of potential risks. The North American Plant Protection Organization developed standards and protocols for EAB management and also considers that the impact of S. galinae and O. agrili on native Agrilus species will be of no significance.
How are biological control agents approved?
If a Canadian resident wishes to import into Canada biological control agents which have not yet been approved for release in Canada, they must first submit a petition to the CFIA, following specific guidelines.
The petition is reviewed by a Biological Control Review Committee. This committee may include taxonomists, ecologists, and other scientists, and specialists from federal and provincial governments and Canadian universities. The petition is also reviewed by representatives from the United States Department of Agriculture and from Mexico's Ministry of Agriculture. All comments are taken into consideration before the committee makes a recommendation to the CFIA to approve or deny the request.
Once the petition is reviewed and the committee provides their recommendation to the CFIA, the Chief Plant Health Officer for the CFIA makes the final decision. A letter is sent to the applicant advising them of the decision.
A CFIA Permit to Import under the Plant Protection Act would be required in order to import any of these species into Canada.
Who made the application in this case?
Natural Resources Canada made the application, which the CFIA approved.
- Emerald Ash Borer – Questions and answers
- Pest Fact Sheet: Emerald Ash Borer
- D-12-02: Import Requirements for Potentially Injurious Organisms (Other than Plants) to Prevent the Importation of Plant Pests in Canada
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