First mite to lead biological fight against Russian olive approved for use in Canada

More than 10 years spent researching a safe and effective biological control to fight the Russian olive may soon start paying dividends after authorities have given permission for the release of the first biological control agent – Aceria angustifoliae – against the invasive weed in Canada.

CABI, together with partners from the Biotechnology Biocontrol Agency (BBCA), Italy, the University of Belgrade, Serbia, and Ferdowsi University, Mashhad, Iran, have been researching the shoot-and-flower-attacking eriophyid mite A. angustifoliae to control Russian olive (Elaeagnus angustifolia) since 2007.

Set up of an open-field test at Ferdowsi University, Mashhad, Iran. (Credit: CABI).

Surveys in Eurasia were conducted to determine whether biological control – by introducing natural enemies from Russian olive’s area of origin – would be a feasible option to tackle the weed which was introduced to North America in the late 19th century as an ornamental plant, for erosion control and as a windbreak and shade tree.

However, it has become a significant invader of natural habitats, particularly along riverbanks, and to date has been classified as a noxious weed in four states of the western USA, a figure that is likely to increase in the near future.

Out of 72 insect and mite species found associated with the tree in its native range, A. angustifoliae and the shoot-and-fruit-boring moth Anarsia eleagnella were prioritised for in-depth studies to assess their host range. The scientists were keen to ensure that the mites would not attack non-target plants if introduced in North America and what their impact on Russian olive would be.

In 2019, CABI, together with Dr Rosemarie De Clerck-Floate from Agriculture and Agri-Food Canada (AAFC) and Dr Tim Collier from the University of Wyoming – on behalf of the USA – submitted a petition for field release of A. angustifoliae.

After supplemental information was submitted, the Canadian Food Inspection Agency has now granted permission for A. angustifoliae to be released in Canada under the authority of the Canadian Plant Protection Act and the scientists hope that field releases will take place by spring 2023.

Aceria angustifoliae damage on the shoot tips of Russian olive (Credit: CABI).

Dr Philip Weyl, Research Scientist, Weed Biological Control based at CABI’s Swiss Centre in Delémont, said, “Permission to release Aceria angustifoliae in Canada is a major step forward to having a viable biological control to tackle Russian olive in Canada and, perhaps in time, other parts of North America.

“Although Russian olive competes with native species and alters ecosystem functions, some still value it as an ornamental plant and windbreak. To avoid conflicts of interest, the project team has concentrated on natural enemies that specifically attack the flower buds, flowers or seeds of the tree in order to slow its spread without harming established trees.

“The host specificity of A. angustifoliae was assessed in an outdoor experiment in Iran and at CABI’s centre in Switzerland. Results suggest that A. angustifoliae has a very narrow host range and is likely to be restricted to Russian olive under natural field conditions.

“Field surveys in Kazakhstan are ongoing to find additional potential biological control agents, but had to be interrupted due to COVID-19 related travel restrictions. As soon as possible, we will resume surveys, specifically to find the stem mining weevil, Temnocerus elaeagni, another prioritized candidate biocontrol agent for Russian olive.”

Dr De Clerck-Floate said, “We are now eager to trial releases of the gall mite at sites in British Columbia and Alberta where Russian olive is particularly invasive in sensitive riparian habits. Based on CABI’s thorough test results, we have confidence in the agent’s potential as a safe and effective agent in curtailing Russian olive’s aggressive spread.”