So, what's the problem
Russian olive (Elaeagnus angustifolia) was introduced to North America in the late 19th century as an ornamental plant , for erosion control, and as a windbreak and shade tree. 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.
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 biological control project for Russian olive is therefore concentrating on natural enemies that specifically attack the flower buds, flowers or seeds in order to slow its spread without harming established trees.
What is this project doing?
CABI’s centre in Switzerland and the Biotechnology and Biological Control Agency (BBCA, Rome, Italy) initiated surveys in Eurasia in 2007 to determine whether biological control by introducing natural enemies from Russian olive’s area of origin was a feasible option. Out of 72 insect and mite species found associated with the tree in its native range, the shoot- and flower-attacking eriophyid mite Aceria angustifoliae and the shoot- and fruit-boring moth Anarsia eleagnella were prioritised for in-depth studies to assess their host range (ie. whether they could attack non-target plants if introduced in North America) and their impact on Russian olive.
The host specificity of the mite Aceria angustifoliae was assessed in an outdoor experiment in Iran and at CABI’s centre in Switzerland by attaching infested leaves to closely related test plant species and monitoring for damage. Results so far suggest that A. angustifoliae has a very narrow host range and is likely restricted to Russian olive under natural field conditions. Data have been compiled and sent to our North American collaborators for preparing a release petition.
To assess the mite’s effecton the reproductive output of Russian olive, we conducted both comparative and experimental studies. The comparative studies revealed that mite infestation reduces numbers of fruits. It is too early to collect meaningful data in the experimental study.
The moth Anarsia eleagnella has at least two generations per year: the first attacks shoot tips, while the second feeds predominantly on the fruit and damages the seeds. With regard to host specificity, no-choice tests and an open-field test in Iran showed that the host range of this species is wider than initially anticipated and appears to include several species within the family Elaeagnaceae. We plan to confirm results under open field conditions in 2019 before concluding that this species is not suitable as a biological control agent for North America.
Finally, we are planning to extend field surveys to Kazakhstan to find additional potential biological control agents, including the stem mining weevil Temnocerus elaeagni.