Tackling Japanese knotweed in Switzerland

Overview

Results

The team

Related information

So what's the problem?

Some members of the Polygonaceae family are the world’s worst invasive plants, including Japanese knotweed (Fallopia japonica); a particular problem in riparian (river bank) habitats and construction areas in Europe and North America.

In 2003, a consortium of partners formed a project management board to examine the potential for the biological control of Japanese knotweed, first in the UK and later on also in North America. CABI’s centre in the UK was tasked with carrying out the research. In April 2010, after much debate, the first biological control agent, the psyllid Aphalara itadori, was released at a few selected sites in the UK.

Capitalizing on the knowledge and scientific data gathered to control Japanese knotweed in the UK and North America, we used Aphalara itadori as a case study to assess the risks of an accidental or deliberate introduction of a weed biological control agent into Switzerland.

What is this project doing?

Through this project we will complement previous tests made in the UK and in the USA on the host range (which plants are accepted for oviposition and support development) of the psyllid – Aphalara itadori – by testing members of the plant family Polygonaceae (to which Japanese knotweed belongs) that are either native to or cultivated in Switzerland. Since both the risk perception as well as the risk assessment of classical biological control is still in its infancy in Switzerland, and the family Polygonaceae is relatively small, we aim to test all native members of the family that have not been tested as part of the host-range testing conducted in the UK.

The bioassays will be done under no-choice (exposing only one plant species to A. itadori) and multiple-choice conditions (exposing several plant species) in the quarantine facility of CABI’s centre in Switzerland. Plant species to be tested include: seven species and two subspecies of the family Polygonacaeae that are native to Switzerland, local varieties of the two related crop species buckwheat (Fagopyrum esculentum) and rhubarb (Rheum rhabarbarum) as well as various genotypes of the highly invasive Fallopia x bohemica, a hybrid of F. japonica and F. sachalinensis.

Results so far

In early June 2012, A. itadori was hand-carried from CABI in the UK to the quarantine facility of CABI’s centre in Switzerland. A rearing colony of A. itadori was established successfully and adults started emerging after 30 days. Within a month over 800 freshly emerged adults were transferred to new culture cages.
Between August and December 2012, no-choice oviposition and development tests were established with three Rumex species native to Switzerland, and with F. japonica as control. Potted plants were exposed to five pairs of psyllids during five days each. All control plants received eggs and survival rate to adult was about 40%. Some replicates of the Rumex species received eggs, but at a much lower number than F. japonica (420 vs. 8-14 eggs on average) and when eggs hatched, nymphs died before they reached the second instar. Tests will be continued throughout the winter as long as fresh test plant material will be available.

Project Executive