Risk assessment of the bronze birch borer Agrilus anxius
Report no: 2012: 23
The Norwegian Scientific Committee for Food Safety (VKM) considers the probability of the bronze birch borer Agrilus anxius to establish and spread within Norway to be very high, if the borer enters the country. A large number of birch trees are likely to be killed, causing major economic and environmental consequences.
These are conclusion given by VKM in a risk assessment requested by the Norwegian Food Safety Authority (Mattilsynet). Agrilus anxius is the most serious pest of birch trees in North America, causing widespread mortality of birch (Betula spp.) throughout the continent. So far the pest is not known to be present outside Canada and USA. VKM considers the probability of entry to Norway to be low to medium high.
The endangered area is regarded as the forested area of southern Norway, south of Nordland County, and Pasvik in eastern Finnmark.
In 2011 the European and Mediterranean Plant Protection Organization (EPPO) decided to recommend its member countries to regulate Agrilus anxius as a quarantine pest. On this background Mattilsynet has asked for a risk assessment as a basis to decide whether the bronze birch borer should be regulated as a quarantine pest in Norway, and if so, which phytosanitary measures should be implemented to prevent entry and establishment in the country. A pest risk analysis (PRA) by EPPO in 2011 should be used as a basis for the assessment.
Agrilus anxius larvae produce galleries that disrupt phloem transport which can kill the infested tree. In Norway, the common Betula pubescens (“White Birch”) and Betula pendula (“Silver Birch”) are expected hosts, in addition to some ornamental birch species. The alpine shrub Betula nana (“Dwarf Birch”) has never been documented as a host.
Pathways and risk reducing measures
VKM has identified four potential pathways for Agrilus anxius entry into Norway: Wood chips of birch, birch wood with or without bark, birch plants for planting, and furniture and other objects made of untreated birch wood.
VKM concludes that most information given in EPPO’s PRA about risk reducing measures for each of the pathways applies to Norway as well. VKM’s conclusions concerning risk reducing measures for birch wood and chips are:
- Limited period of entry as a measure against Agrilus anxius can only be recommended on a case-by-case basis, given that the wood/chips is covered during transport, that outdoor storage is not allowed, and that all wood/chips are processed before 1 February. This measure is unfeasible when large volumes of wood/chips from different import dates are stored together and cannot be distinguished.
- Alternatively the chips can be stored for at least one year and the wood for at least two years prior to export, under strict control and conditions as described in EPPO’s PRA.
- Another method is to remove bark and minimum 1.27 cm of the outer sapwood. VKM is of the opinion that the efficiency of this measure depends on the equipment used, and it may be necessary with a case-by-case permit.
The risk assessment
The risk assessment is performed by VKM´s Panel on Plant Health, mainly by commenting on EPPO´s pest risk analysis of 2011.