This rapid PRA shows that PSHB is a serious pest of deciduous trees where it has been introduced, and impacts are likely to increase as the pest continues to spread. The situation is rapidly changing, with further information about this pest being regularly published, meaning continued monitoring of the situation is required. 

Risk of entry

 Entry is unlikely on wood and bark (this category including woodchips, squared and unsquared wood), and hitchhiking and moderately likely on wood packaging material and plants for planting. 

Risk of establishment 

Establishment is unlikely, with low confidence. Several widely planted species in the UK including English oak and plane are preferred and highly successful reproductive hosts of PSHB. Climate may limit establishment, but no specific data on the temperature requirements for development of PSHB are available. 

Economic, environmental and social impact 

PSHB causes large impacts in its current range. Potential impacts in the UK are rated as small with low confidence, as it is not sure how damaging PSHB would be in the cooler climatic conditions of the UK. Even if PSHB has a slower development time in the UK, with Page 14 of 22 perhaps only one or two generations per year, successful growth of F. euwallaceae within woody hosts could still lead to decline or mortality of trees. 

Endangered area

 Oak trees in the south of England and urban amenity trees are likely to be most at risk. The southern EU member states are significantly more at risk. 

Risk management options Exclusion, through legislation, is the best risk management option. The polyphagous nature of the pest and the lack of available control products would mean eradication is unlikely to be successful if establishment occurred.

Key uncertainties and topics that would benefit from further investigation

The key uncertainties around the pest are concerned with its taxonomy, full distribution and the temperature development requirements for both the beetle and its fungus. Though the current distribution indicates that the climate in the UK will be unsuitable for the pest, other Asian ambrosia beetles have shown massive expansions in range as invasive species and, without data on the temperature requirements for this pest, potential establishment and impacts are highly uncertain. Monitoring the spread of the pest northwards in California into regions with cooler summers should provide more information on the possible impacts of the pest in Europe.