Summary
The Colorado potato beetle (CPB, Leptinotarsa decemlineata) is a protected zone quarantine pest in the southern parts of Finland and Sweden. The units responsible for pest risk assessments in Finland and Sweden were requested to identify the geographical areas likely to be suitable for establishment of the CPB given a climate change scenario that covers the years 2023–2040.
Based on previous studies, the northern limit of the potential range of the CPB appears to depend, above all, on where the summer temperatures enable the development of one complete generation. To identify such areas in Finland and Sweden, we first estimated the annual growing degree day (GDD) requirement (above 10 °C) of the CPB based on the two-decade mean annual GDD in the northernmost locations where the CPB is present in Russia. The lowest mean annual GDD among these locations was 587 which was used as the GDD requirement of the CPB in this assessment. Next, we delineated the areas in Finland and Sweden where this GDD requirement was met in a recent time period (2003–2022) and in a future time period (2031–2050) assuming an intermediate greenhouse gas emission scenario, i.e., Representative Concentration Pathway (RCP) 4.5.
The results show that the GDD requirement of 587 is met in large areas in southern Finland and Sweden, and by 2040, also in central Finland and the Baltic Sea coastline. We further assessed that there are enough hosts for the CPB to enable establishment in these areas. These areas were therefore assessed as likely to be suitable for the establishment of the CPB. Importantly, they include areas much further north than the current protected zones. This result was assessed to be rather robust since even a 20% higher GDD requirement (704) was met in a much larger area than the protected zones both in Sweden (in the recent and future climate) and in Finland (in the future climate).
The greatest sources of uncertainty in the assessment are the uncertainty of the annual GDD that the CPB needs to complete its life cycle, the future climate projections, and the abundance of hosts necessary in a landscape to enable the CPB to establish.