Bark beetles on pine logs: forecasting winter colonisation dynamics based on trap catches and temperature records.

Seasonality influences the abundance and activity of forest insects. Harvesting during periods of reduced activity could minimise colonisation risk on logs and reduce the need for phytosanitary treatments. We describe the winter colonisation dynamics of Pinus radiata logs in operational harvest sites in New Zealand and assess the probability of log colonisation as a function of captures in flight interception traps. After 15 days, 3% and 1% of logs were colonised by Hylastes ater and Hylurgus ligniperda (Coleoptera: Scolytinae), respectively, and 1% by Xenocnema spinipes (Coleoptera: Curculionidae). The same three species were captured in traps. Our observations showed that logs exposed for ≥ 2 weeks are predicted to have a more than 1% probability of bark beetle colonisation, whereas logs removed from forests within 24 or 48 h had predicted colonisation rates of 0.13% and 0.26%, respectively. A positive relationship between trap capture and log colonisation was also observed. Average catches of < 1 bark beetle per trap, three bark beetles per trap or ten bark beetles per trap equated to estimated log colonisation rates of < 10%, 14–98% or > 98% log colonisation. A positive relationship was also shown between log colonisation rates and temperature. A 12.3 °C temperature threshold predicted colonisation rates of 5, 50 and 95% with thermal sums of 10, 20 and 30 degree-hours, respectively. Models based on exposure time, trap catches, or environmental factors can estimate seasonal probability of insect colonisation, which aids identification of periods of low pest pressure when treatments could be avoided or reduced. [ABSTRACT FROM AUTHOR]