Increases in summer temperatures decrease the survival of an invasive forest insect
Mech, A. M., Tobin, P. C., Teskey, R. O., Rhea, J. R.,& Gandhi, K. J. (2018). Increases in summer temperatures decrease the survival of an invasive forest insect. Biological Invasions, 20(2),365-374. PDF.
Summary
Significant research has been done to assess how milder winters and higher mean temperatures associated with climate change have allowed invasive forest pests to spread northward and thrive in previously uninhabitable regions. However less attention has been given to how increased summer temperatures and extreme heat can hinder these same pests. This study focused on hemlock woolly adelgid (Adelges tsugae) (HWA), an invasive forest pest native to Asia and the western United States that has been devastating eastern hemlocks (Tsuga canadensis) across the eastern United States. HWA is thought to be cold intolerant and has only been moving northwards since winters have become milder. The authors of this paper turned the tables and assessed whether HWA can survive in the predicted warming and extreme summer temperatures while it is in the summer dormancy phase and also whether HWA collected from warmer regions are better adapted to survive these warmer conditions. The studies were conducted both in the lab and in the field. They found that while HWA has high survival in the temperatures that it normally encounters during the summer (<25 ºC), higher temperatures (>30ºC) resulted in up to 100% mortality. Also, the increase in temperatures led to an earlier summer dormancy phase (aestivating) in theA. tsugae that decreases the feeding on its host. There was no significant difference in the survival rate of populations collected from the southern part of their range (Georgia) and those from the northern part of their range (Maine), suggesting that HWA has not thus far been able to adapt to extreme heat in the southern portion of its range.
Take home points
While an increase in mean temperatures may lead to an overall increase in the success of invasive forest pests, some pests such as HWA may also be negatively impacted by increasing summer temperatures and extreme heat associated with climate change.
The increase in temperatures led to an earlier summer dormancy phase (aestivating) in the HWA that decreased feeding on its host tree, the eastern hemlock (T. canadensis).
So far HWA has not demonstrated the ability to adapt to higher and extreme temperatures even in the southern most portion of its range.
Management implications
Although more research is needed, HWA populations appear to be reduced during heat waves and other opportunities to further reduce the population during these extreme events could be considered.
Keywords
Impact Study; Experiment; Invasive Invertebrate; Terrestrial Habitat; Adelges tsugae; Hemlock Woolly Adelgid