The emerald ash borer, an invasive tree-killing beetle first found in N.C. last year, has a natural antifreeze agent that allows it to survive freezing temperatures to a certain degree. But once it gets below 0° F, they start to die off. A recent study (Venette and Abrahamson 2013) found that a mere 5 percent of the beetles die at 0° F, but when the temperature hits -30° F, 98 percent of beetles succumb. While North Carolina didn’t reach those extreme temperatures, the Midwest (where the beetle has been causing significant ash mortality for the past decade) did. This summer, the populations of emerald ash borer may not be as big as they have been historically.
A forest pest native to the Tar Heel State, the southern pine beetle, is used to our southern climate. Usually, populations are low and the beetles attack stressed or weakened trees. Outbreaks periodically occur, starting in weakened trees then moving to healthy trees as the population builds. When this occurs, damage is widespread and the reason this insect has been labeled the most damaging forest pest of southeastern forests. However, this recent cold snap may have frozen their ability to reach outbreak levels this year. The southern pine beetle cannot survive when temperatures reach -8° F (which parts of the state did). It’s also good news for areas to the north of us. In recent years, the southern pine beetle has made a habit of infesting New Jersey. With the cold spike, those populations may be diminished.
Generally speaking, from an invasive pest standpoint, northern and Midwestern states may benefit most from the Polar Vortex of 2014. We may still see a small amount of die-off of forest pests, especially in the western part of the state where temperatures briefly got into the range necessary to kill some insects. Temperatures in Boone, for example, reached -8° F on Jan. 7. It will be hard to determine until populations emerge. And even if insects are killed off, it’s important to note that it would only be temporary. Populations will likely rebound to ‘normal’ levels in following years.
So next time temperatures drop, try to think of the beneficial effects it could be having on forests. And be grateful that insects don’t watch the weather channel.