Pine Beetle populations not hindered by cold snap

MINERAL COUNTY – Over the last several weeks, members of the community have wondered about the status of Mountain Pine Beetle populations in response to colder than average temperatures in early December.

After prolonged low temperatures, with a daily high in low single digits and lows well below zero, some have speculated the tree-killing beetles may have frozen to death. However, according to Nancy Sturdevant, an entomologist with the forest service, this has not been the case.

The beetles are a native species to Montana. As such, they have evolved to survive the cold temperatures. According to Sturdevant, the beetles have an anti-freeze like substance in their bodies, which keeps them from freezing to death in cold winters.

“When we had these cold temperatures…by that time, the insect was already able to withstand really extreme temperatures,” said Sturdevant.

She said it would take an unusual case of extreme cold temperatures to kill the beetles. A severe cold snap in October, November or April, when the beetles were still young, could be enough to kill them. However, after the insects have had a taste of the cold as adults, they are able to withstand the cold with ease.

The area saw a few days where sub-zero temperatures were present for comparatively short periods of time. For a significant mortality rate in December or January, it would take prolonged temperatures of -35 degrees or lower for several days to make a significant difference.

However, Sturdevant said the temperatures likely killed some beetles. She said it depended on various factors like how thick the bark was and whether the tree offered enough protection from the cold. On trees with a thinner inner bark, -20 degree temperatures would be able to kill the beetles.

While it is likely some beetles died off in the cold snap, it would not have made a significant difference to the populations this year. The deaths also would have been spotty, where one landowner would have beetles die, a few miles down the road there would still be a healthy population.

“It would take killing more than 95 percent of the larvae out there to have a significant impact on the population,” said Sturdevant. “So, often we do get some wintery larvae mortality.”

However, according to Sturdevant, the Mountain Pine Beetle populations have seen a decline in recent years. While there are some hot spots, the region’s populations have decreased over the last several years. This is a good sign for the area, and there are things residents can do to help protect the trees.

The best way to impact the populations or prevent damage is with preventative thinning. The forest service recommends landowners cut down infected trees and remove them from the property before the beetles hatch. However, this is a temporary solution.

“It’s inevitable, it’s a native insect,” said Sturdevant. “If it’s not in your forest now, there’s a good chance it will be during the next 20 to 30 years.”

Removal of trees to open up an area also helps hinder the population because it adds sunlight and airflow to the area. According to Sturdevant, this makes a poor environment for pine beetles to live in. Some commercial products are also effective as protection – Carbarelli insecticide has been named as a good way to protect trees for a year.

Sturdevant said the best signs of infection were red needles on pine trees, where the crown was a faded red. “Copious amounts” of dust around the base of the tree is also a sign of the beetle’s presence. Trees with a largely green crown, but large amounts of boring dust, are likely infected and the beetles will fly around mid-June.

In this case, it is recommended the tree be removed from the property and disposed of. These trees typically hold enough beetles to infest three to five trees next year.

Pine beetle outbreaks typically occur every 10 to 15 years in Montana. Sturdevant recalled the last few years had seen decreased but sustained numbers. She estimated last year saw approximately 300,000 acres infested, which was down from the all-time high of nearly three million acres in one year.

“At this point, it seems like we’re going to continue this gradual decline in numbers or activity of pine beetle,” said Sturdevant.

However, she also said insects are very dependent on the weather. If the weather continues to be mild, or approaches warm temperatures, the area could see less of a mortality rate. There could even be some increase in the population.

Homeowners are encouraged to be proactive with beetle infestations. If trees are seen in an area, which look infected, people should look closely at their own trees for signs of infection. If self-diagnosis is not possible, it is recommended homeowners contact local foresters to have the trees checked out.