Cold snap no challenge to bark beetle
By Quinn J. Lance
It has been cold recently in Laramie — really cold. On Feb. 2, 2011, the temperature dropped to an absurd low of 39 degrees below zero Fahrenheit; reminding all of us who are lucky enough to live in Laramie that the average low for the month of February, 8 degrees Fahrenheit, is not really all that bad. The very next day, the temperatures warmed up to a balmy 5 degrees above zero Fahrenheit as members of the 2010-2011 Environment and Natural Resources Capstone class made their way to the recently christened Robert and Carol Berry Biodiversity Conservation Center to continue work on an Environmental Assessment.
The capstone classes EA is focusing on the impacts of salvaging bark beetle kill trees in the Medicine Bow National Forest for use in the University of Wyoming’s coal fired power plant. Before breaking out into our small groups a student asked co-professor of the course, Dr. Daniel Tinker, a forest and fire ecology specialist, if the recent cold temperatures would have an impact upon bark beetles in the Medicine Bow National Forest. Tinker said the recent cold temperature would have absolutely no impact upon the mountain bark beetle.
I began to think, if temperatures as low as 39 degrees below zero Fahrenheit do not have to the potential to kill the mountain pine beetle in the month of February, what type of climatic event does it take to affect the mortality rate of the mountain bark beetle? I quickly navigated to the University of Wyoming Library’s articles and databases page to uncover the specifics of how temperature affects the mountain bark beetle. Sifting through the results, I struck gold when I came across an article, “Modeling cold tolerance in the mountain pine beetle, Dendroctonus ponderosae,” by Jacques Regniere and Barbara Bentz, published in 2007 in the Journal of Insect Physiology.
According to Regniere and Bentz, “Mountain pine beetle SCP (supercooling point) and associated cold-induced mortality fluctuate throughout a generation, with the highest SCPs prior to and following winter.” This is because the mortality rate for mountain pine beetle is more than just a function of temperature. Breaking a year in the life of a mountain pine beetle into three distinct phases clarifies this issue. The three distinct phases identified by Bentz and Regniere are:
State 1: summer state, feeding larvae that we refer to as non-cold-hardened. State 2: fall and spring state, non-feeding larvae that have eliminated ice-nucleating substances (the first phase of cold hardening). State 3: deep winter state, larvae containing high concentrations of polyols and antifreeze proteins, (Bentz and Regniere 561).
The mountain pine beetle will not be affected by temperatures in a homogenous pattern. States one and two are when the mountain pine beetle is the most susceptible to drastic drops in temperature. During state 3, the mountain pine beetle has developed the needed insulation (i.e. antifreeze proteins) and has completely purged itself of ice-nucleating substances to survive days and nights in sub-zero temperatures, (Bentz and Regniere 567).
The bottom-line; If the temperature does not drop to around the 30 below zero Fahrenheit mark prior to November or after March, the likelihood of mountain pine beetle mortality to be caused by low temperatures is highly improbable.
So where does this leave us for now? Well, as the mountain pine beetle rests comfortably inside of the phloem, encased in antifreeze for the next few months, the 2010-2011 ENR Capstone class will continue to research appropriate reactionary responses to mountain pine beetle epidemic.
Quinn J. Lance is a student at the University of Wyoming.