The University of Idaho has announced it will remove approximately 50 trees from the 106-year-old Shattuck Arboretum to prevent the further spread of mountain pine beetles.
Arboretum Horticulturalist Paul Warnick said that the outbreak was positively identified last summer. Warnick said the university plans to begin removing the trees as soon as possible but is presently waiting for the weather to be dry enough for them to bring the necessary equipment into the arboretum.
“The weather has not been our friend lately,” Warnick said.
Warnick said as a native species, the mountain pine beetle can always be found in the region to some degree, though the number of beetles present in the area varies from year to year. Warnick said in recent years, the trees have suffered drought stress and heat stress, which has left them weakened, and the mild winters the area has seen the last few years have allowed the beetles to thrive.
“The circumstances are just right for the population to explode and cause a problem,” Warnick said.
Warnick said the last big outbreak of mountain pine beetles occurred in 1967, and was documented in a 1969 article by two Moscow entomologists, Mal Furniss and Jack Schenk. The 1967 outbreak, like the current one, affected non-native species planted in the arboretum.
Warnick said that during summer 2014, University of Minnesota graduate student Derek Rosenberger was working on a thesis studying the problematic eastward movement of the mountain pine beetle in the U.S.
The 1969 paper documenting the 1967 UI outbreak was the only documented time the mountain pine beetle has attacked eastern North American species of pines. Because of this, Rosenberger was using it in his thesis, and emailed Warnick to ask for more documentation.
Warnick said that while corresponding with Rosenberger, he said that there were signs it could be happening again, noting that the university had lost three Scots pines during the winter of 2014 and he” had noticed several non-native long-needled pine trees showing signs of stress.
Warnick said he knew at the time it was a bark beetle infestation of some sort, but could not positively identify it. Warnick said Rosenberger asked him if he could get a positive identification on the insect, so he contacted Stephen Cook, an entomologist on campus, who positively identified the insect as the mountain pine beetle.
Stephen Cook said there are distinguishing characteristics that are used to positively identify a mountain pine beetle infestation. Cook said that when bark beetles attack a tree, the first thing that happens is the tree begins to fight back. The tree produces more resin to drive the beetles out, creating “pitch tubes,” or globs of resin on the outside of the trees, emanating from the holes where the beetles bored in.
Cook said the network of tunnels that can be seen underneath the bark of a tree are called the “gallery,” and the gallery created by each species is unique. Cook said looking at the galleries created by bark beetles is therefore a common method of identification.
“That”s pretty easy to do after you get used to it,” Cook said.
Cook said the next step is cutting out the infected trees. If the infected trees aren”t removed, the infestation will continue to grow.
Cook said that one positive thing to come out of the infestation is the opportunity to gain further scientific knowledge about beetle infestations. Cook said what interests him is that several of the tree species in the arboretum that have been attacked are species that aren”t native to western North America, so the insect is not used to them. Cook said that like the 1967 outbreak, this outbreak gives a unique opportunity to look at how this beetle does in non-native trees.
Cook said he hopes to get a small section of each of the infested trees to study in-depth. Cook said he plans to bring the sections to his lab and place them in rearing containers in order to identify the full scope of insects inhabiting those trees in addition to the mountain pine beetle.
“Again, they”re novel trees, not native to this area,” Cook said. “Any information we can get that builds on the current knowledge of what insects are using what trees should be beneficial in the future.”
Ryan Locke can be reached at [email protected]