Extreme cold may wipe out high percentage emerald ash borer larvae

Here’s one resident who may welcome the extreme cold wave headed for Minnesota. Your local ash tree.

The extreme temperatures moving in with Sunday’s arctic blast may kill off a significant percentage of emerald ash borer larvae, according to one of the premier forestry experts in Minnesota.

Fig. 1. Location of United States and Canada weather  stations used in this study,and ranges of green,white,and black ash in North America according to Little (1971). R.D. DeSantisetal./Agricultural and Forest Meteorology 178–179(2013)120–128

As I gauge the incoming cold wave event, my latest read is that the Twin Cities area will see close to 84 consecutive sub-zero hours starting Saturday night, and lasting into Wednesday morning.

Model forecasts vary, but the deepest cold should peak somewhere between -20 and -26 Monday and Tuesday mornings. Here’s the latest look at the Global Forecast System model’s temperature output for early next week.


In northern Minnesota the sub-zero cold will be even deeper, and slightly longer in duration.

Image: David Cappaert, Michigan State University

Emerald ash borer and extreme cold?

Given the magnitude of the incoming cold wave, I wondered about the potential positive benefits of the extended sub-zero streak.

Lee Frelich

I’ve spoken many times about the mortality of the pine bark beetle at -40 in northern Minnesota based on discussions with University of Minnesota forestry expert Lee Frelich, director of the Center for Forest Ecology

Lee is widely regarded as a premier expert on all things Minnesota forest, including insect mortality in extreme cold.

Astute MPR News listener and Updraft reader Krista Loke got me thinking about how the emerald ash borer might fare in the upcoming cold.

Hey Paul, was just reading the updraft. Even though I never miss you in the morning with Kathy. Though I find this latest temperature dip a tough one I’m glad to see it/feel it. Didn’t we used to get cold like this for weeks at a time? And they never cancelled school! Kids have it so easy these days.

I digress…. I am wondering how cold and for what duration do we need to kill off the emerald ash bore? I thought it was something along the lines of -20 for 2 weeks straight.

Focus on the positive! I just received my first wave of seed catalogs. Time to hunker down and start planning the garden. Take care, stay warm.

Krista Loke

Great question Krista. I had my suspicions on how the extreme cold might affect the little buggers, but I went straight to the source for this one. Here’s the excellent and timely response Lee sent my way.

I think the forecast temperatures that we will experience in the next several days will cause a lot of mortality for emerald ash borer in MN. Details below–probably more than you need. I looked up the most recent research this morning, because I figured I will get a lot of questions about this over the next week.

Winter mortality for emerald ash borer is definitely temperature dependent. The larvae can supercool to a certain point, but they die if they freeze, and there is variability in tolerance among individual insects. A recent study from the Forest Service (Venette and Abrahamson–see attached) in Minnesota showed that 5% of the insects die at 0F, 34% at -10F, 79% at -20F and 98% at -30F.

Table 1. Coldest temperatures recorded in largest and smallest diameter logs used in larval
Robert C. Venette1 & Mark Abrahamson2

However, there is the question of what temperatures the insects actually experience, since they spend winter under the bark of trees, and some of them close to the ground, where they may be insulated by the bark itself and possibly by the snow.

This insulation effect can have a substantial effect if overnight minimum temperatures take a brief plunge and recover quickly. In such cases minimum temperatures under the bark can be 2-7F warmer than air temperature.

However, with prolonged cold lasting all night or, as we may experience in the coming days, prolonged cold well below zero all day and all night, then the insulating effect of bark becomes minimal.

A recently published study (DeSantis et al–see attached) integrates these factors to show where emerald ash borers are likely to have substantial mortality–see color maps in figures 2 and 3 in the DeSantis paper. There is a large area in northern MN that has a lot of ash trees that experiences temperatures cold enough to greatly limit the survival and reproduction of the insect.

That is good news for our 900+ million ash trees, many of which grow in the swamps of northern MN. However, with warmer winters likely to occur in the future, this could change. Also, the few insects that do survive the upcoming cold spell might be more resistant to cold than an average insect, and give rise to a new generation of more cold-tolerant insects, although we don’t know much about this type of selection in emerald ash borer.

In addition, as you know, there is huge variability in minimum temperature across the landscape, on south or north facing slopes, hill tops, valley bottoms.

We will know more about that over the next year, as we acquire data from our network of Hobos measuring hourly temperatures at 150 forested locations within forests in the BWCAW and Voyageurs National Park, and 150 on Isle Royale. There is also the urban heat island in the Twin Cities, which will help the insects a lot.
Lee E. Frelich
Director, The University of Minnesota Center for Forest Ecology

So for Minnesota’s ash trees, the magnitude and duration of the upcoming cold wave may be a very good thing! No doubt Lee and his colleagues will be checking in to see how the ash borer larvae fared during this extreme cold wave.

  • brnpttmn

    I love that you use weatherspark. Such a great tool.

  • del cecchi

    Using the term “historic” to refer to something that routinely happens every few years seems sort of over dramatic. But there is a trend towards “weather hysteria” with advisories, warnings, watches for regular weather events. This seems to be fed by the media and the media weather folks.

    • beekay31

      Illinois hasn’t had windchills this low since 1994. Two decades is not a regular weather event.

      • del cecchi

        It may not be regular but it is not historic.

  • dave

    I would like to know more about how an insect becomes cold tolerant?

    • Paul Sullivan

      The insects that can survive the extreme cold are the only ones that survive to pass on their genes to the next generation of ash borers.

      • Owen McMurtrey


        • Paul Sullivan

          Yeah my answer was overly simple.

    • cakyrias

      You didn’t study ANY basic science in school?

  • Deb Beasley

    In Illinois, the ash trees have been decimated. If this weather kills the little buggers, bring more of it on.

    • James Sexton

      Same here in Ohio! Any killed would be a blessing!

    • Joel Hitt

      This wonderful cold weather may be remembered as an anomaly in our warming trends over the last decades. That would be my educated guess, and I’d love to be wrong.

  • Charles Burgess

    Will the cold snap be geographically widespread enough to make a significant impact, or will they just recolonize?

  • Jeff Krebs

    The extreme cold should also help decimate the Hemlock Wooly Adelgid (HWA) populations in certain areas with extreme cold. Usually around -25 to -35 degrees C see big die off of HWA.

  • Brad

    I’d like to hear how this cold snap can kill these EABs in the US, but not kill them in their native range of Mongolia, where temperatures are well below freezing as well? It is in the negative double digits nightly there.

  • Nick di cresce

    How about the ticks (dog & deer) they have been terrible the last 3 years here in MI.

  • Carollia

    I wonder about other fauna, such as squirrels, birds, and others, what’s going to happen to them? will they be able to survive these temperatures? for how long?

  • DeAnn McClintock

    I think it is too late for my yard here in Michigan, but I am hopeful for the trees and folks in MN.

  • John A Gulsby

    Oh, for people interested enough to study the sex habits of the polar bear, John McCain!

  • treelady

    Even though part of the native range of EAB includes Mongolia, I believe DNA tests showed that our infestation originated in China. Yes, it can get cold in China but I don’t know if China gets negative double digits. Spring’s emergence will provide much more information.

    What is the prognosis for the Pine Bark Beetle? What is the negative degree data to get a sizable kill off? I’m assuming the same variables apply.

  • Scottie Ash Seed

    It’s good to see Minnesota is not making the same mistakes Illinois did when tree experts in our state sat in their office and theorized how things would unfold during the encounters between EAB & American Ash tree’s on their public parkways. Down here during the first year of the drought, these experts looked out the window in August and seen limbs on Ash trees succumbing to EAB long before fall. Since they had only witnessed the earlier years when the effect of summer borer damage was not seen until next spring, they quickly proclaimed to the press that the drought was quickly killing the EAB stressed trees.Never mind the scientific fact that our native “Bottomland” Green Ash happens to be one of the best drought tolerant tree species, especially since it leaf’s out the latest in spring, and first in fall, along with it’s drier Olive tree family origins. Imagine, hardly anyone knows this has now turned into a modern day extinction event since EAB kills young trees before seeding age, unlike Dutch Elm’s fungus which let’s trees seed until 25. Now owners in Michigan who treated their Ash tree for last 10-13 years have already been advised to lower dose rates since studies of nearby forests resulted in not one LIVE ash of any type or size, while soil was void of any seeds capable of germinating continued generations. And since live untreated Ash is Borers solitary food source, danger from bugs passes usually 12-15 years after first EAB was discovered in region. Hey MN tree owners, Green Ash has lifespan of 300, and White 600 yrs, and can be “Preventively” treated with generic 75WSB Imidacloprid 2.83 grams per DBH. Apply by mid May with rented soil injector no deeper than 4″. Allow a year and half for proper uptake on large trees. If any signs of borer damage, must inject with Tree-age” which lasts 2 to 3 years. Then switch to self applied after tree heals. Save indigenous local seeds to return species to forests someday, and Attn any communities over a century old, you have settler planted ash trees that are today only teenagers at 100-160 years old, and can be easily preserved. Chicago successfully did to 36,000 public trees, costing city $60 every three years when purchased in bulk and applied in house!

    • http://andrewsullivan.thedailybeast.com/2012/01/the-chinese-century-is-a-myth.html AmericanMillennium

      The Ash Borer is going to go into every forest that has Ash trees and kill them. It’s just going to happen. The only ones that will survive are the ones treated in cities and parks and a few thousand giants that were planted in the Midwest on farmsteads on the plains. Those Ash trees surrounded by thousands of acres of Monsanto corn and beans will survive. Many of them are up to ten miles from the nearest native ash groves and the insecticides used on beans are applied when they are in flight. Let’s hope N. Min, Wis, Turtle Mountains, ND can freeze out the onslaught.