It's a Cold, Cruel World. But Not For Emerald Ash BorerView
There has been a lot of interest in the possibility of emerald ash borer (EAB) being killed by the record-cold temperatures the Midwest ise experiencing in early 2019, but some entomologists who’ve studied EAB for a long time are not optimistic.
Research from the University of Minnesota in 2014 suggests that below-freezing temperatures could destroy a substantial amount of EAB larvae, if the conditions were right. That could be a pretty big “if”.
“Let me put it this way,” Deb McCullough, Michigan State University forest entomologist, says. “The same record cold that hit Minnesota was also hitting the UP [Upper Peninsula] of Michigan, and EAB are still thriving very well there.”
The reason? There’s more involved with determining what’s going to freeze than just cold outdoor temperatures.
Cliff Sadof, Purdue University entomologist and EAB researcher, explains why it’s tough to determine if freezing temps are killing EAB.
IT’S ALL ABOUT ANTIFREEZE
“Insects, like people, can produce antifreezes,” he says. “As an example, on January 30 when it was just so freezing cold, if we walked outside, our nose starts to run. That’s our body’s response to the cold – it pushes that ‘antifreeze’ into our nose to keep it from freezing.
“Insects also produce antifreezes in response to the cold, but that can only work for so long, just like our nose will eventually freeze off when it’s out in the cold for too long,” he says. “It’s the same thing for insects.”
Sadof says that studies have shown that if EAB larvae are chilled to -30˚F, 97% of them will die. At -20˚F, around 75% will die, and at -10˚F, 10% will die.
COLD TEMPERATURES AREN’T ENOUGH
“The thing is, it has to be cold over a 24- to 48-hour period for that to work,” he says. “The ash trees act insulators – especially on bigger trees where the bark is thick, so it’s going to be awhile for a tree to cool down to those temperatures. They may have lost EAB in Minnesota and Wisconsin this winter, but not all of them.”
Wind chill is also not a factor when considering EAB-killing temperatures. McCullough says that the ambient temperature surrounding a tree can be warmer or colder in different places, as ambient temperature depends on factors like snow and wind cover, shade, sunlight and tree height.
“Even if a good portion of larvae die, next year when the live ones emerge, each female EAB will be laying around 50 eggs or more, so those dead larvae will be replaced quite quickly,” she said.
Howard Russell, Michigan State University entomologist, agrees.
“Insects, for the most part, won’t be affected by this cold,” he says. “They are very cold hardy.”
BUT THERE ARE EXCEPTIONS TO THE RULE
McCullough has noticed that one invasive Michigan insect has been hit hard this winter – hemlock woolly adelgid.
“We checked our research areas after those extremely cold days in Michigan [Jan. 30-31] and saw a lot of hemlock woolly adelgid mortality,” she says. “These insects live outside, so they’re more vulnerable to the cold. For us, that’s a good thing!”
Sadof has noticed similar findings in Indiana with invasive evergreen bagworms, which dangle in bags from branches, unprotected. They also lack protective mechanisms (like antifreezes) that other insects have. His research has noted that temps of -0.6˚F or less for 24 hours are fatal to the pest.
“The fiercely cold temperatures that dipped below 0˚F this winter have probably killed evergreen bagworm in many areas of Indiana,” he says. “Some of these bagworms may survive if they feed off trees within about 25 feet of buildings or pavement, because it’s warmer.”
For more information about EAB, go to www.emeraldashborer.info.
#emeraldashborer #ashtrees #invasivespecies #hemlockwoollyadelgid #climatechange
by Robin Usborne <email@example.com>
Posted February 26, 2019