Wednesday, February 12, 2014

Is the cold weather this winter going to help with our invasive insect pests?

Woke up this morning to the third blast or arctic air that has gripped our region this winter.  As I write this it is a chilly 5 degrees, was minus 1 F when I woke up.  Scientists are calling this the Arctic Vortex.  So can these frigid temperatures help control some of our most problematic insect pests?  Extreme winter temperatures are one of nature’s ways of controlling animal populations and distribution.  

Many animals, including insects, have developed adaptations to survive extreme conditions, some migrate, others grow thicker fur, still others hibernate.  Many insects and other arthropods have adapted to survive freezing temperatures by producing and storing their own internal antifreeze, elthylene glycol.  Invasive forest insects thrive in woods because they been introduced into an environment with no natural controls.  Being introduced into foreign countries their populations grow unchecked since the natural controls found in their native lands are not present.

Invasive insects that have evolved in warmer climates aren't likely to survive in extreme winter cold.  Although complete mortality isn't likely, I would expect to see a temporary decline in number of some species like hemlock wooly adelgid for example.  The real question is....How cold is cold enough to really affect these invasive populations in Pennsylvania?  I provided some answers below.  Looks like we may have impacted hemlock wooly adelgid some but the emerald ash borer needs much colder temperatures to cause mortality, closer to -13 degrees F.

Cold Hardiness of Emerald Ash Borer, A New Perspective (USDA Forest Service)
"Naturally infested logs were held outdoors in St. Paul, MN (low winter air temp = -18°F) and near Grand Rapids, MN (-29°F) for ca. 5.5 weeks. Approximately 40% of larvae from logs in St. Paul were inactive or brown, both evidence of death; approximately 90% of larvae from logs near Grand Rapids"
Cold Snap is no Snow Day for Emerald Ash Borer Management (University of Minnesota Extension 2014) 
"Data collected from the winters of 2009-2012 indicate that a substantial fraction of emerald ash borer larvae may die as temperatures fall below -20°F. At that temperature, mortality should be about 50%. Mortality rates increase quickly to about 90% as temperatures approach -30°F."  

Regional Responses of Hemlock Wooly Adelgid to Low Temperatures (Entomological Society of America)
"For all months and sites, mortality increased as temperature decreased, and no survival occurred among those from the Central and Southern sites exposed to −22 and −31°F.  In January and February, ≤3% of the adelgids collected from the Northern site survived −22°F, and none survived −31°F in January or March.  In Northern sites only 14% survived exposure to 5°F in March.  In all sites the actual percentage of adelgids that survived after exposure to 5°F decreased 50–60% from January to March."

Science Friday (Jan 10, 2014) produced a radio interview with US Forest Service research biologist, Rob Venette.
"Colder winter weather may have you bundling up, but it can be really bad news for some invasive insects. Research biologist Rob Venette discusses which invasive insects may not make it through the winter and how climate change has affected their distribution."

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