Insect populations overwintering in Western Canada are likely enjoying the warmer-than-normal temperatures seen across the Prairies this winter, but the lack of snow cover could lead to increased mortality, if and when the mercury does drop.
Environment Canada forecasts for Manitoba, Saskatchewan and Alberta call for unseasonably warm temperatures over the next week, with above freezing conditions likely in many areas. Normal temperatures for the period are generally in the -15 to -20 C range.
Warmer temperatures do make it easier for many insect species to survive the winter, said John Gavloski, extension entomologist with Manitoba Agriculture, Food and Rural Initiatives. However, at the same time, a lack of snowfall can be harder on many populations, he added.
"The milder weather will be easier on a lot of insects… but not having any snowfall can also make it harder on many of them," he said.
Snow coverage data for Manitoba, Saskatchewan and Alberta show very minimal coverage in most areas.
The insects that overwinter in the soil, either as an egg, pupa or adult, rely on the snow cover to provide insulation, said Gavloski. In a year with little snowfall, such as this one, when the temperatures do inevitably drop the soil temperatures also drop sharply, increasing the mortality of insect populations overwintering.
"The lack of snowfall might lead to a lot more winter mortality," he said.
As an example, Gavloski noted that a few areas of Manitoba had problems with bertha armyworms in 2011, but those populations will be negatively affected if soil temperatures drop below -10 C for an extended time.
Grasshoppers also overwinter in the egg stage in Western Canada. The agricultural departments in all three Prairie provinces released grasshopper forecasts for the upcoming growing season over the past month.
Using data on adult populations collected in the summer of 2011, the maps show very low risk of grasshopper infestations in Manitoba and Saskatchewan in 2012.
However, there are some areas of Alberta, particularly in the north-central and Peace River regions of the province, that are showing a higher risk of grasshoppers this year, according to the maps.
The actual severity of grasshopper infestations across Western Canada in 2012 will depend primarily on weather conditions in the spring, with hot and dry conditions favouring growth and development of grasshoppers, according to the agriculture departments.
Other insects that caused problems in Western Canada in 2011, such as armyworms and diamondback moths, blow into the Prairies during the growing season, making the following year’s populations harder to predict, said Gavloski.