The beneficial insects are attracted to shelled-out canola seeds; their larvae prey on soft-bodied pests such as cutworms
Northern Alberta canola growers who found large numbers of beetles while harvesting last year’s crops this spring have no reason to worry.
The ground beetles are a beneficial species merely taking advantage of shelled-out canola seed, said Agriculture Canada senior research scientist and entomologist Kevin Floate.
A photograph he received this spring taken north of Edmonton showed thousands of beetles congregating in fields.
“From the photograph I knew pretty much exactly what they were because we’ve seen this before,” said Floate.
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“The last time we saw it was I think about 2010 and again in the same region, northern Alberta. A lot of canola was left unharvested in the field and then the following spring there was large numbers of these beetles and then in August of that same year there was an even larger peak of these same beetles.”
There are many species of carabidae ground beetle and Floate said this type has no common name. It is black and seven to eight centimetres long.
“This particular beetle is a beneficial beetle. It feeds on the seeds of plants, particularly seeds in the brassica family, so the same plant family as canola.
“They’re not a pest of canola. They don’t typically climb up in the plant and eat the seeds but if the seeds are lying on the ground, they’ll eat the seeds and they’ll build up a lot of fat stores.”
The plump beetles are then able to lay many eggs so producers who saw large numbers this spring should be prepared to see even higher numbers this fall when those eggs hatch.
Floate said the beetle larvae eat grasshopper eggs, cutworms, wireworms and other soft-bodied pest insects. The adults eat mostly seeds.
“They are not an economic pest insect in any sense. The only time that you could consider them a pest is when they’re prevalent in very large numbers and then they become a nuisance pest.”
That happened in at least one Alberta case Floate can recall, when large numbers of beetles moved into a new subdivision and into one home where their multitudes forced a family to temporarily vacate.
He and colleague John Spence of the University of Alberta published a paper about the high numbers reported about 10 years ago.
“We hypothesize that the abundant food supply enhanced fat stores in adults prior to overwintering, with a two-fold effect. First, a larger than normal number of adults survived to emerge the following spring. Second, the fecundity of overwintered females was unusually high,” wrote Floate and Spence in a paper published in The Coleopterists Bulletin.
“When the progeny of these females emerged as teneral adults in large numbers in fields that were planted to canola in 2009, but not in 2010, they moved into surrounding areas in search of food. Whatever the cause of these unusually high numbers, numbers returned to normal modest levels in 2011.”
Floate said he would welcome photos and other information about plentiful ground beetles. A typical farm would likely have at least a dozen and possibly as many as 80 different species of ground beetles and all the Alberta species are beneficial.
“We like to see ground beetles. If you have a lot of ground beetles in your backyard or in your fields or on your acreage, it’s actually a good thing. It suggests that you’re doing something right.”
Floate can be contacted at kevin.floate@canada.ca.
