On the move Species may change, but the flea beetles’ spread across the Prairies is nearly complete
Flea beetles are already costing Prairie farmers $300 million a year and their populations are growing, an entomologist with Agriculture and Agri-Food Canada says.
Julie Soroka told a recent Alberta Canola Industry Update seminar scientists don’t know why the beetle species populations are shifting, but they do know the populations are rising, particularly for the striped flea beetles.
“I did not see high numbers of striped until about five years ago, but what we get now is primarily striped,” she said.
Striped flea beetles are increasing all across the Prairies. Numbers of other species are also increasing, Soroka said. In Brooks, there was a definite increase in striped flea beetles over the four years. “These trends also occur in the other two provinces. Northern Saskatchewan and northern Manitoba are also predominantly striped. In central Saskatchewan, striped beetles are now becoming more dominant over crucifer beetles,” she said.
There are three species of flea beetles commonly found on the Prairies. Two of the beetles are originally from Eurasia and the third is from the circumpolar regions.
The striped flea beetle, first reported in New York City in 1776, can be found in the boreal transition zone, the northern portions of the Prairies and the Peace Country. Forty years ago, the striped flea beetle was found throughout all regions of the Prairies except southern Alberta.
The crucifer flea beetle is a much more recent introduction to North America and first appeared in British Columbia in the 1920s. “It rapidly spread across the Prairies, becoming a common pest of cruciferous vegetables in the ’30s and ’40s. By the time rapeseed became prevalent, it flourished very quickly and became a traditional rapeseed pest,” Soroka said.
Forty years ago, the crucifer beetle was common in all three provinces, but was not found in central and northern Alberta and the Peace Country. Hop flea beetles can be found all over the Prairies, in very low numbers.
The beetles are primarily controlled by chemical means. “Almost all the canola seed that goes into the ground in the Prairies is coated with an insecticide for the control of flea beetles,” Soroka said. Foliar sprays can be used if seed treatments fail or are ineffective.
All registered seed treatments in Canada are neoniticanoids. The striped flea beetle is less resistant to these treatments than the crucifer flea beetle.
Soroka, who was involved with a survey to map flea beetle species in Western Canada and North Dakota, said the preferential mortality might be creating the shift in populations. Researchers placed a series of yellow sticky traps along shelterbelts and other areas where flea beetles overwinter.
“We had a series of five, 10 or even 20 traps that we changed weekly, or more frequently if populations were high, for periods from seed emergence to about four weeks after,” she said. Some fields were surveyed for short periods, and others for the whole summer, from 2007 to 2011. Three hundred site locations from across the Prairies, North Dakota and the B.C. Peace were included in the study.
Crucifer flea beetles were the most common at 139 sites. In 21 sites, striped flea beetle was the most prevalent. About 147 sites had some form of stripe and only four had hop flea beetles.
Soroka noted a definite increase in striped flea beetles in Manitoba over the length of the study. Striped flea beetles are also increasing in the Alberta Peace region as canola acres increase. In central Alberta, four out of five sites showed a primary concentration of striped flea beetles.
“If there was a species shift, it occurred prior to 1997,” she said. “Species are definitely site specific and we don’t know why a particular species occurs in a particular site.”