Flea beetles on the move

More and more non-native flea beetles are spreading into canola country, causing all kinds of problems for growers

Flea beetles are not the usual suspects when it comes to crop damage in canola, but they can be one of the most costly, says Keith Gabert, agronomy specialist with the Canola Council of Canada, which estimates annual crop losses in North America from flea beetles in excess of $300 million.

“Flea beetles are not the insect pest that we think of first in canola, but they are present in all canola fields,” explains Gabert. And while it’s difficult to predict the amount of damage they can do, they have the potential to wipe out an entire canola crop.

Flea beetles aren’t a new threat to farmers and most canola seeded on the prairies is treated, so why are we still seeing economic losses from this pest? Experts believe that part of the problem may be a population shift of certain species of flea beetles.

Flea beetles are found throughout North America — across the U.S. Great Plains including North Dakota, South Dakota, Montana and northwestern Minnesota; the Canadian prairies; the Peace River region of B.C.; as well as parts of eastern Canada.

In western Canada, three species of flea beetles are known to attack canola. The hop flea beetle (Psylliodes punctulata) is native to Canada and found in low numbers across the prairies. The crucifer (Phyllotreta cruciferae) and striped (Phyllotreta striolata) flea beetles were introduced to North America from Eurasia more than a century ago and are now a major cause for concern for canola producers in the west.

Historically, the crucifer species is dominant across the drier, southern canola-growing areas and has pushed striped flea beetles to the northern parkland and Peace River regions.

However, Julie Soroka, research scientist and entomologist with Agriculture and Agri-Food Canada (AAFC) in Saskatoon, has observed a recent southward shift of the striped flea beetle. “You could almost see a movement front of the striped flea beetle proceeding southward over the last 10 years or so,” she says.

One theory for this geographical shift is that canola seed treated with neonictinoids has shown to provide less control over the striped flea beetle than the crucifer flea beetle. As a result, more striped flea beetles survive each year and their numbers are increasing in all areas. Soroka is quick to point out that this is not to imply that the striped flea beetle has acquired resistance to neonics. In fact, there is no evidence that there has been any genetic shift in either species.

John Gavloski, provincial entomologist with Manitoba Agriculture Food and Rural Development, agrees. However, he says that changes in management practices of growers could also be contributing to higher levels of flea beetle damage.

Gavloski says that seed treatments only provide protection for about three to four weeks. Under good growing conditions, this usually provides enough time for the plant to grow large enough so that any damage done by flea beetles would not have a significant impact on crop yield.

However, many growers are now seeding earlier and into cooler soils, says Gavloski. This slows both germination and plant growth, so the seed treatment no longer provides optimum protection. This problem is exacerbated if the plants are set back by a late spring frost, as happened in 2015.

Second, growers have been lulled into complacency by the effectiveness of seed treatments and many fail to regularly scout for flea beetles, he adds. Given the speed at which a flea beetle problem can intensify, failure to scout can lead to significant losses in a matter of days (24 to 72 hours according to Alberta Agriculture and Forestry).

Low seeding rates also increase the risk of crop loss to flea beetles, says Gavloski. Some growers try to save a little money by cutting seeding rates, but they should understand that flea beetle damage rises proportionally to declining plant stand numbers. Stands of less than seven plants per square foot are at increased risk of flea beetle damage.

What to watch for in 2016

Growers need to be especially vigilant this spring, says Bob Elliott, an entomologist with AAFC in Saskatoon. Flea beetle damage is primarily caused by overwintering adults, which emerge in late summer of the previous year.

Flea beetle counts in 2015 revealed very high numbers of the insect in some research trial location, reports reveal that flea beetle trap counts were five times higher in 2015 than the year before.

And striped flea beetle numbers were up the most, he says. This means that this spring, significant crop damage from flea beetles is a real possibility.

The wild card in forecasting the flea beetle risk is environmental conditions. According to Soroka, if we have a cool, wet spring, the risk of flea beetle damage could be low in spite of the high adult numbers the previous fall. If we have a warm, dry spring however, we could face a real problem this year.

As common as flea beetles are, there is still a lot we could learn including a better understanding of the population shift of flea beetle species; any existing natural enemies to control flea beetles; any biological means to control outbreaks; and better ways to predict infestations.

Alejandro Costamagna, entomologist and assistant professor at the University of Manitoba hopes to find some answers. He is entering the second year of a three-year study of the range of flea beetle species and their predators across the prairies.

Plant breeders are also working on developing a canola plant with a hairy leaf that could reduce the palatability of canola to flea beetles