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The flea beetle is a common pest for farmers and gardeners alike in this corner of the province. However, there is more to the species than meets the eye. Provincial Insect and Vertebrate Pest Management Specialist for the Ministry of Agriculture, Dr. James Tansey, says that the term “flea beetle” covers approximately 5,000 species worldwide, in a subfamily called the Alticinae.
“They're going to be the same family as Colorado Potato Beetle and some other notorious pests. But the giveaway on flea beetles or the members of the Alticinae is great big honking hind femurs that allow them to jump great distances for their size. I'm sure people have either tried to squish them or capture them and notice that they'll just boing away in random directions.”
Of these thousands of species, two are particularly relevant here in Saskatchewan, the crucifer flea beetle and the Aphthona flea beetles. However, both play very different roles and are received very differently by local growers.
From canola fields garden beds: The life of a crucifer flea beetle
Crucifer flea beetles are primarily pests to plants in the crucifer family. This includes cabbage, kale, and broccoli. They are also significant canola pests which, explains Tansey, is why the southeast sees so many of them at this time of year.
Crucifer flea beetles have one generation per year, and the current generation are adults that are preparing to overwinter. They will appear again in the spring and begin feeding on seedling plants.
“These can be very damaging to seedling canola. They will continue to feed on these seedling plants and while they're doing this, they're beginning to lay eggs. As the plants mature, they lay more eggs. The larvae will tunnel into the soil and they'll start feeding on the root hairs and as they get larger, they'll start feeding on the roots.”
Since the beetles are underground, they can be very difficult to monitor, according to Tansey. However, they can be very numerous with up to one thousand per square metre. While underground they complete development and emerge in mid-July in large numbers depending on heat.
“We've had some heat accumulate. They're starting to emerge in large numbers. The canola is being harvested, and they don't have any host plants left in there, so, they're taking wing and they're pretty good flyers. They can fly pretty considerable distances, especially given their size, and they're looking for other members of the crucifer family.”
Tansey notes this is how they end up in people's gardens, attracted to the enzymes released by plants in the same family. Alongside their talent for flying, they are also aided by excellent vision and an excellent sense of smell.
It’s not just one beetle alone that can decimate a garden though. Tansey says their large population homing in on those specific plants allows them to inflict large amounts of damage, and they also release enzymes while interacting with those plants to attract more flea beetles.
When it comes to managing these pests, Tansey explains that associational resistance can sometimes be effective.
“You can plant your desired plant next to a plant that the that the insects find repellent. So there's some evidence that marigolds can be repellent to these animals. There's some evidence that wormwood can be repellent to these animals. Hard data on wormwood I have yet to see, though. But I have seen some data on repellents associated with marigold.”
However, being too late now to add these plants to a garden layout, he says many garners may have to resort to insecticides.
“These animals will respond to most of the insecticides that are available at a garden center. Be aware of the label recommendations associated with each, the label is the law associated with these products, even including domestic products.”
“Keep in mind, too, though, that they are very numerous at this time of year. So even with the application of an insecticide, you could still see a lot more flea beetles around.”
Representing the majority: The intentional invasion of leafy spurge flea beetles
The damage and inconvenience brought on by the crucifer flea beetle is an anomaly among the species, as Tansey explains that the vast majority are not pests. In fact, a different variation of the insect was intentionally introduced to the ecosystem to defend local crops.
Aphthona flea beetles were released in the province several years ago as a biological control program for leafy spurge.
“Leafy spurge, as many people are familiar with, is a perennial weed that is really, really problematic. It's a very deep-rooted plant and can be quite toxic and difficult to eradicate once it does become established.”
Just as crucifer flea beetle larvae feed on the roots of crucifer plants, Aphthona flea beetle larvae do the same to the stubborn weed. This root feeding causes the most damage to leafy spurge and greatly reduces the number of plants.
“One really curious thing about these particular animals is they really like each other's company. So they produce an aggregation pheromone that keeps them concentrated in a specific area, really concentrating on one small spot of the leafy spurge.”
“Year one, you might see a small hole on the spurge, year two, it'll get larger, and so on. They can really do a number on the leafy spurge establishment.”
Since this particular species of flea beetle doesn’t originate in the province, they were intentionally introduced to control leafy spurge populations. However, Tansey says vast amounts of research was done to ensure the reach of plants they impact outside of leafy spurge is minimal.
“You don't want to be introducing a pest by accident or something that's going to consume native plants. They determined that there were about five beetles in the genus that would only feed on leafy spurge and cypress spurge, and graveyard spurge in some cases and based on that, they were chosen for introduction to North America.”
They were released based on their specific needs and microclimates and have become established. From there they can be redistributed to expand their reach.