Predicting future grasshopper outbreaks by rewinding the clock

By Tim Kalinowski


For as long as human agriculture has existed the threat of grasshoppers has hung over it. Adding to the almost biblical dread associated with the creatures is the fact they seem to rise out of nowhere, descend like a plague for a few months or a few years, and then as quick as they appear they are gone again.

Fortunately modern agriculture is getting better at tracking the vectors for infestation for these voracious creatures, and better at predicting an outbreak.

On top of this, our body of knowledge about these insects has grown immensely in western Canada, and much of that success can be credited to Dr. Dan Johnson, a professor at the University of Lethbridge specializing in insects, and former president of the Entomological Society of Canada.

Johnson has been cataloguing and tracking various species of insects for a number of years, but admits he has always had a particular fascination for grasshoppers.

“This is a group of insects which is diverse,” Johnson says. “In Alberta, there is about 100 species, and it is a big part of ecosystems as well as being an agricultural pest. It is actually a huge benefit for wildlife food webs. So it has both positives and negatives, and it is very complex.”

Over the last number of years, Johnson has been spearheading the collection of data on historical grasshopper numbers and species counts in the province from over 73,000 sites. He and his students  have also compiled over 100 years of grasshopper data, and are in the process of creating computer models based on this data which may be able to predict future outbreaks, and may even be able to predict the areas of the province where those are likely to occur.

“That is an interesting database if you can actually get some precision out of it, and some accuracy,” Johnson says. “And then, say, compare that to changing weather patterns, changing land use, and so on.

“I wanted to look at the longterm fluctuations. The way these species ebb and flow, and change their distribution, is really turning out to be something interesting—this feeling that grasshoppers are all the same, and they all react to weather the same way and so on, is absolutely not true.”

Early computer modelling suggests, like the proverbial canary in the coal mine, there are specific areas of Alberta which tend to get hit by an approaching outbreak first, sometimes as much as a year in advance, says Johnson.

“At the beginning of any increase, there is always little spots ahead of the others,” he confirms. “So one farmer might experience one of those little 50-mile wide areas where they are coming up early. There is a spot near Claresholm where this happens, Granum, and there is a few spots around there where that happens. Another is Oyen, Acadia Valley— they are often just a year ahead of everybody else.”
Johnson says he doesn’t really know why this occurs, but one of his grad students has even been able to get a bit deeper into the data to look at specific farms in these areas which tend to get hit the hardest early on.
“We picked out spots like that where outbreaks tend to persist,” he explains. “We have used computer modelling which shows if they go into an outbreak, how long they stay in an outbreak. And when they are not in an outbreak, how long they stay out of an outbreak. You can make a probability map which shows what I like to call, ‘the unluckiest farm in all of Alberta.’
“There is always someplace which is really red (on that map), and those are the spots where outbreaks really last a long time when they come.”
Johnson says the data also reveals much of what his eye in the field has been telling him for decades: Only certain species of grasshopper, perhaps ten, are a threat to traditional agriculture. And of those ten, only four species have charted massive outbreaks in the last 40 years.
“When they explode like that, it is generally just two or three species that do it,” he confirms. “There are just so many species that just never reach outbreak proportions like that because they don’t lay enough eggs. They don’t react to vegetation and weather quite as quickly as the pest species.”
Of the four most likely suspects, three converged in the most widespread outbreak in modern history, which took place in 1985-86: The Migratory grasshopper, Two-striped grasshopper and Packard’s grasshopper.  From an entomological perspective, that was an interesting year, says Johnson, with numbers 400 per cent above normal.
“Man, what a year,” remembers Johnson with awe. “In 1985-86 there were cars sliding off the highways in places on all the grasshoppers. It was that bad.”
But the most devastating grasshopper outbreak in Johnson’s experience took place in 2002-2003. It was not as widespread as the 1986 outbreak, but the sheer concentration of devastation was terrifying to behold, says Johnson.
“In 2002-2003 in central Alberta and east central Alberta, and west central Saskatchewan it was huge,” he remembers. “We had field after field that looked like summer fallow, nothing green at all, but it was eaten off.
“To give you an example of how bad it was,” Johnson adds; “ten for square metre is definitely an agricultural problem, and sometimes it might be 20— which is really the situation where people are reaching for the sprayer and calling in the planes. But up there around Coronation and Consort, and so on, in 2002-2003 there were places with 800 grasshoppers per square metre.”
The weird thing about this outbreak, explains Johnson, was it was all attributable to one species: The Clear-winged grasshopper. This species is usually one of those which tends to get virtually wiped out by fungus pathogens between outbreaks, but every so often it breaks out. No one is really sure of why, says Johnson, but one thing is certain— fungi is the main natural enemy of all grasshopper species, and the best friend of farmers in the throes of an outbreak.
“Grasshopper reproduction is limited by heat,” he says. “If you don’t get enough heat, you don’t get a grasshopper outbreak. But if you get two or three years of lots of heat, you can pretty well bet you will have one unless its wet, warm weather; that kind of weather actually benefits the fungus.”
Weather can also be a key ally in ensuring a probable outbreak may never become an actual one, says Johnson.
“A few years ago, there was a huge outbreak coming up in the Peace River country,” he explains by way of example. “It was going to be gigantic. Then what happened is they started to hatch, and it snowed right on them. So the first wave of hatching had no chance. So then it dried up and warmed up again, and they started hatching again. And then it rained for almost a week. So between those two things you almost couldn’t find a grasshopper in July. They were just slaughtered by the billions.”
Johnson says the problem with a weather event like that, or a wet, cold spring like southern Alberta experienced this year, is it is not just devastating for those pest species of grasshopper; it is devastating for all species of grasshopper, even the harmless ones which are crucial to sustaining rangeland and prairie ecosystems.
“Not all grasshoppers are bad,” stresses Johnson. “For example, any grasshopper with a coloured wings is not a pest. Anyone that sings or scritches or clicks are not a pest. There are rules of thumb like that are not really scientific, but they are quite handy to know when you are out on the land.
“Many of these (non-pest species) of grasshoppers that live out on rangeland are, however, really important bird food. We did a study where we looked at the diet of songbirds on grazing reserves, and 85 per cent of their diet was grasshoppers. Without the grasshoppers those baby birds just wouldn’t make it.”
And, he says, grasshopper species’ diets tend to be as diverse as the species themselves.
“Some of them are surprising,” states Johnson. “I mean there is a grasshopper that call Turnbull’s grasshopper that eats kochia, Russian thistle and goldenrod, things like that. If you confine it with wheat and barley, and I have done it, it dies.”
The key for farmers to know if they have a grasshopper problem or not, says Johnson, is intelligent monitoring.
“There are all kinds of grasshoppers out there,” he states, “and of course the ones who increase their numbers rapidly and feed on wheat, barley and even canola can be a serious problem, and they have to be controlled. But that is only done with intelligent monitoring, and I think most farmers are really on the ball on that. But the problem is between outbreaks people get busy with other things, and people forget about grasshoppers, and what those outbreaks are like. It’s worth kind of being aware, you know?
“Grasshopper numbers have been creeping up slowly these past few years,” he warns. “I do see them when I am out there in the summer. It’s not a huge jump, but a potential outbreak could happen if we had another couple of years with a nice, warm spring.”
For more information on the types of grasshoppers, and to identify which ones can be a risk to crop and livelihood, see the comprehensive guide Dr. Johnson has compiled for Alberta Agriculture by viewing it one at