It can be hard to distinguish between grasshopper species as many of them appear to look similar. And while they may look alike, only a few of them pose a threat to farmers.
A typical Prairie system of pasture, cropland and roadside vegetation, for instance, might have 30 to 40 different species, but only four or five cause significant damage to crops.
Some grasshoppers are beneficial insects that provide important sources of food for grassland birds and other animals. And there are some non-pest grasshoppers that feed mainly on weed species like Russian thistle and kochia.
Dan Johnson, an environmental science professor at the University of Lethbridge in Alberta, offered some easy tips for scouting and identifying crop pest grasshopper species during a presentation at the Manitoba Agronomists Conference last December.
It’s easy to mistake friend from foe
It can be easy to mistake crop pest grasshoppers for non-pest species like katydids or slant-faced grasshoppers, which are often present along roadsides. As a general rule of thumb, any grasshopper that sings or chirps is not a pest. “If you can hear them, they are not a problem,” says Johnson.
Also, any grasshoppers that fly before June, or those with coloured hind wings visible during flight, aren’t pests either. And non-pest grasshoppers have distinctive genitalia on their backs that look like tiny antlers.
Meanwhile, crop pest grasshoppers usually hatch in late May or early to mid-June and three out of the four important crop pest species listed below — the two-striped, Packard’s and lesser migratory grasshoppers — have a spur on their throats.
Prairie farmers would be wise to keep an eye out for the following four main crop pest grasshopper species this season.
The two-striped grasshopper (Melanoplus bivittatus, see photo at top) is a significant and common pest that feeds on a wide range of grass, cereal and broadleaf crops including pulse crops, canola, safflower and lentils. It is a voracious eater and has been slowly increasing its range, particularly in southwest Manitoba. Two-striped grasshopper populations will typically fluctuate, going through extended periods of abundance and subsequent decline.
This grasshopper is large and has two pale stripes that run the length of its body from the eyes to the wing tips and abdomen. It also has a black stripe, which may be solid or broken, running down its back legs. The insect is generally brown to greenish-brown, but can come in various colours including green, yellow and tan.
When it first hatches, it is tiny at around three millimetres long, wingless, tan to brown in colour and covered in dots, but its legs and body clearly resemble those of an adult. As the grasshopper ages, it develops wing buds that eventually develop into wings as it grows. This is the stage when it’s best to take measures to control the insect if it is feeding on a crop.
The grasshopper typically begins feeding on weeds and grass growing at the edges of fields, so if caught during this early stage, it may not be necessary to treat the whole field but only the edges.
The Packard’s grasshopper (Melanoplus packardii) is another pest species that multiplies quickly and is common in regions with sandier soils in Alberta, with increasing numbers across Saskatchewan and Manitoba. It feeds on broadleaf crops, including pulses, and cereals, alfalfa and grass.
It is bright green as an immature grasshopper and has small dots on its back. Adults are grey to dark-yellow in colour with light-coloured stripes behind the eyes and along the thorax.
Lesser migratory grasshopper
The lesser migratory grasshopper (Melanoplus sanguinipes) is one of the most famous — or infamous — pests in Canada. Millions of these grasshoppers flew from the United States to Canada causing extensive damage to crops in the 1930s.
Lesser migratory grasshoppers, like the two-striped and Packard’s, feed on a wide range of crops, such as cereals and broadleaf crops including lentils. They can be identified by square, black dots down their sides that resemble airplane windows and sometimes they can have purplish-coloured heads.
The clear-winged grasshopper (Canmula pellucida) is a very serious pest of grasses and cereal crops, but not pulses, and is one worth looking out for, said Johnson.
It is black and white when it first hatches. Adults are yellow to brown in colour and have large brown blotches on their wings. Like two-striped grasshoppers, clear-winged grasshoppers have two stripes but they do not have a spur under their chins because they are in the band-winged subfamily and not the spur-throated subfamily of grasshoppers.
These grasshoppers congregate in large numbers when they are laying eggs. Farmers who see grasshoppers flying late in the season and which appear to be glistening in the sun are likely clear-winged grasshoppers, and it may be worth scouting for eggs, said Johnson.
Grasshopper eggs are laid in pods and can be found in the soil in clusters, against stones, posts or plant roots. Female grasshoppers back their abdomens into the ground to lay their eggs. Those eggs are held together with a biological secretion resembling foam, which forms a cover for the eggs. There are usually 30 to 50 eggs per pod. Individual eggs can look like brown rice.
“If you look at the ground, all of those long, peanut-shaped things you see are grasshopper egg pods,” said Johnson.
Two species to keep on your radar
Bruner’s spur-throated grasshopper (Melanoplus bruneri) is a species Johnson said may be a game changer in the Prairies. Their numbers have shot up in recent years and this species has wiped out some alfalfa and canola crops in Alberta and British Columbia.
In Alberta, its presence has been reported from Edmonton to the Peace River region. According to Johnson, this grasshopper was quite rare until the late 1990s when it appeared in large numbers in the Alberta Foothills.
As a result of the warm weather for the past few decades, lasting infestations can be found in west-central Alberta and interior British Columbia, and will persist with the right weather and food, said Johnson, who also predicts the species could eventually threaten crops in Manitoba and Saskatchewan, but especially regions at higher elevations or near treed areas.
Bruner’s spur-throated grasshopper looks like the lesser migratory grasshopper, but is slightly larger and darker. It feeds mainly on broadleaf plants, like forbs, and grasses. This grasshopper tends not to attack wheat and barley if there is another choice.
Another pest species to watch for is the large Carolina grasshopper (Dissosteira carolina), which is also called the black-winged grasshopper or road-duster, and can be three to five centimetres or more in length. This grasshopper has a light-yellow band on its black wings. Its dark wings also make the grasshopper highly visible when flying. This species also looks like a butterfly when it flies.
“It seems that grassland birds don’t chase it because they are fooled into deciding that they can’t catch it, or they lose sight of it when it lands due to its excellent camouflage,” said Johnson.
Carolina grasshoppers are found mainly in areas with fine-textured soils. The species will feed on pulse crops; however, its numbers are usually low.
Counting the number of grasshoppers per square metre while walking through a field can be a useful exercise for insect sampling, said Johnson. An estimate of grasshopper numbers can be determined in this way.
Start by picking out a square metre of plants about five paces ahead of you. While walking toward that area, count the number of grasshoppers that leap out of the square metre. Estimate the number of grasshoppers remaining in the area by encouraging them to jump by disturbing the grass. Repeat this exercise five times for an average number of grasshoppers in the area. However, choose a different direction to walk each time so grasshoppers do not pile up in front of you causing inaccurate results.
Sweep net sampling is another useful tool when scouting for grasshoppers. It is helpful in spring or late summer for a closer look at the grasshopper species and the stages they are at in the field, said Johnson. Walk along quickly, swinging the net in a J-stroke motion level with the top of the vegetation.
Defoliation estimates can also be carried out when scouting. Randomly select two plants in each of five areas of the field and estimate the amount of defoliation.
More details on these methods for grasshopper scouting can be found at the Province of Manitoba website.
In the past, people have used growing degree days as a rough indicator of when grasshoppers might hatch, but Johnson said that isn’t a reliable system.
“The integrated degree days is an indicator of how much heat could be used by a plant or a cold-blooded animal like an insect. If you do use degree days, you pretty well have to compute it every few days because things change. Degree days are also usually based on air temperature and that’s not where the insects are. It’s also ignoring species’ differences, timing and so on. That’s why degree-day forecasts for insects like grasshoppers are usually out by a week or two at least.”
Johnson and his colleagues have developed another model that is more predictable and recognizes different species have different growth rates depending on temperature.
“The clear-wing grasshopper needs warm conditions in order to boost its way up to successful hatching,” said Johnson. “With the two-striped, in June, we have mostly young (grasshoppers), and in late July the adults start to show up, and that’s when they have the wings.… This is not a migratory pest, so timing is not as important, but what is important is not to control too early because they are still hatching.”
For detailed information on economic thresholds, control methods as well as more grasshopper identification facts, visit the University of Lethbridge website (opens as PDF).
Provincial agriculture websites also provide detailed information on economic thresholds and control methods. For Manitoba visit gov.mb.ca, for Saskatchewan visit saskatchewan.ca and for Alberta visit alberta.ca.
Dan Johnson’s basic rules of thumb to determine if a grasshopper is a threat to your crops
Dan Johnson, an environmental science professor at the University of Lethbridge in Alberta, offers these fast-and-easy guidelines to distinguish between crop pest grasshoppers and non-pest species.
- Any grasshopper flying before June is not a pest.
- Crop pest grasshoppers hatch in late May and early June, are brown or black and always have tiny, triangular wing buds, not large wings that can be folded back when examined closely.
- Any grasshopper with hind wings highly visible in flight (red, yellow, orange or black) is not a pest. Grasshoppers have four wings — the hind wings are the flying wings, which are folded under the leathery forewings when not in use.
- Any grasshopper that sings, calls, clacks, clatters or makes other similar sounds, either in flight or on the ground, is not a pest. The pest species (and some non-pest species) are silent.
- Any grasshopper that inhabits a crop on a warm day without feeding on the vegetation may be a temporary resident that is moving to more preferred vegetation.
- Grasshoppers that remain in rangeland, headlands or other grassland without moving into crops are likely to be species that do not damage crops (monitoring during warm weather will allow this to be determined), and do not require control actions.
- Grasshoppers that appear lethargic and hang on vegetation in mid or late summer may be infected with naturally occurring pathogens that will help reduce their numbers.
For detailed information on grasshopper identification and control visit the University of Lethbridge website (opens as PDF).