Background
Grasshoppers are a major pest of both cultivated crops and rangeland grasses in the world's semi-arid regions. Areas receiving less than 750 mm of precipitation in the form of rain or snow are particularly susceptible. Traditionally drier areas like southern Alberta are more prone to recurring problems, but serious grasshopper infestations can occur in cropland throughout the province.
Although the majority of grasshopper damage has been to cereal grains, other crops can be seriously affected. In a more diversified agricultural landscape where cereal crops are often rotated with other crops such as canola, lentil and peas, grasshoppers continue to cause significant economic loss in Alberta. Grasshoppers eat 30 to 100 mg of plant material (dry weight) each day.
Forage losses are seldom estimated, but it has been shown that even a moderate infestation of 10 grasshoppers/square metre can typically consume up to 60% of the available forage, depending on the condition of the forage stand. The insects can also consume all of the cereal crops, but they usually work the outer edges of fields.
The type and extent of crop damage will depend on the type of crop, how well the crop is growing, the number of grasshoppers present, and whether or not adequate cultural and chemical controls are used.
For current and past Alberta surveys and survey findings, see Grasshopper forecast and maps.
Description
The name ‘grasshopper’ has been given to a very large and diverse group of insects. All members of the group are characterized by chewing mouth parts, slender bodies, wings that fold lengthwise, large powerful hind legs for jumping and a gradual change in form and size as they develop.
Grasshoppers are divided into 2 major subgroups:
- Short-horned grasshoppers (Figure 1)
- Long-horned grasshoppers, Mormon crickets and katydids (Figure 2)
Short-horned grasshoppers are responsible for most of the reported crop losses. As a result, individuals of this subgroup are popularly referred to as ‘grasshoppers.’
Figure 1. A mature two-striped female grasshopper (Melanoplus bivittatus). Note the distinct 2 stripes running the full length of the body and the single black stripe on the hind leg.
Figure 2. The Mormon cricket (Anabrus simplex) is an example of a long-horned grasshopper. The adult male hangs on vegetation and sings loudly. This species can reach high densities in the U.S., but does not normally cause a problem in Canada.
North America has more than 600 species of grasshoppers. In Alberta, there are more than 85 species. There are about 12 grasshopper species of economic pest importance at some times, and of these, only 5 are considered pest species.
The species that are considered pests are economically important because under ideal food and weather conditions, these grasshoppers multiply quickly, and when present in large numbers, they feed excessively.
When discussing grasshoppers, it is also important to note that the insects play a significantly positive role in the cycling of nutrients in natural ecosystems since they are food for birds and other animals. In many cases, grasshopper control is not required if they are merely present and are not reaching economic damage thresholds.
Significant species
The short-horned grasshoppers are divided into 3 types:
- Spur-throated
- Band-winged
- Slant-faced (do not generally need control measures)
Each type has distinguishing characteristics that make them relatively easy to identify. Producers need to recognize these characteristics if they are to control grasshoppers effectively.
1. Spur-throated grasshoppers
Includes pests in the genus Melanoplus.
These grasshoppers are identified by the presence of a tubercle or knob between their front legs (Figure 3). Three of the most economically important species are members of this group: the migratory, Packard’s and the two-striped.
Figure 3. Spur-throated grasshoppers all possess a spur-like structure on their underside, just between where the front legs are attached.
Migratory grasshopper
The migratory grasshopper (Melanoplus sanguinipes) is a very successful species. It is adapted to every ecoregion of the Canadian grasslands and exhibits remarkable variability in colour and physical proportions, such as length of the wings. Of all the species within the genus Melanoplus, M. sanguinipes, is the most widely distributed, occurring as far south as Florida.
Figure 4. A migratory grasshopper (Melanoplus sanguinipes). This pest grasshopper can be recognized by the dark bands just behind the eyes.
Find out about the characteristics and life cycle of the Migratory grasshopper.
Packard’s grasshopper
The Packard’s grasshopper (M. packardii) (Figure 5) typically occurs throughout the prairies, preferring loose sandy soils. There is some colour variability in this species within Alberta, with southern specimens being generally paler. This species is less common than two-striped grasshopper and is a more moderate threat. Population numbers can increase in areas with sandy soils and dry conditions.
Figure 5. An adult Packard’s grasshopper (Melanoplus packardii) settling in on an alfalfa plant. Most grasshoppers can eat from 30 to 100 mg of dry weight material per day.
Find out about the characteristics and life cycle of the Packard’s grasshopper.
Two-striped grasshopper
The two-striped grasshopper (Melanoplus bivittatus) is widespread throughout Canada and common throughout Alberta. It has the heaviest body weight of the three spur-throated grasshoppers discussed here. It rarely flies far, but can walk well into a crop as it feeds.
Figure 6. An adult two-striped grasshopper. Note the black stripe on the hind leg as well as the 2 distinct stripes on top of the body running the full length of the grasshopper.
Find out about the characteristics and life cycle of the Two-striped grasshopper.
2. Band-winged grasshoppers
The main characteristic of band-winged grasshoppers is that the hind wings are usually brightly coloured (Figure 7(a), (b). While in flight, these grasshoppers may produce a cracking sound with their wings. The Carolina grasshopper with its black wings fringed with a pale border is probably the most noticed member of the group (Figure 8). The most economically important species is the clear-winged grasshopper.
Figure 7a. The coloured wings on these 2 band-winged grasshoppers are a clear sign that these are not pest species. The clear-winged grasshopper is in the band-winged grasshopper family and is a pest species. However, and as the name implies, the clear-winged grasshopper has clear wings.
Figure 7b. As above.
Figure 8. The Carolina grasshopper (Dissosteira Carolina) is a band-winged grasshopper. This grasshopper is quite common and is easily recognized by its large black wings with a pale-yellow stripe. This grasshopper could become more of a pest concern on the prairies.
Clear-winged grasshopper
The clear-winged grasshopper (Camnula pellucida) (Figure 9) can be found throughout Alberta; however, this grasshopper exhibits extreme fluctuations in abundance from year to year.
Figure 9. A mature clear-winged grasshopper female.
Figure 10. Clear-winged grasshoppers feeding on wheat.
Find out about the characteristics and life cycle of the Clear-winged grasshopper.
3. Slant-faced grasshoppers
Slant-faced (also known as tooth-legged) grasshoppers are not as abundant as the other types of grasshoppers. This group often goes unnoticed by the casual observer, and does not generally warrant control measures.
Slant-faced grasshoppers are characterized by a slanting to nearly horizontal face, their clear hind wings, conspicuous sword-shaped or occasionally club-like antennae and broadly rounded thorax. An example of a typical member of this group is shown in Figure 11.
Figure 11. The velvet-striped grasshopper (Eritettix simplex tricarinatus) is a slant-faced grasshopper. Note the spines on the back legs that are used for ‘singing.’
The slant-faced grasshoppers are usually found along the borders of marshes and in wet meadows. However, some members of this group are also common in dry, grassy fields and pastures. The slant-faced grasshoppers feed primarily on rangeland grasses and sedges. They are seldom associated with cultivated crops. Slant-faced grasshoppers have ‘teeth’ or spines that are used for ‘singing.’
Life cycle
The life cycle for all ‘economically important’ grasshoppers in Alberta is essentially the same. During the 2 weeks following mating, the female grasshopper hunts for an appropriate site to deposit her eggs. Once she selects a site, she bores a hole into the soil with her abdomen and deposits a cluster of cream to orange coloured, slightly bent, cylindrical eggs. She then deposits a foamy secretion over them. This secretion hardens to form an egg pod.
The number of eggs per pod varies greatly, ranging from 8 to one hundred and fifty. As a rule, grasshopper species that deposit few eggs per pod produce more pods than those that have many eggs per pod. Under optimum environmental conditions, a single female grasshopper may produce an egg pod every 2 to 4 days. Consequently, an average female grasshopper has the capacity, under ideal conditions, to produce more than 250 eggs in her lifetime, although this full potential is rarely achieved in nature.
Embryological development begins once the eggs are laid and continues until environmental conditions become unfavourable in the fall. Development resumes in the spring as the soil temperature rises. A temperature of 10oC is considered to be the minimum temperature at which embryo development will continue.
Hatching of the pest grasshopper species begins between early May and mid-June. Newly hatched grasshoppers, or nymphs, are approximately 5 mm (0.2 of an inch) in length. In appearance, these nymphs resemble adult grasshoppers, except for their size and the absence of wings. After hatching, the young grasshoppers begin feeding almost immediately on the surrounding plants. Although they are preferential feeders if choices are available, the insects cannot travel great distances at this stage and will consume most green vegetation close to the hatching sites.
Nymphal development consists of growth interrupted by periodic skin shedding (moults). When food is abundant and the weather is warm but not too wet, it will take 35 to 50 days for the nymphs to go through the (five occasionally six) nymphal stages before becoming a winged adult. Generally, the adult females are slightly larger than the males.
Annual cycle
Although the life cycle of all grasshopper species is somewhat similar, the annual cycle may vary considerably. Variation between species depends on when the cycle begins and how long it lasts.
Some grasshopper species overwinter as nearly full-grown hoppers and are out the following spring in March and April. All of the pest grasshopper species in Alberta begin their annual cycle in late summer or early fall of the preceding year and overwinter as eggs. These species start to hatch in early May and because of their small size at this time, are easily distinguished from the species that overwinter as larger nymphs.
In Alberta, no grasshopper species has more than one generation per year.
Control
At high numbers, any type of grasshopper is considered a regulated pest in Alberta. Assess the damage present; if it needs control to prevent economic loss and the loss is greater than the cost of the control, then control should be taken. Next to weather, natural enemies are the grasshopper's most important population control factor. In some localized areas natural enemies may cause even more mortality than the weather.
Find out about best management practices for grasshopper control, including weather effects, natural enemies, and cultural and chemical control methods.
Economic thresholds
The economic threshold or density of a pest at which control measures become economically viable has been established in most cereal crops. The economic threshold depends on several factors:
- stage of the insect
- type of crop
- crop stage
- growing conditions
- cost of control
- current market value of the crop
The most serious economic damage due to grasshoppers happens while the insects are in the third to fifth nymphal stages.
Since there are a number of factors to consider, the economic threshold in each situation can vary. Considering the above factors, the economic threshold in cereal crops ranges from 8 to 12 grasshoppers per square metre.
Table 1. Economic thresholds for grasshoppers
| Number of grasshoppers/m2 | ||
|---|---|---|
| Field | Roadside | |
| Control not usually required | 0 - 6 | 0 - 12 |
| Control may be required | 7 - 12 | 13 - 24 |
| Control required | 13+ | 25+ |
Oats and peas as guard strips
Feeding preference studies have shown that oats is an exception in that it is not a preferred food source for grasshoppers. If choices are available, the grasshoppers will ignore oats in favour of a more desirable food source. Peas are another example of a non-preferred crop. In both these cases, even if grasshoppers do feed on the crop, damage is more limited, and their biotic or reproductive potential is reduced. Therefore, these crops can be used as a guard strip around preferred crop.
This strategy is a reverse of the trap strips previously considered. In this case, the grasshoppers will tend to look for other food options rather than penetrate the guard strip into the main crop.
Lentil
Lentil has been shown to be more susceptible to grasshopper feeding than other crops. Grasshoppers are partial to developing lentil pods above the canopy. The insects will even part the flower parts to consume the early minute pods.
Yield losses result if entire pods are consumed, but even moderate feeding on the pods will break the integrity of the pod, resulting in premature shattering and subsequent yield loss. If the feeding on the pod is less severe but still results in holes in the pod, the risks of disease and staining of the seeds, which will result in a grade loss, are increased. Because of these factors, the economic threshold in lentil is considered to be only 2 grasshoppers per square metre.
Canola
Canola is not a preferred crop for some species of grasshoppers; however, grasshoppers will still feed on the crop. Canola can be damaged when it is very young and again when the pods are ripening, but it is fairly safe in between. However, significant damage can occur at all stages of growth when grasshopper pressure is high.
Early observations suggest that B. napus canola varieties have more trouble recovering from grasshopper feeding than do B. rapa varieties. B. juncea varieties appear to recover best out of the three.
Field experiments conducted at the Lethbridge Research Centre to investigate grasshopper damage just before harvest demonstrated that both the migratory and the two-striped grasshopper caused significant pod and seed damage.
The migratory grasshopper damaged pods primarily by chewing holes in the pods, and the two-striped grasshopper generally removed whole strips from the sides of pods. Both grasshopper species reduced yield enough to justify an insecticide application. The two-striped grasshopper consistently reduced profits in canola more than the migratory grasshopper.
An economic threshold of 7 to 12 grasshoppers per square metre is recommended for canola.
For more information
See economic thresholds for insects attacking: