Grasshoppers in vegetables
Order: Orthoptera
Family: Acrididae
Description
The redlegged grasshopper (Melanoplus femurrubrum) can be shades of red, brown, yellow, green, and olive green. These grasshoppers have a pointed spur located between the base of the forelegs and can fly up to 40 feet when disturbed. They tend to fly fast and evenly about a yard above vegetation.
The migratory grasshopper (Melanoplus sanguinipes) is a medium-sized, dark gray grasshopper with red and yellow tinges near the back and bottom of the abdomen, respectively. Hindlegs of these grasshoppers have blue-green or red tibia, and wings that extend beyond the tip of the abdomen.
The clearwinged grasshopper (Camnula pellucida) is small or medium-sized with gray brown to yellow coloration. The hindwings are clear and can be used to easily distinguish this species from other pestiferous grasshoppers in Colorado.
Melanoplus lakinus, commonly referred to as the Lakin grasshopper, is medium sized with brown and yellow markings. Often, the hindwings are short, however some individuals have longer wings that extend to the tip of the femur on the hindlegs.
The differential grasshopper (Melanoplus differentialis) and twostriped grasshopper (Melanoplus bivittatus) are relatively large in comparison with the other three species. Differential grasshoppers can be yellow, green to brown, or olive green. The hindleg femurs have a black chevron pattern. Twostriped grasshoppers are green or tan with black spines on the hind tibia. There are also two distinct yellow lines running along the length of the grasshopper’s back.
For images of each grasshopper, consult the webpage on grasshoppers in hemp.
Quick Facts
- There are over 100 grasshopper species in Colorado, but only several are considered pests.
- Grasshoppers can feed on a wide range of plants, especially when food is scarce. Preferred vegetables include lettuce, carrots, beans, sweet corn, and onions. Grasshoppers tend to avoid squash, peas, and tomatoes (leaves, not fruit).
- Grasshoppers are difficult pests to control because they are highly mobile. During periods when local outbreaks are developing, control usually involves using perimeter sprays or baits, which tend to have limited efficacy
- All grasshoppers lay eggs in soil as pods and often consumed by larvae of blister beetles.
- Grasshoppers are closely related to crickets and katydids.
Mating pair of differential grasshoppers on an injured host. Over 100 species of grasshoppers occur in Colorado and their populations fluctuate from year to year. They may cause serious damage to vegetable gardens during outbreaks, usually associated with periods of drought. Image credit: David Cappaert, Bugwood.org
Feeding injury due to grasshoppers. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Grasshoppers on drybeans grown in field. Image credit: Howard F. Schwartz, Colorado State University, Bugwood.org
Grasshopper on pumpkin stem. Image credit: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org
Common bean injured by grasshopper feeding. Image credit: Howard F. Schwartz, Colorado State University, Bugwood.org
Common bean with severe defoliation due to grasshopper feeding. Image credit: Howard F. Schwartz, Colorado State University, Bugwood.org
Life history and habits
All grasshoppers lay their eggs in soil as tight clustered pods. Dry soils undisturbed by tillage or irrigation are preferred. The timing of egg hatch depends on soil temperature, for most species this occurs in mid to late spring. At egg hatch the tiny first stage nymphs move to the surface and seek tender foliage on which to feed. The first few days are critical to survival, and adverse weather or absence of suitable foods can cause high mortality. Surviving grasshoppers continue to develop over the next several weeks, usually molting through five or six stages, before ultimately reaching the adult form.
The most important factors in grasshopper populations are weather-related, particularly around the time of egg hatch. For example, cold, wet weather is very destructive to newly hatched grasshoppers.
Injury
Grasshoppers have chewing mouthparts and can defoliate entire plants. Food habits vary between species of grasshoppers, where some primarily feed on grasses or sedges, while others prefer broadleaved plants. Most grasshoppers prefer younger, tender foliage. They can also be significant pests of field crops and rangeland in years when their populations are extremely high. Surveys of grasshoppers can be very useful in anticipating problems and informing decisions related to management. The number of grasshoppers present in late summer and early fall can be a good indicator of problems in the subsequent year. Predicting outbreaks is complex, and the USDA ARS in Montana has excellent resources including a prediction model updated each year.
Biological control
Preserving natural enemies is an important component of integrated pest management, and there are many natural enemies of this pest. Some species of blister beetles develop on grasshopper egg pods. Adult robber flies are common predators of grasshoppers during summer and other flies develop as internal parasites of grasshoppers. Many birds, notably horned larks and kestrels, feed heavily on grasshoppers. Grasshoppers are also frequently eaten by coyotes.
In addition to predators, grasshoppers are also susceptible to certain pathogens. A fungus (Entomophthora grylli) infects grasshoppers causing them to move upwards and cling to plants shortly before they kill the insect host. Stiff, dead grasshoppers found stuck to a grass stem or twig indicate infection with this disease. Another entomopathogenic fungus, Beauveria bassiana, is commercially available and marketed for grasshopper control. A nematode (Mermis nigriscens) also occasionally attacks and develops in grasshoppers. Both the fungus disease and nematode parasite are favored by moisture. Lastly, Nosema locustae (Canning) is a commercially available protozoan that can infect grasshoppers through baiting, however there are certain criteria that will increase the efficacy of N. locustae. Only young grasshoppers are susceptible, and it cannot be used effectively after adult migrations have occurred. Often it is most effectively used in a long-term grasshopper management program in combination with other controls. The baits are also perishable and are best kept refrigerated before use. More information on N. locustae can be found in the Utah State University factsheet. For more information on grasshopper management through baiting, see the chemical control section below.
Cultural control
In gardens and small plantings, grasshoppers can be handpicked and squashed. One strategy that can mitigate grasshopper densities during migrations is to keep an attractive green border of tall grass or lush green plants around the perimeter of the garden. This will trap the insects and divert them from vegetables or flowers.
Chemical control
Treatments should be directed at young grasshoppers and vegetation near breeding sites. This often occurs in May at lower altitudes and June at higher altitudes. Insecticide treatments do not need to completely cover the area since grasshoppers are mobile. Garden plants can also be sprayed as a last resort, but it is important to note that the grasshoppers need to feed on plants in order to acquire the toxin, which means that grasshoppers may continue feeding on plants after the insecticide application. When large numbers of grasshoppers are invading the area, repeat applications will be necessary at 3–4-day intervals.
Another protocol for chemical management of grasshoppers involves the use of baits. To be successful, baits and sprays need to be applied during developmental stages and concentrated at sites where egg laying occurs. The ability of baits to control grasshoppers declines as they develop and migrate. Alternately, certain baits can be broadcast. Bait formulations are made by mixing the insecticide with bran or another carrier and must be re-applied after rain.
References
Cranshaw, W. & R. Hammon. 2013. Grasshopper Control in Gardens and Small Acreages. Colorado State University – Extension. Available https://extension.colostate.edu/docs/pubs/insect/05536.pdf
Edwards, E. & Hodgson. E. 2008. Grasshoppers. Utah State University – Extension. Available https://extension.usu.edu/pests/research/grasshoppers
Royer, T. & E. Rebek. 2017. Grasshopper Control in Gardens and Landscapes. Oklahoma State University – Extension. Available https://extension.okstate.edu/fact-sheets/grasshopper-control-in-gardens-and-landscapes.html
Download or view the CSU Extension’s PDF fact sheet for your reference.