Grasshoppers are relatively large insects, capable of doing considerable damage in a short amount of time. In early summer, grasshoppers normally feed on grasses and weeds in non-crop areas, and move into fields later in the season. In general, damage to crops is most severe in dry years.
Corn, soybeans, small grains and other crops may have localized problems with this pest when grasshopper populations are high. Grasshopper nymphs can consume entire soybean seedlings. On more mature plants, the nymphs eat irregular holes in the leaf issue. Adult grasshoppers consume entire leaves, except the tougher veins, and also feed on the pods.
Grasshopper populations are strongly influenced by climate
Outbreaks of this pest are more likely after two or more years of dry weather. Long, warm autumns, followed by warm, dry springs contribute to the building of grasshopper populations. A long, warm autumn favors egg-laying by grasshoppers.
The most widely distributed and economically important grasshopper species in the North Central region are
- Differential grasshopper, Melanoplus differentialis. This grasshopper favors cultivated land and can be a severe pest of small grains, corn, alfalfa, soybeans, some vegetables, and fruit trees.
- Twostriped grasshopper, Melanoplus bivittatus. This species feeds on a mixed diet of many kinds of plants and can be a major pest on small grains, alfalfa, and corn.
- Migratory grasshopper, Melanoplus sanguinipes. This species has a very broad distribution and causes more damage to field crops, gardens, and rangeland than any other species of grasshopper in North America. Small grains are particularly vulnerable. Migratory grasshoppers feed on foliage, fruit, and bark.
- Red-Legged grasshopper, Melanoplus femurrubrum can be a crop pest in alfalfa, clover, soybeans, corn, and small grains. Large numbers can develop in pastures.
- The clearwinged grasshopper, Camnula pellucida, prefers grasses and small grains.
Large numbers of grasshopper nymphs can develop in tall weedy areas, attracting little attention. However, when they become winged adults, they can fly greater distances and suddenly appear in crop fields.
Nymphs may consume the entire soybean seedling. On more mature plants, both nymphs and adult grasshoppers eat irregular holes in the leaves. Adult grasshoppers will also feed on pods.
Reductions in yield can occur during any crop stage although the pod-forming and pod-filling stages are at greater risk than other plant stages. A 40 percent leaf loss during any vegetative stage will result in only a 3 to 7 percent yield reduction. Defoliation of 20 percent during the pod-forming and filling stages will result in similar yield reductions.
There are three stages in the grasshopper life cycle — the egg, nymph, and adult. The female lays the eggs in the soil and surrounds the eggs with a frothy liquid that hardens to form a protective structure or “pod”. Typically, a female grasshopper will lay about 100 eggs during the summer and fall. Egg pods are deposited in the upper few inches of soil in grassy areas of uncultivated land such as roadsides, field margins, and pastures. A long, warm autumn favors better nutrition and increased egg-laying by grasshoppers.
Winter is spent in the egg stage. Hatching time is influenced by temperature, with earlier hatching occurring after a warm spring.
Tiny grasshopper nymphs hatch from eggs in the spring and early summer. The egg hatch for a single species may extend over a month or more. Nymphs resemble wingless adults and develop (molt) through five or six stages (instars). After each instar, they shed their cuticle (skin) and grow larger. Nymphs must start feeding within one day after egg hatch and usually feed on the same plants as the adult.
Because of limited fat reserves, young nymphs are vulnerable to adverse weather just after hatching. Young nymphs are quite susceptible to weather and natural enemies. Cool, wet conditions during egg hatch reduce grasshopper numbers. Grasshopper nymphs normally reach the adult stage in five to six weeks.
Adult grasshoppers, the only stage to have wings, readily move out of hatching areas and begin egg-laying one to two weeks after becoming adults. Adults live two to three months, depending on the weather. All developmental stages are influenced by temperature, and grasshopper growth can be advanced or retarded by favorable or unfavorable temperatures.
Most grasshopper species produce one generation per year.
Adults of the differential grasshopper, Melanoplus differentalis, are are 1 1/8 to 1 3/4 inches long. The grasshopper’s upper surface is dark brown to olive green, the under surface is yellow. It has clear, glossy hindwings. The chevron-like black stripes on the large portion (femur) of the hind legs are very distinct.
Scout for grasshoppers from July to September. Weather is the main factor affecting grasshopper populations. Watch for outbreaks in a year following several years of hot, dry summers and warm autumns. Warm autumns allow grasshoppers more time to feed and lay eggs. Dry weather increases nymph and adult survival.
Scout near grassy areas
Differential grasshoppers move in from weedy borders, so check border rows near weedy or grassy areas first. Alfalfa and clover fields are particularly favored; eggs are often deposited on field margins.
Leaf injury from grasshopper nymphs look similar to the small holes caused by Japanese beetle feeding, but are more jagged in shape. Older nymphs and adult grasshoppers will eat the entire leaf, leaving only the major leaf veins.
However, soybeans can tolerate a fair amount of defoliation. Typically, 20-25 percent defoliation of all the leaves of the plant would be necessary to justify an insecticide application in late season, pod-setting soybeans.
The differential grasshopper has a wide host range throughout North America, particularly in areas of cropland between the Rocky Mountains and the Mississippi River. Populations east and west of these landmarks are more spotty and discontinuous.
The red-legged, migratory, and two-striped grasshopper are very widely distributed, ranging over most of North America.
Different species of grasshopper develop at different rates. In Minnesota, the earliest species (the two-striped grasshopper) begins to hatch in late April to early May with other species beginning to hatch out at approximately 3-4 week intervals (Figure 1). This means that young grasshoppers of different species are going to be present throughout most of the summer.
Effect of climate and weather
Normal levels of rainfall are important to control grasshopper populations. If soil moisture content is high, many of the eggs will not hatch. Dry springs favor grasshopper populations, which is why grasshopper outbreaks generally occur during dry years.
Grasshoppers have many natural enemies
Natural enemies are the reason why we generally see only localized outbreaks of grasshoppers. Many natural enemies are specialists on grasshopper-type insects, while others are generalists, using grasshoppers as one of many hosts.
Many beneficial insects feed on grasshoppers. These include the larvae of blister beetles and ground beetles (which feed on the eggs), bee flies (parasites of eggs), robber flies, Scelionid wasps, flesh flies (Sarcophaga) and tangle-veined flies. The parasitic flies deposit eggs on the nymph or adult, and the emerging larvae eat their way into the body of the grasshopper. Generally, parasitized grasshoppers die earlier and do not reproduce.
A fungus, Entomophthora grylli, often causes locally high mortality in grasshopper populations. Once infected, grasshoppers can be seen in a characteristic pose at the top of a plant, in which the grasshopper grasps the plant in a “death embrace” with front and middle legs while the hind legs are extended. It dies in this position. Fungal spores develop in and on the body of the infected grasshopper. These spores become airborne and infect other grasshoppers. Under warm, humid conditions, great numbers of grasshoppers are destroyed by this fungus.
The red locust mite, Trombidium locustarum, is an important natural enemy that feeds on the eggs, nymphs, and adults. The mite uses its mouthparts to suck up the fluid from its host. A mite-infested grasshopper moves slowly, eats little, and dies early.
Several types of parasitic nematodes, such as the horsehair worm, are notable natural enemies of grasshoppers. Infested grasshoppers rarely produce young, and die early of dessication.
Finally, predation of nymphs and adults by larger animals such as toads, snakes, birds, skunks, shrews and moles have an impact on grasshopper populations during the summer months.
Grasshopper populations can be reduced by eliminating potential egg-laying sites. Since grasshoppers tend to select undisturbed areas for egg-laying, tilling these sites in mid- to late summer discourages females from laying eggs in these areas.
Eliminate tall grass and weeds around crops, trees and gardens you want to protect. This reduces food sources so grasshoppers are not attracted to these areas, exposes grasshoppers to greater predation from birds and mammals, and also makes these areas less attractive for egg-laying.
Similarly, summer weed control in fallow fields eliminates food sources so there will be nothing for small nymphs to feed on when eggs hatch, and fields will not be attractive to egg-laying adults.
Chemical control and biological control products
Adult grasshoppers are difficult to control with insecticides due to their size, mobility, and decreased susceptibility to the insecticides. The best time to control grasshoppers with insecticides is during the 3rd and 4th instars when they are 1/2 to 3/4 inch long. These stages will occur in early to mid-summer, depending on the species and area of the region. At this time most eggs will have hatched and the nymphs will be more susceptible to insecticides. Also, they will still be concentrated in their hatching areas where they can be controlled more effectively than when dispersed later in the summer.
The biological control agent, Nosema locustae, is a naturally-occurring microsporidian protozoan that is now being placed on various baits and marketed for grasshopper control under such names as NOLO Bait, Grasshopper Attack, Hopper Stopper and others. Grasshoppers must eat the Nosema-treated bait as second or third instar hoppers. This requires both early season scouting and treatment of grasshopper populations in border areas of the field. Flaky wheat bran treated with Nosema locustae is particularly recommended when control is needed near water or near threatened and/or endangered wildlife.