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February 2006
Manitoba Agriculture, Food and Rural Initiatives
Although there are numerous species of grasshoppers in Manitoba, there are 4 species that, given the right conditions, can cause significant damage to crops. These are the migratory grasshopper (Melanoplus sanguinipes), twostriped grasshopper (Melanoplus bivittatus), clearwinged grasshopper (Camnula pellucida), and Packard grasshopper (Melanoplus packardii). There are several steps that farmers and agronomists can take to try to minimize crop damage from these grasshoppers. Careful observations the previous fall and in late spring / early summer are important in minimizing damage and the cost of grasshopper control. Weather conditions can also influence the population of grasshoppers, and how much damage they do to the crop.
How Does Weather Affect Grasshopper Populations?
The number of grasshoppers hatching in the spring will be affected by the weather the previous summer and fall. Warm and dry summer and fall conditions will mean that there has been more opportunity for grasshoppers to lay their maximum amount of eggs. As well, there is some embryonic development that will occur in the egg before the colder weather sets in. Warmer conditions will mean that the embryonic development is further along before development ceases for the winter. The further along the development is going into winter, the earlier the eggs will hatch the next year. Earlier hatch means grasshoppers that are feeding on younger, less tolerant crops.
Warm and dry spring and summer days favor early and rapid grasshopper development. As well as affecting their ability to cause more harm to crops, this also means they will become adults and start laying eggs for the previous year sooner. So it is easy to see how several years of hot, dry conditions can build a grasshopper population up to outbreak levels.
A common question over the winter will be “what affect will cold weather have on the overwintering grasshoppers”? This depends on how cold the soil temperature is at about 5 cm below surface level. This will be affected by the amount of snow cover. Studies by Agriculture Canada scientists have determined that temperatures of -15ºC or less at about 5 cm below the soil surface are required for substantial mortality of grasshopper eggs. So if the winter wheat in the area has survived the winter well, grasshopper eggs likely have too. Also consider that grasshopper eggs are often laid in areas where snowfall tends to accumulate.
Know the egg bed areas where grasshoppers congregated the previous fall.
The species of grasshoppers that are considered crop pests overwinter as eggs, although some non-economic species overwinter as nymphs (young grasshoppers). Most of the eggs are normally deposited in a variety of non-crop areas including ditches, fencerows, shelterbelts and weedy areas. Eggs will also be laid in some late-season crops, weedy fields, headlands, pastures and alfalfa. These areas will be where egg pods are concentrated and the majority of grasshoppers will hatch the following spring. Observing where grasshoppers are congregating and laying eggs in the fall will help in determining where monitoring the next season should be concentrated.
Late spring / early summer monitoring is critical
Starting in late-May, monitor roadsides, field edges, and areas where grasshoppers clustered in late summer to lay eggs. Walking in these areas and looking carefully for grasshopper activity in the plant material, which should still be small, will help to determine if hatch has begun and how heavy the population is. If possible, try to monitor these areas at least once a week beginning in late May and estimate the number of grasshoppers per m2.
Why Early season control is best
1.) Grasshoppers are concentrated early in the season. Until grasshoppers become adults and have fully developed wings, they cannot fly. When populations are still young and concentrated around the field edges and roadsides, often control measures applied to just the field edges or roadside areas where they have emerged in large numbers is enough to provide control. If control is delayed too long and grasshoppers become adults, they can move into fields rapidly, potentially resulting in farmers having to spray whole fields to control grasshoppers.
2.) Many insecticides do not work well against adult grasshoppers. Insecticide labels often specify that control should be directed at young grasshoppers.
3.) It’s cheaper. For those insecticides that will provide adequate control of adult
grasshoppers, usually a much higher rate is required than if control was against the
juvenile stages. This increased rate that is required also increases the cost of controlling grasshoppers.
To sum up, scout for grasshoppers early in the season, and don’t just react to a problem once it has developed to the point where it can’t be ignored. If grasshopper populations are high early in the season, treat the grasshoppers before they become adults.
Adult Grasshopper
Does the sight of a few large grasshoppers early in the season mean trouble?
Regarding the early season appearance of large grasshoppers, there are a few species that overwinter as nymphs and emerge early in the season. So with these species you see large grasshoppers early. Not to worry though, none of these are pest species. All the grasshopper species capable of causing significant damage in Manitoba overwinter as eggs, and don’t start emerging usually until late-May.
The brown-spotted grasshopper (Psoloessa delicatula) is one of the species that overwinters as nymphs (it overwinters as 4th or 5th instar nymphs). It is an important food item for the survival of the nestlings of grassland songbirds. The specklewinged grasshopper (Arphia conspersa) overwinters as 5th instar nymphs, so this is another grasshopper that may be seen in a more advanced stage early in the seaason.
There is also a species called the club-horned grasshopper (Aeropedellus clavatus) that can confuse those keeping an eye on the grasshopper hatch. The club-horned grasshopper overwinters as an egg, but hatches more than a month earlier than pest species. The pasture grasshopper (Melanoplus confusus) is also a species that hatches very early, hatching in early spring.
Any grasshopper you see flying before the first of June is not a threat and has no relevance to the ones that are a threat.
Does Time of Seeding Affect the Risk of Grasshopper Damage?
Younger plants do not withstand grasshopper feeding as well as older, well
established plants. So the more developed the plants are when grasshoppers hatch and find their way into the field, the more tolerant they will be to the feeding. Good growing conditions will also help make the plants more tolerant to grasshopper feeding. Crops that are seeded late and stressed because of poor growing conditions are at higher risk of economical damage by grasshoppers. Also, early-seeded crops mature early, and migrating grasshoppers are less likely to be attracted to them as they are to lush young foliage.
Tillage and Grasshopper Control
Tillage manages grasshopper populations primarily by eliminating the green plants on which grasshoppers feed. Tillage is of little value if used for the sole purpose of physically destroying grasshopper eggs or exposing them to desiccation or predation. Excessive tillage is harmful in that it will reduce soil moisture levels and increase the risk of soil erosion.
Overgrazing can increase grasshopper problems
Overgrazing promotes grasshopper abundance because open patches of bare or sparsely-covered ground make excellent egg-laying sites for many of the troublesome species. Also, plant composition on overgrazed rangeland promotes grasshopper survival and egg production of those same species.
Will burning grasslands help control grasshoppers?
Burning grasslands in the fall is reported to have no effect on grasshopper eggs. Burning may even benefit grasshoppers by providing the small nymphs which hatch in the spring with easier access to sunshine and warmth on cooler days and by inhibiting the development of protozoan and fungal diseases of grasshoppers.
Natural Enemies of Grasshoppers
Next to weather, natural enemies are the most important factors controlling grasshopper populations. In some localized areas, natural enemies may even be a more important factor than the weather.
Egg Predators: Among the most important predators of grasshopper eggs are bee flies, blister beetles, ground beetles, and crickets. Some species of bee flies and blister beetles will deposit their eggs in the soil near grasshopper eggs, which enables the larvae to easily find grasshopper eggs to consume. When bee flies and blister beetles are abundant, they may destroy up to 80% of the grasshopper eggs in a localized area.
Nymph and Adult Predators: Spiders, robber flies, some wasps and many birds may feed on grasshoppers and consume them in large numbers. The effect of these predators on the total grasshopper population is not fully known.
Parasites of Grasshoppers: Grasshopper eggs are sometimes parasitized by the wasp Scelio calopteni. Grasshopper nymphs and adults are sometimes parasitized by sarcophagid and tachinid flies. As well, horsehair worms (which are long, whitish and extremely slender) sometimes parasitize grasshoppers. The eggs of this parasite are ingested by crickets and grasshoppers. After hatching, the worm penetrates the grasshopper’s body cavity and grows in length. When the weakened host falls into water, the worm exits and swims away.
Diseases: A fungal disease, Entomophagus grylli, occurs naturally in the Canadian prairies, infecting grasshoppers, especially during seasons when the humidity is high. Infected grasshoppers typically climb to the top of stems and wrap their legs around them and then die. The body is filled with fungal spores. As it disintegrates, the sticky spores transfer to other grasshoppers, killing them.
A protozoan, Nosema locustae, can infect grasshoppers if the grasshoppers ingest
infected vegetation or an already diseased grasshopper. A grasshopper population
infected with this organism may be reduced from 5 to 40% in one year. N.
locustae can reduce feeding rates to as low as one-third of normal. This parasite
also appears to affect grasshopper populations by reducing the number of eggs
laid.
Resources for Identifying Grasshoppers
The website http://www.sidney.ars.usda.gov/grasshopper/index.htm provides good information on grasshopper biology, identification and management. Once on this website, the link “Grasshopper Identification Tools and Species Fact Sheets” will provide a list of sites that are helpful for grasshopper identification.