If the spring is hot, grasshoppers will hatch early and develop quickly. Cool spring temperatures will slow development. Crop development is also affected by less than ideal temperatures. The relationship between temperature and rainfall controls the amount of crop damaged by grasshoppers. Under hot, dry conditions, a small grasshopper population may do as much damage as a large grasshopper population will under cool, wet conditions. Moisture may also influence the size of the grasshopper population.
During an extended drought, lack of water may slow the development of many eggs and can destroy eggs, especially during certain embryonic stages and just before hatching eclosion. However, it has to be extremely dry before the grasshopper embryo begins to die under drought conditions. Rainfall may affect a localized grasshopper population to a lesser extent. Rainfall will only have an effect if a heavy downpour occurs immediately after an extensive hatch. However, a cool, wet June will not seriously affect grasshopper populations. The main effect of cool, wet weather is twofold: to reduce crop losses by hindering grasshopper development and to increase the possibility of disease in the grasshopper population, thereby helping to reduce next year's grasshopper population.
Natural enemies Next to weather, the grasshopper's natural enemies are the most important factor in controlling grasshopper populations. In some localized areas, these enemies may even be a more important factor than the weather. Some of the grasshopper's enemies attack eggs in the soil while others attach to the nymphal and adult stages of the grasshopper. Egg predators Among the most important of the egg predators are bee flies, blister beetles, ground beetles Figure 13 , crickets and other insects.
The adults of some of these insects, like the common field cricket, feed directly on the eggs and may destroy up to 50 per cent of the eggs in some areas. Other egg predators like the bee flies and blister beetles, deposit their eggs in the soil near grasshopper eggs.
When the larvae of egg predators hatch, these larvae locate the egg pods and feed directly upon the eggs. When bee flies and blister beetles are abundant, they may destroy up to 80 per cent of the eggs in a localized area. Egg parasites A few other insects, such as the wasp-like members of the genus Scelio, deposit their eggs within the newly-laid grasshopper eggs. The young complete their development within the egg and will emerge, instead of young grasshoppers, in time to parasitize the eggs of the next generation of grasshoppers.
These egg parasites may destroy from 5 to 40 per cent of the eggs, as was observed in the egg survey.
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Nymphal and adult predators Spiders Figure 14 , robber flies Figure 16 , some wasps and many birds may feed on grasshoppers and consume them in large numbers. However, the effect of these predators on the total grasshopper population is not fully known. Nymphal and adult parasites and diseases This group contains a large number of natural enemies including flesh flies, robber flies, muscoid flies, tangled vein flies, threadworms, fungi, micro-sporidians and numerous others.
Most of the fly larvae either burrow into the grasshopper when they come into contact with it on the ground, or they are deposited on or into the grasshopper's body. The fly maggot then feeds inside the grasshopper and eventually kills the host as it leaves the body. This group of insects may have a cumulative parasitism of up to 60 per cent.
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The "threadworms" overwinter in soil and lay their eggs on the soil or on vegetation. Threadworms attack grasshoppers if the young larvae encounter a grasshopper or if grasshoppers eat threadworm eggs. The fungus Entomophaga grylii can be effective in controlling grasshoppers under warm, humid conditions. This fungus may occasionally reach epidemic proportions. The disease leaves the corpses of its victims clinging to the stems of plants. The naturally occurring microsporidian parasite Nosema locustae has also been shown to have an effect on grasshopper populations.
A grasshopper becomes infected if it ingests infected vegetation or an already diseased grasshopper.
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A grasshopper population infected with this organism may be reduced from 5 to 40 per cent in one year. The parasite 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. Attempts to use this organism as a biological control agent have shown only limited success.
Since most of the natural enemies of grasshoppers are already widespread, it is unlikely that these enemies could be used to prevent grasshopper outbreaks over extensive areas. Such a strategy would only succeed if these natural enemies were cultured and distributed in larger numbers, a very expensive operation. Nevertheless, natural enemies do play an important role in controlling localized grasshopper infestations, and all are important to some extent in hastening the decline in grasshopper populations.
Cultural control methods Of all the methods available for grasshopper control, cultural control methods are generally the least expensive. These methods do not require additional or special procedures; they merely involve good management strategies and the proper timing of normal operations necessary in the production of a crop.
By modifying the grasshopper's environment at certain critical periods of its life cycle, a producer may reduce grasshopper numbers directly or can, at least, affect their ability to reproduce. Despite the advantages cultural control methods offer, many producers are reluctant to use them since it is difficult to assess their effectiveness. Nevertheless, these methods are effective if implemented well in advance of any insect attack.
These methods take time to work. Cultural control is a preventive approach to insect control. Early seeding Crops should be seeded as early as possible.
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Older plants that are growing vigorously can withstand more grasshopper feeding than younger plants, which are not well established. Although early seeding will not prevent crop damage entirely, it will reduce the amount of damage to crops and will allow more time for the producer to obtain and apply insecticides. Also, early-seeded crops mature early, and migrating grasshoppers are less likely to be attracted to them as they are to lush young foliage.
Crop rotation Whenever possible, avoid seeding cereals on stubble fields heavily infested with grasshoppers. Cereals should be seeded on stubble fields only where soil moisture is adequate and where one or more applications of an insecticide over the entire field is economical. Tillage Cultivation of the soil is a cultural practice available to producers for the reduction of grasshopper populations. Using tillage to control grasshoppers has to be considered carefully, especially under drought conditions. Tillage controls grasshoppers primarily by eliminating the green plants on which grasshoppers feed.
The practice is of little value if used for the sole purpose of physically destroying grasshopper eggs or exposing them to desiccation, predation birds and other predators. Excessive tillage is harmful in that it will reduce soil moisture levels and increase the risk of soil erosion. Fall tillage to get rid of weeds from summerfallow during late summer and early fall will discourage female grasshoppers from depositing their eggs in these fields. Grasshoppers seldom lay eggs in clean summerfallow even when it has a heavy covering of trash. Similarly, thorough field cultivation immediately after harvest will help discourage grasshoppers from laying all their eggs in the field.
It is advisable to complete early spring tillage or chemical fallow to eliminate all green growth on stubble fields before the grasshoppers have hatched. If no food is available for the young grasshoppers to eat when they hatch, they will starve. Early tillage also provides additional benefits: it gives good weed control and conserves moisture at no extra cost. Tillage can be used as a last resort in fields where there are defined "hot spots," that is, where the young grasshoppers are continuing to hatch in large numbers and continued chemical applications are not desirable.
In this situation, the tactic is to bury the eggs and hatching grasshoppers deep enough so that the young hoppers cannot make it to the surface. Trap strips If grasshoppers are present when tillage operations begin, it is probably possible to achieve adequate control by simply eliminating all green plant materials in a field. Once grasshoppers have fed and developed to the second stage of growth second instar in a field, they are usually mobile enough to move to adjacent crops when their existing food supply is exhausted.
In these fields, trap strips should be used to collect grasshoppers into a relatively small area. It will then be possible to control the insects quickly and economically using a minimum amount of insecticide.
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To make trap strips, cultivate a black guard strip 10 m wide around the outside of a field. Leave an unworked green strip of at least 10 m before resuming cultivation Figure Repeat the process as often as necessary to produce additional trap sites. All green vegetation must be eliminated between the trap strips if they are to be effective. The black guard strip is enough to ensure that grasshoppers will move promptly into the trap strips to feed.
However, this trap strip does not have enough vegetation to feed a large grasshopper population for more than one or two days. Trap strip effectiveness can be improved considerably by seeding the strips to wheat or spring rye several weeks before tillage begins. The migration of young grasshoppers from the cultivated guard strips to the trap strips may take several days. Once the migration is complete, the trap strips and a 10 m strip of any adjacent crop should be treated with an insecticide.
The young grasshoppers are very susceptible to insecticides. The highest application rate recommended for the insecticide used should be applied to ensure adequate control is achieved.
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Figure Trap strip around the perimeter of a field. Credit: Dan Johnson. Before cultivating the trap strips, wait three days to assess the effectiveness of the insecticide. If adequate control is not achieved after three days, it may be necessary to treat the trap strip again. When grasshoppers have been eliminated from the trap strip, it should be possible to complete tillage without fear of displacing large numbers of grasshoppers into the adjacent crops. 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:. The most serious economic damage due to grasshoppers will be 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. Feeding preference studies have shown that oats is an exception and 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 more preferred crops. 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 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 two grasshoppers per square metre. 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. 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.
Johnson, D. Topinka, and C. Grasshopper Description The name "grasshopper" has been given to a very large and diverse group of insects. A mature two-striped female grasshopper Melanoplus bivittatus. Note the distinct two stripes running he 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. Figure 3. Spur-throated grasshoppers all possess a spur-like structure on their underside, just between where the front legs are attached. Figure 4. A migratory grasshopper Melanoplus sanguinipes. This pest grasshopper can be recognized by the dark bands just behind the eyes. Figure 5. An adult Packard grasshopper Melanoplus packardii settling in on an alfalfa plant. Most grasshoppers can eat from 30 to mg of dry weight material per day.
Figure 6. A fourth instar Packard grasshopper Melanoplus packardii. Note the green wingpads. Easily—and you can too. Get yours today before they run out! Get your new number before all the best ones are gone! Local Numbers A local number is one that starts with an area code specifically for a particular region, city, or state.
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