What do locusts do to crops

The desert locust Schistocerca gregaria is a notorious species. Found in Africa, the Middle East, and Asia, this species inhabits an area of about six million square miles, or 30 countries, during a quiet period.

During a plague, when large swarms descend upon a region, however, these locusts can spread out across some 60 countries and cover a fifth of Earth's land surface.

Desert locust plagues threaten the economic livelihood of a tenth of humans. A desert locust swarm can be square miles in size and pack between 40 and 80 million locusts into less than half a square mile. Each locust can eat its weight in plants each day, so a swarm of such size would eat million pounds of plants every day.

To put it into context, a swarm the size of Paris can eat the same amount of food in one day as half the population of France. But experts can look at past weather patterns and historical records to identify the areas where swarms might occur and spray those areas with chemicals. Some experts worry that locust plagues will worsen in a warming world. Rising sea temperatures are causing prolonged bouts of wet weather, including a surge of rare cyclones in eastern Africa and the Arabian Peninsula where desert locusts thrive.

All rights reserved. Common Name: Locusts. Scientific Name: Acrididae. Type: Invertebrates. Diet: Herbivore. Group Name: Swarm. Average Life Span: Several months. They do not, as far as we know, carry any disease but some laboratory workers have developed an allergy to them.

The figure for hoppers is low because the breeding areas are mostly outside the main crop areas. The following illustrates the nature and degree of damage to both food and cash crops that can occur in the Desert Locust invasion area.

Bulrush millet Pennisetum americanum is a staple grain crop along the southern edge of the Sahara and in the Indo-Pakistan desert. It is much liked by the Desert Locust as a food plant and since it is grown extensively in areas which are highly frequented by this locust for breeding, considerable damage is caused; both leaves and ripe grain are destroyed Fig.

The staple food crop in areas receiving a slightly higher rainfall than the Pennisetum zones. Many varieties of this crop are not greatly liked by the Desert Locust during their main period of growth but the ripening grain of most varieties is readily attacked.

Heavy damage is caused, mainly by newly fledged swarms of the summer generation. Usually grown as a staple food crop in areas which are either too cool or too wet for the Desert Locust, but in parts of eastern Africa where it is grown under hotter and drier conditions than is customary for this crop, heavy damage does occur, the plants often being entirely defoliated and the cobs eaten away Fig.

Staple food crops in the spring breeding areas of the Desert Locust where they can be severely damaged, especially when they are approaching harvest. At this stage locusts bite through the last remaining moist part of the plant, the section of stem just below the ear, causing complete loss of grain, often without attacking the ear itself. Comparatively little damage is done to irrigated rice even in areas highly frequented by the Desert Locust, probably because the artificially wet conditions in which it is grown are not liked by this locust.

The effect of damage varies according to the stage of cane growth and the variety; for example, in Pakistan damage is greatest during the first four months of cane growth. This crop can be severely attacked.

The effect of damage on yield is great if it occurs just before flowering but less if it occurs afterwards. In the Desert Locust summer-breeding zone the start of cotton flowering generally coincides with the fledging of adult locusts and as the young adult is the stage at which most feeding takes place, this increases the danger to cotton in these areas. Coffee is rarely attacked. Occasionally defoliation of bushes occurs, but locusts do most damage at the flowering stage or when they settle on bushes in such large numbers that their weight breaks the branches.

These are particularly vulnerable to attack by immature swarms which have a preference for roosting in trees. Serious damage has occurred on oranges, lemons, pawpaw, dates and grapevines. Once damaged by locusts, the trees are liable to have their fruit yield affected for more than one year. Orange trees were very severely attacked in in Morocco Fig. It is not always fully realised how much damage can be done by locusts to natural grassland because it is generally less noticeable than damage to crops.

We know that in the. This is particularly important in areas where rangeland is not very good anyway and there can be widespread losses of cattle. During plagues, the last of which ended in , swarms of the African Migratory Locust invaded most of Africa south of the Sahara. And in response, "they become gregarious, attracted to each other. They eat more [and] develop faster," he said. Related: Grasshoppers vs. But the conditions must be just right for locusts to join forces. Sudden rainfall, for example, could help feed a growing population and cause flooding that corrals locusts together and attract more locusts to join.

What starts as a small group can turn into a thrumming swarm of thousands, millions or even billions of locusts. As part of this transformation, locusts may change color, Song said.

Some species of locusts become migratory, flying long distances across borders in search of food. The most devastating, best-known, and most frequently studied example is the desert locust Schistocerca gregaria.

The enormous swarms of desert locusts can be utterly devastating for famers whose livelihoods depend solely on those crops, she said. There are about 20 species of locusts, and they all undergo a dramatic transformation when there are many other locusts of the same species nearby. The locusts shift from what scientists call the solitarious, or solitary phase when the locust is alone, to the gregarious phase when they swarm together.

The specific signal that instigates the phase shift varies from species to species, Song said. For example, although both species react to the sight and smell of other locusts in a laboratory setting, the desert locust can shift into the gregarious phase with a touch on the hind legs, whereas the sensitive area on the Australian plague locust Chortoicetes terminifera is its antennae, he explained.

These triggers seem to boost levels of serotonin, the same chemical associated with mood in humans. Large swarms of locusts can completely strip the foliage and stems of plants such as forbs and grasses. Some species consume a variety of plants, while others have a more specific diet.

They often eat dry plant matter on the ground and will forage for weak or dead grasshoppers when plant food is scarce. As nymphs have a large appetite, they cause more damage than adults.

Locusts swarm when populations grow very large.