Desert locust
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? Desert Locust |
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 Desert locust in solitary phase
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| Schistocerca gregaria Forsskål, 1775 |
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Plagues of the desert locust (Schistocerca gregaria) have threatened agricultural production in Africa, the Middle East and Asia for centuries. The livelihood of at least one-tenth of the world’s human population can be affected by this hungry insect. The 2004 desert locust outbreak has caused significant crop losses in West Africa and had a negative impact on food security in the region. It was one of the main factors contributing to the famine in Niger.
Desert locust ecology
The desert locust lives a solitary life, until it rains. Rain causes vegetation growth and spurs the development of eggs that have been laid in the sandy soil. The new vegetation provides food for the newly hatched locusts and provides them with shelter as they develop into winged adults.
When vegetation is distributed in such a way that the nymphs, usually called hoppers, have to congregate to feed, and there has been sufficient rain for a lot of eggs to hatch, forced physical contact causes the insects' hind legs to bump up against one another. This triggers a cascade of metabolic and behavioral changes that signal the insects' transformation from solitary behaviour to gregarious behaviour. When the locusts become gregarious they change from green coloured to yellow and black, their bodies become shorter, and they give off a pheromone that causes them to be attracted to each other, enhancing hopper band and subsequently swarm formation. Interestingly, the nymphal pheromone is different from the adult one. When exposed to the adult pheromone, hoppers become confused and disoriented, because they can apparently no longer "smell" each other, though the visual and tactile stimuli remain. After a few days, the hopper bands disintegrate and those that escape predation become solitary again. Maybe this effect could aid locust control in future.
During quiet periods, called recessions, locusts are confined to a 16-million-square-kilometer belt that extends through the Sahara Desert in northern Africa, across the Arabian Peninsula, and into northwest India. When conditions are right swarms invade countries on all sides of the recession area, as far north as Spain and Russia and as far east as India and southwest Asia. As many as 60 countries can be affected.
Swarms regularly cross the Red Sea between Africa and the Arabian Peninsula and are even reported to have crossed the Atlantic Ocean from Africa to the Caribbean. A single swarm can cover 1200 square kilometers and can contain between 40 and 80 million locusts per square kilometer. The locust can live between three to six months, and there is a tenfold increase in locust numbers from one generation to the next.
Crop loss
Desert locusts can consume the approximate equivalent of their body mass each day (2 g) in green vegetation: leaves, flowers, bark, stems, fruit, and seeds. Nearly all crops, and non crop plants, are at risk, including millet, rice, maize, sorghum, sugarcane, barley, cotton, fruit trees, date palm, vegetables, rangeland grasses, acacia, pines, and banana.
Crop loss from locusts was noted in the Bible and Qur'an. During the twentieth century, Desert Locust plagues occurred in 1926-1934, 1940-1948, 1949-1963, 1967-1969 and 1986-1989. The significant crop losses caused by swarming desert locusts, exacerbate problems of food shortage, and are a threat to food security.
Control
NASA has developed methods for detecting conditions and regions likely to give rise to swarms by satellite. Satellite data, combined with weather information and ground surveys, are used by the FAOs Desert Locust Information Service to produce forecasts published on the Web and in regular locust bulletins. They also provide information and training to affected countries and arrange for funding from donor agencies in case of major upsurges and plagues.
The desert locust is a difficult pest to control, and control measures are made more difficult by the large and often remote areas (16-30 million sq. km) where locusts can be found. Undeveloped basic infrastructure in some affected countries, limited resources for locust monitoring and control and political turmoil within and between affected countries further reduce the capacity of a country to prevent swarms.
An ecological methode to control desert locust is with natural enemies. These include predatory and parasitic wasps and flies, predatory beetle larvae, birds, and reptiles. The downside is that they are easily overwhelmed by the sheer magnitude of most swarms and bands if these were to be the ony defense used in a serious outbreak. However, they can help poor farmers since they might change the direction the swarm is heading. Another old African method is by putting poisonous or aromatic plants next to the crop they are trying to protect.
At present the primary method of controlling desert locust swarms is with organophosphate insecticides applied in small concentrated doses by vehicle-mounted and aerial sprayers. The insecticide must be applied directly to the insect. Control is undertaken by government agencies in locust affected countries or by specialised organisations like the Desert Locust Control Organisation for East Africa (DLCO-EA).
Biopesticides
Biopesticides include fungi, bacteria, neem extract and pheromones. The effectiveness of many biopesticides equals that of conventional chemical pesticides, but there are two distinct differences. Biopesticides take longer to kill the insect, plant diseases or weeds, between 2 and 10 days. More importantly, while there are approximately 25 million cases of severe work-related pesticide poisoning in developing countries each year, biopesticides are harmless to other creatures and the environment.
There are two types of biopesticides - biochemical and microbial. Biochemical pesticides are similar to naturally occurring chemicals and are non-toxic, such as insect pheromones use to locate mates, while microbial insecticides like Green Muscle® come from bacteria, fungi, algae or viruses that either occur naturally or are genetically altered. They generally suppress pests by producing a toxin specific to the pest or by causing a disease.
A biological control product has been available since the late nineties. It is based on a naturally occurring entomopathogenic fungus (i.e. insects-infecting fungus) , Metarhizium anisopliae var. acridum. The species M. anisopliae is widespread throughout the world infecting many groups of insects, but it is harmless to humans and other mammals and birds. The variety acridum has specialised on short-horned grasshoppers, to which group locusts belong, and has therefore been chosen as the active ingredient of the product.
The product is available under different names in Africa and Australia. It is applied in the same way as chemical insecticides but does not kill as quickly. At recommended doses, the fungus typically takes two to three weeks to kill up to 90% of the locusts. For that reason, it is recommended for use mainly against hoppers, the wingless early stages of locusts. These are mostly found in the desert, far from cropping areas, where the delay in death does not result in damage. The advantage of the product is that it affects only grasshoppers, which makes it much safer than chemical insecticides. Specifically, it allows the natural enemies of locusts and grasshoppers to continue their beneficial work. These include birds, parasitoid and predatory wasps, parasitoid flies and certain species of beetles. Though they cannot always prevent plagues, they can limit the frequency of outbreaks and contribute to their control.
New Control Methods
The LUBILOSA project was initiated in 1989 in response to environmental concerns over the heavy use of chemical insecticides to control locusts and grasshoppers during the 1986-89 plagues. The project focuses on the use of beneficial disease-causing micro-organisms (pathogens) as a biological control agent for grasshoppers and locusts. These insects were considered to be too mobile and to reproduce too fast to be readily controlled by a classical biological control.
Pathogens have the advantage that they can be produced in artificial culture in large quantities and be used with ordinary spraying equipment. The entomopathogenic fungus is traditionally seen as needing humid conditions to work well. The LUBILOSA project has found a way to avoid this by spraying fungal spores in oil. Even under desert conditions the biopesticide developed by LUBILOSA, called Green Muscle®, can be used to kill locusts.
2004 Desert locust outbreak
In 2004, West Africa faced the largest desert locust outbreak in 15 years. The costs of fighting this outbreak have been estimated by the FAO to have exceeded US$60 million and harvest losses were valued at up to US$2.5 billion which had disastrous effects on the food security situation in West Africa. Lack of rain and cold temperatures in the winter breeding area of Northwest Africa slowed down the development of the locusts and allowed the locust control agencies to stop the cycle. In 2005, only a couple of swarms invaded the Sahel countries. Though significant breeding occurred in the summer in the border area of Chad and Sudan, the situation appears to be under control for the time being.
The countries affected by the 2004 outbreak were Algeria; Burkina Faso; the Canary Islands, Cape Verde; Chad; Egypt; The Gambia; Guinea; Libyan Arab Jamahiriya; Mali; Mauritania; Morocco; Niger; Saudi Arabia; Senegal; Sudan; Tunisia; Yemen