Leonard Gianessi
Since prehistoric times, plagues of desert locust (a large grasshopper that swarms) have threatened agricultural production in Africa, the Middle East, and Asia. It lives in arid habitat, extending from the north equator in Africa, the Red Sea coasts and the Near East, to south west Asia. This vast area is called the recession area; it doubles in size during plagues from 16 million square kilometers to an invasion area of around 29 million square kilometers, affecting 20% of the earth’s surface comprising 65 countries. Solitary locusts live at low densities and do not cause threats to crops, but under favorable conditions they rapidly breed to produce vast numbers of gregarious locusts that congregate to form swarms. Successful breeding is due to favorable conditions which occur as a result of widespread rainfall with the subsequent growth of vegetation cover; the locusts form hopper bands (groups of large numbers of immature stages that are flightless) and swarms(vast numbers of adults).Swarms may fly hundreds or thousands of kilometers downwind. The swarms may cover several hundred square kilometers during plagues and contain 50 million locusts per square kilometer. The locust consumes the approximate equivalent of its body mass every day in green vegetation; a square kilometer of locusts can
consume about 100 tons of crops per day. The plagues end as a result of control operations and the unavailability of favorable environmental conditions.
The aim of the preventive control strategy against the locust is to control formation of hopper bands in the breeding areas during upsurges, which is generally desert or semi-desert, to prevent formation of swarms and movement into agricultural areas. This requires regular monitoring of locust breeding areas, both remotely to monitor rainfall and vegetation growth and on-the-ground observations, and the ability to mount quick small scale control operations to halt growth into large swarms. Control operations are implemented if locusts are found in high gregarious densities. If swarms do form, aerial application of a fast-acting chemical pesticide, particularly when swarms rest, is required, as rapid knockdown of the insects is needed. Locusts have been controlled in Ethiopia and Somalia to protect crops in Kenya and Tanzania. Campaigns have been waged in Iran and Arabia to protect crops in India and Pakistan. Chemical insecticides are the principal means of controlling desert locusts [3]. Ground and aerial application of chemical pesticides is the only viable method of locust control on a large scale[4]. Recent development of biopesticides for locust control is only practical for hoppers prior to reaching agricultural areas as they take a number of days to work. The availability of these products is also limited. The preventive control strategy was founded in the 1960s and has had a major impact in reducing the frequency of desert locust plagues which were present in three-quarters of the previous years but in only 1 in 7 of the subsequent years [1]. Regular reports are made summarizing monitoring and preventive treatments in which 5-30,000 hectares are typically sprayed [2].
Monitoring locust breeding areas can be difficult as many are located in remote areas or are in areas inaccessible due to border disputes and lack of security. Major outbreaks can occur. When locust upsurges and plagues develop, large scale campaigns must be mounted. These campaigns use large quantities of insecticides [4]. In the plague of 1986-89, some 40 countries were affected and more than 14 million hectares were treated [4]. In the desert locust plague of 2003-2005, more than 13 million hectares were sprayed with about 13 million liters of chemical insecticides [4]. The collapse of the Soviet Union in 1991 led to a significant decrease in locust monitoring and preventive treatments resulting in a need to spray 8 million hectares in Kazakhstan in 2000 to prevent major crop losses [5].
In 2013, locust invasions occurred in Israel and Madagascar resulting in the need for widespread insecticide spraying to prevent major crop losses. The U.N. estimated that about 25% of Madagascar’s rice crop would be destroyed without treatment. Continued vigilance is required to manage locust outbreaks and mechanisms need to be in place to ensure that pesticides are available when needed in the right amounts, at the right time, and in the right place; this requires effective co-ordination between governments, donors and the private sector.
1. Dobson, H. M., and J. I. Magor. 1999. Ancient plagues and modern solutions: locust management in the new
millennium. BCPC Symposium Proceedings. 73:3-30.
2. FAO. 2013. Desert Locust Bulletin. No. 422.
3. Mamadou, A. and M. Sarr. 2009. Impact of two insecticides used in the control of the desert locust on
Psammotermes hybostoma Desneux (Isoptera: Rhinotermitidae) in Niger. African Entomology. 17[2]:147-153.
4. FAO. 2009. Workshop on Spray Equipment Used in Desert Locust Control.
5. Latchininsky, A. V., and Gapparov, F. 2007. Locust control in central Asia: migs versus micronairs. Outlooks on
Pest Management. June.
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