Strategies to Control the Desert Locust Schistocerca gregaria

The desert locust Schistocerca gregaria (Forskål) can infest an area from Mauritania to India and roughly from the Mediterranean to the Equator. Plagues with many swarms of adults and very many bands of hoppers are separated in time by recessions, when most of the locusts are scattered and confined to the 16 million square kilometre arid central belt. Widespread and heavy rain in the recession belt may lead to outbreak breeding. This may be followed by an upsurge during which successful breeding occurs in areas to which the adults of successive generations migrate. Further population increases lead to a plague. In spite of recent studies, the cost of the damage caused by the desert locust is not known and it is not clear whether the costs of control balance the costs of the damage that is prevented. Nevertheless, the impact on individual farmers may be devastating. Local crop protection is not feasible and financial compensation is difficult. However, the main importance of the desert locust is "political" since swarms are both dramatic and migrate between countries. The current strategy is to prevent plagues by controlling the outbreak or the early upsurge, despite the lack of field evidence that this is effective, and theoretical studies that suggest it is not. Adherence to such a preventive strategy, the irregular occurrence of plagues, and the fact that even during a plague many countries will escape, has led to plague crisis management. Donors have supplied aid, usually in the form of insecticides and aircraft, during upsurges and plagues with no adequate assessment of the need or of the capacity of the recipient country to use what is supplied. Much insecticide has remained in stock after plagues, creating a difficult disposal problem. Recent research and development has concentrated on: (1) processing of survey data with geographical information systems (GIS), (2) survey and application techniques using global positioning systems (GPS) and precision spraying, (3) physiological and ecological studies focussing on phase change, (4) barrier applications with new persistent insecticides, (5) use of biopesticides, especially mycopesticides and insect growth regulators, and (6) environmental monitoring. Hope for the discovery of some novel solution to the desert locust problem should not detract attention from improving campaign organization, as this will be required with any feasible new research finding. However, priority needs are to gather more information about recession populations, evaluate control campaigns, elaborate a new strategy for outbreak prevention, develop contingency plans for a plague campaign, and provide training in the execution of such plans when the need arises.

KEYWORDS desert locust, Schistocerca gregaria, strategy, outbreak, upsurge, plague, prevention, insurance, contingency plan