Desert Locust are always present somewhere in the deserts between Mauritania and India. If good rains fall and green vegetation develop, Desert Locust can rapidly increase in number and within a month or two, start to concentrate, gregarize which, unless checked, can lead to the formation of small groups or bands of wingless hoppers and small groups or swarms winged adults. This is called an OUTBREAK and usually occurs with an area of about 5,000 sq. km (100 km by 50 km) in one part of a country.
If an outbreak or contemporaneous outbreaks are not controlled and if widespread or unusually heavy rains fall in adjacent areas, several successive seasons of breeding can occur that causes further hopper band and adult swarm formation. This is called an UPSURGE and generally affects an entire region.
If an upsurge is not controlled and ecological conditions remain favourable for breeding, locust populations continue to increase in number and size, and the majority of the infestations occur as bands and swarms, then a PLAGUE can develop. A major plague exists when two or more regions are affected simultaneously.
Outbreaks commonly occur and only a few lead to upsurges. Similarly, few upsurges lead to plagues. The last major plague was in 1987-89 and the last major upsurge was in 2003-05. Upsurges and plagues do not occur over night; instead they take many months to develop.
Some recent upsurges are described in more detail on these pages. Please see the FAO Desert Locust Guidelines (in the Publications section) for more detailed information.