In the major breeding areas of tropical migratory locust, Locusta migratoria migratorioides (R. & F.) in Mali, Chad, Sudan and Madagascar, man has played a vital role in maintaining locust numbers above the levels found in undisturbed environments, through his agricultural and pastoral activities. Recent rapid agricultural development, particularly broad-acre cultivation of mono-cotyledonous summer crops in areas climatically suitable for migratory locust, has caused population upsurges in new areas, which have occasionally led to outbreaks and plagues. Some outbreaks appear to have been a reaction to the initial disturbance and have never recurred while others recur when meteorological conditions are favourable. Continued agricultural development in tropical and sub-tropical areas of the Old World will bring the risk of further upsurges of tropical migratory locust.
