Aerial Transport of Pests and Pest Outbreaks1

Pests of arable crops tend to show a high degree of migratory activity. This is particularly so in northern Sudan where the variable rainfall produces habitats which are short-lived and unpredictable in their frequency and location. Insects whose flight activity is adapted to enable them to move on the same wind-system which produces the rains are frequently pests of the crops of these climates. Outbreaks of such pests are usually a function of the numbers which colonise the crops, and this in turn depends not only on the success of breeding in the source areas but also on increases in density which occur whilst they are airborne. The importance of the increases in airborne densities which occur within the inter-tropical discontinuity and the cold-air outflows ahead of convectional storms to pest outbreaks in the Sudan Gezira is described.