Introduction

Many acridoid species are known to undertake long-distance migratory flights (Farrow, 1990). The migrations of gregarious-phase locusts are a well-known phenomenon (Rainey, 1951, 1963; Uvarov, 1977; Pedgley, 1981) but those of solitary locusts and grasshoppers have been observed only relatively recently, over the past 30 to 40 years (Golding, 1948; Davey, Descamps & Demange, 1959; Waloff, 1963; Têtefort, Dechappe & Rakotoharison, 1966; Botha & Jansen, 1969; Launois, 1974b; Lecoq, 1975, 1978a,b). For the last 20 years, French scientists now at CIRAD-PRIFAS in Montpellier have studied the factors influencing the migrations of solitary locusts and grasshoppers and their role in the events leading to outbreaks of pest species. The work has led to the development of survey and warning systems for three of these, the Migratory Locust, the Senegalese Grasshopper and, more recently, the Desert Locust (Lecoq, 1991a). This chapter describes the work on the Migratory Locust Locusta migratoria capito in Madagascar (with a brief reference to L. m. migratorioides in West Africa) and the Senegalese Grasshopper Oedaleus senegalensis in West Africa.

Flight movements and a warning system for the Malagasy Migratory Locust

Occurrence and importance of flight movements

In Madagascar, gregarisation of L. m. capito often begins in an extensive outbreak area in the southwest of the country and swarms originating here may subsequently invade the entire island (Fig. 19.1).