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Science et changements planétaires / Sécheresse

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Quelques effets de la sécheresse sahélienne sur la dynamique des populations acridiennes Volume 7, issue 2, Juin 1996

Author
Département d’entomologie du Muséum d’histoire naturelle, Cromwell Road, Londres SW7 5BD, Grande-Bretagne
  • Page(s) : 91-7
  • Published in: 1996

In recent years, Sahelian Africa has undergone two periods of catastrophic drought : from 1968 to 1973 and 1980 to 1984. The impact of this widespread major meteorological event on the population dynamics of two acridid pest species, the African migratory locust Locusta migratoria migratorioides and the Senegalese grasshopper Oedaleus senegalensis, is examined. In the case of the migratory locust, the drought, coupled with anthropogenic activities, drought profound long-term environmental changes generally unfavourable to the locust. On the other hand, the large-scale development of meso-hygrotrophic habitats along the shores of lake Chad and its affluents following the retreat of water favoured proliferation of the species, at times leading to serious outbreaks. The outbreaks of Senegalese grasshopper during the 1974 to 1980 and 1985 to 1990 periods across the Sahelian zone are of a more complex nature. Various theories, based on the exceptional resistance of grasshopper eggs to drought, a decline in number of natural enemies, and erratic, insufficient rainfall, have been proposed. It is considered that during drought periods all these factors contribute year after year to a gradual build-up of Oedaleus senegalensis populations, culminating in outbreaks following rapido proliferation when rainfall returns to a more normal regime.