Remote sensing of rainfall by satellite as an aid to Oedaleus senegalensis (Orthoptera: Acrididae) control in the Sahel.
The acridid Oedaleus senegalensis is a major pest of subsistence crops in the West African Sahel. In northern Mali, O. senegalensis spends the dry season in the egg stage in the soil and eclosion is triggered by the 1st rains which usually occur in May and June. Satellite imagery potentially enables rainfall, and hence O. senegalensis eclosion, to be monitored over much wider areas than those possible for ground-based observers. In 1990 and 1991, rain-gauge networks were set up at Mourdiah, northern Mali, and for each storm event, rainfall and Meteosat infra-red data were collected. The coldest convection clouds (< -70°C) produced rain 93.1% (n = 15) of the time, whereas warmer cloud (> -10°C) produced rain only once (n = 61). The relationship between minimum cloud temperature and log transformed rainfall data was negative and highly significant (P < 0.0005). The maximum rain-gauge separation for reliable point measurements of rainfall was 8 km. Simulated rainfall experiments showed that the eclosion of O. senegalensis was influenced both by soil type and by the quantity of water added to the soil. A survey of O. senegalensis after the 1st rain in 1994 showed that 8 mm was sufficient to cause eclosion 9 days later. The implications of these results for the improved control of O. senegalensis control are discussed.