ECOLOGY AND PATHOGENICITY OF THE HOPLOLAIMIDAE (NEMATA) FROM THE SAHELIAN ZONE OF WEST-AFRICA .2. LABORATORY STUDIES ON SCUTELLONEMA-CAVENESSI SHER, 1964

The biology of S. cavenessi was affected by soil temperature, soil moi sture, host plant, present and previous host plants, length of the act ive contact between nematode and host plant, age of the nematode, and the previous physiological state of the nematode (hydrobiotic vs anhyd robiotic) before inoculation. This species appeared to be well adapted to the ecological conditions of the semi-arid tropics of West Africa : it is polyphagous, reproducing at relatively high soil temperature ( 32-34 degrees C) and low soil moisture (> 5%), with a life cycle of 10 0 days corresponding to the duration of the rainy season. Anhydrobiosi s affected the physiology of the nematode in its reproductive activity . These biological characteristics might explain the geographical dist ribution according to the soil temperature and the variations of popul ation densities according to the rainfall in the semi-arid tropics of West Africa. The study of the population dynamics showed that two peri ods occurred, the first corresponding to the reproductive activity of nematodes after anhydrobiosis at the end of the dry season, the second to that of nematodes produced from this first period. No pathogenic e ffects of the nematode to pluvial crops were recorded; this confirms p revious field observations, showing that pathogenicity of S. cavenessi appeared doubtful.