INFLUENCE OF RELATIVE-HUMIDITY ON LIFE-HISTORY PARAMETERS OF MONONYCHELLUS-PROGRESIVUS AND OLIGONYCHUS-GOSSYPII (ACARI, TETRANYCHIDAE)

Life-history parameters of Mononychellus progresivus Doreste and Oligo nychus gossypii (Zacher), 2 major mite pests of cassava in Africa, wer e determined in the laboratory at 3 constant relative humidities (30, 60, and 90% RH) obtained with saturated salt solutions. Experiments we re carried out in airtight boxes placed in an air-conditioned room at 26 +/- 1 degrees C and a photoperiod of 12:12 (L:D) h (illuminance 3,5 00 lux). Low (30% RH) and high (90% RH) air humidity had a negative ef fect on the life-history traits of both species compared with medium a ir humidity (60% RH). For both species, the strongest effect was obtai ned at 90% RH; e.g., no M. progresivus eggs hatched, and 96% of the im mature stages of O. gossypii died. Relative humidity is, thus, an impo rtant abiotic factor influencing the population dynamics of both speci es and may explain part of the decrease in populations observed in the middle to the end of the dry season and the virtual absence of mites during the wet season.