VARIATIONS IN THE ABUNDANCE OF THE CASSAVA MEALYBUG, PHENACOCCUS-MANIHOTI, BEFORE AND AFTER THE INTRODUCTION INTO THE CONGO IN 1982 OF A MEALYBUG PARASITOID, EPIDINOCARSIS-LOPEZI (HYM, ENCYRTIDAE), OBTAINED FROM AMERICA

Variations in the abundance of the cassava mealybug, Phenacoccus manihoti, before and after the introduction into the Congo in 1982 of a mealybug parasitoid, Epidinocarsis lopezi (Hym. Encyrtidae), obtained from America. A detailed study in the Congo of the population dynamics and of the regulating factors of the cassava mealybug Phenacoccus manihoti five years after the introduction of the exotic parasitoid Epidinocarsis lopezi reveals the persistance of the outbreaks of this pest for the last nine years. Peak populations are observed particularly at the beginning of the rainy season. It has not been possible to show any correlation between parameters describing rains and the variation in the number of mealybugs. Our observations confirm that the Entomophthorale Neozygites fumosa is principally responsible for the reduction of the pest. The impact of the mealybug predators doesn't seem to be modified since 1979: the ladybird Exochomus flaviventris remains the more active predator. The parasitoid E. lopezi's acclimatation can be noticed by an increase of the parasitism level through a factor 2 to 3. However it has not permitted to modify the importance of the mealybug swarms. The abrupt increase in the number of mealybugs at the beginning of the rainy season is attributed to strong changes in the physiology of the host plant.