POPULATION-DYNAMICS AND LIFE-TABLES OF THE MANGO MEALYBUG, RASTROCOCCUS-INVADENS WILLIAMS, AND ITS INTRODUCED NATURAL ENEMY GYRANUSOIDEA-TEBYGI NOYES IN BENIN

Life table data for Rastrococcus invadens and its introduced natural e nemy Gyranusoidea tebygi were obtained in the field and in the laborat ory. The mealybug population's potential rare of increase ranged from 0.066/day to 0.078/day. The potential for increase of the parasitoid w as double that of its host. Seasonal fluctuations in abundance of R. i nvadens were followed from 1988 to 1992 on mango trees in southern Ben in. The population density of R. invadens decreased during the rainy s easons and peaked during the dry seasons. Mealybug field sex ratios we re extremely variable, and the impact of such variability on the mealy bug's potential rate of increase was analyzed. The populations of the exotic encyrtid G. Tebygi, introduced into Benin in 1988 for control o f the pest, were synchronized with the host populations. The spatial p atterns of parasitism distribution in relation to the host population density were either independent or directly density-dependent, both at the tree level and for larger zones. However, reducing the scale of a nalysis resulted in different types of relationships. the impact of pr edators was a minor factor in the population dynamics of the mealybug. Four of the six species of hyper-parasitoids attacking mealybugs para sitized by G. tebygi developed high populations. In the two orchards s tudied, mealybug populations eventually collapsed and disappeared. Thi s fact is discussed as being an indication that the biological control of the mango mealybug by G tebygi was achieved by non-equilibrium loc al dynamics, and should be evaluated in a meta-population perspective.