Influence of Host plants and populations of the Mango mealybug, Rastrococcus invadens and its Natural enemies in the Guinea savanna, Nigeria

Abstract

The field populations of Rastrococcus invadens Williams and its parasitoid Gyranusoidea tebygi Noyes, predators and hyperparasitoids were monitored on Mangifera indica L., Plumeria alba L., Citrus sinensis L., Ficus umbellata (Vahl.) and Psidium guajava L. in the Guinea Savanna zone of Nigeria between November, 1996 and January, 1997. Population density of R. invadens was significantly higher on M indica and P. alba (P < 0.05) than on other hosts. Fluctuation in mealybug populations assumed a similar pattern on M indica, C. sinensis and P. alba. There was a relationship between the individual weather factor and R. invadens population, depending on the host plants. The three weather factors significantly (r2 = 373.2%, 80.8; P<0.05) influenced R. invadens population level on M indica and P. alba, respectively. While temperature contributed positively to fluctuation in the mealybug population, relative. humidity and winds contributed negatively to changes in its population level. G. tebygi attacked R. invadens on the five host plants throughout the period of study. Population trend of the parasitoid did not follow closely that of its host mealybug on the plant species. The rate of parasitism was lowest on P. alba (4.6%) and highest on P. guajava (32.1%). Generally, population trend of G. tebygi followed closely that of its hyperparasitoids. Reduction in parasitism of R. invadens by hyperparasitoids was significantly different on M indica and P. alba (P<0.05) compared with other plant species. Reduction in parasitism was lowest on P. guajava (20.7%) and highest on P. alba (82.1%) on which rate of parasitism of the mealybug was lowest. Among the hyperparasitoids, Chartocerus hyalipennis (Hayat), followed by Marietta leopardina :(Motsch) contributed mainly to reduction in parasitism. While M indica was the most favoured host of R. invadens, parasitism occurred most on P. guajava while hyperparasitism occurred most on P. alba.