EFFECTS OF FIELD POPULATIONS OF CASSAVA MEALYBUG, PHENACOCCUS-MANIHOTI, ON CASSAVA YIELD AND EPIDINOCARSIS-LOPEZI AT DIFFERENT PLANTING DATES IN NIGERIA

In experiments on the relation between Phenacoccus manihoti Matile-Ferrero, Epidinocarsis lopezi De Santis, and cassava yields, cassava planted early in the season significantly out-yielded late planting. The time of planting and P. manihoti populations had significant effects on root and stem yields. The combined effects of time of planting and P. manihoti populations accounted for higher percentage variability in the yields. E. lopezi increased in numbers with increasing numbers of its host, P. manihoti. The apparent inability of E. lopezi to regulate field populations of P. manihoti may be partly due to the incidence of indigenous hyperparasitoids such as Prochiloneurus insolitus Alam, P. sp. nr boliveri Mercet and Chartocerus sp. It is suggested that E. lopezi could be used effectively to reduce field populations of P. manihoti if released at low densities of P. manihoti in the late cassava crop. © 1990 Taylor and Francis Ltd.