The susceptibility of cocoa to mealybugs (Pseudococcidae) and other honeydew-producing Homoptera in Ghana

Abstract

Population densities of mealybugs and other honeydew-producing Homoptera were assessed in six cocoa (Theobroma cacao Linnaeus) trials by inspecting trees from ground to eye level, and also by dissecting samples of terminal buds. A total of 68 cocoa progenies was examined, mainly inter-crosses of six clones. Progenies differed in their levels of infestation with total mealybugs, Planococcoides njalensis (Laing), Planococcus citri (Risso), Phenacoccus hargreavesi (Laing), (Pseudococcidae), Toxoptera aurantii (Boyer de Fonscolombe) (Aphididae), and Mesohomotoma tessmanni (Aulmann) (Psyllidae). Crosses with Amelonado or T63/971 were generally more densely infested with mealybugs than those for example of NA34 and T63/967. Trees of T17/524 parentage were sparsely infested with mealybugs. Rankings of progenies by infestation with mealybugs from the two different sampling procedures were positively correlated, but the relative abundances of individual mealybug species on the trunk and in the canopy differed. Several species of mealybug found in buds were either rare or never found by inspecting trees up to eye level. Correlations between rankings of progenies by order of abundance of Planococcoides njalensis and Planococcus citri were positive and statistically significant, as were those between mealybugs and infestation of buds by T. aurantii or M. tessmanni. The above rankings were negatively correlated with those by aphid and psyllid abundance assessed from inspecting trees up to eye level. The two sampling procedures were complementary but, for economy, samples of buds gave the clearest indication of a progeny's suitability for mealybugs.