Studies on mealybug (Planococcoides njalensis (Laing)) nutrition: a comparative analysis for the free carbohydrate and nitrogenous compounds in cocoa bark and mealybug honeydew

Abstract

To obtain dietary information for the laboratory rearing of Planococcoides njalensis (Laing) the bark tissue of cocoa shoots and mealybug honeydew were analysed for their free sugar and amino acid contents. Paper chromatographic analysis showed the bark tissue to contain mainly sucrose, with smaller amounts of glucose, fructose and raffinose. The proportions of sucrose and glucose+fructose in the honeydew were 24–27% and 24–35%, respectively, with the bulk of the 80% ethanol fraction composed of ketose oligosaccharides. The latter compounds may result from the glycosyltransferase action of mealybug invertase which has been partially characterised. Of the free nitrogenous substances, ethanolamine, asparagine, cysteine, lysine and γ-aminobutyric acid, alanine and glutamic acid are preferentially absorbed. It is concluded that these are important mealybug metabolites, which may be supplied with small amounts of sugar in future liquid-diet trials. Their approximate physiological concentrations were estimated by a semi-quantitative method.