A Biochemical Investigation of the Taxonomy of the Cassava Green Mite Mononychellus Spp. (Acari: Tetranychidae) in Kenya

Abstract

Biochemical methods have been applied to elucidate the species systematics of cassava green mite (CGM). Traditionally CGM have been classified using the length of the dorso-central setae (D1-D3 ), which groups CGM into two species, the short setae form, Hononychellus tanajoa (Bandar) and the long setae form Mononychellus progresivus Doreste. However the validity of this method of classification is being questioned because the setae were found to vary from short to long in a continuous gradient. This characteristic, therefore becomes unreliable for species separation. Isoenzyme analysis and cuticular hydrocarbon studies were carried out using isoelectric focusing and gas chromatography respectively. Thirteen enzyme/substrate systems were used in distinguishing closely related species. These were; Aconitate hydratase, alcohol dehydrogenase, glucose-6-phosphate dehydrogenase, i.socitrate dehyrogenase, malate dehydrogenase, mannose phosphate isomerase malic enzyme, phosphoglucomutase, superoxide dimutase, nucleoside hydratase, hexokinase, glucose -viphosphate isomerase and pyruvate kinase. Out of the thirteen, three enzymes proved most powerful as taxonomic indicators, namely; malic enzyme, glucose phosphate isomerase and rnalate dehydrogenase. CGM populations showed identically migrating bands for these enzymes. Multivariate analysis was applied to demonstrate the statistical significance of the electrophoretic data. No major significant differences were observed within the band parameters. Hexane soluble cuticular hydrocarbons of the short and long setae forms, were separated by gas chromatography. The chromatographic profiles were identical for the two setal forms. It is clear from these results that there are no biochemical variants in CGM populations of Kenya. Consequently, there is no evidence to warrant species differentiation. Only a single species of CGM~ Mononychellus tanajoa can be considered to occur in Kenya.