Integrating cassava varieties and <i>Typhlodramulus aripo</i> to sustain biological control of cassava green mite

Abstract

The cassava green mite (CGM), Mononychellus tanajoa, is a pest that reduces root yield of cassava (Manihot esculenta Crantz) by 30-80% in the cassava belts of Africa. The objective of this study was to identify cassava varieties that enhance abundance and persistence of Typhlodramulus aripo on cassava and increase its efficiency in controlling CGM. Nine cassava (Manihot esculenta Crantz) varieties were evaluated in Kenya based on CGM abundance and HCN of leaves for their ability to sustain low CGM populations to enhance biocontrol of T. aripo. Cassava fields were surveyed in five agro-ecological zones in Uganda and samples of cassava apices were analysed for cassava varieties to sustain high population of T. aripo. In the screening study of CGM abundance and HCN content of leaves and the lowest cumulative CGM population densities (<1200 mites/leaf) were recorded on MM97/3567, Tajirika and MM96/9308, with the lowest cyanide content of leaves, 8.5 ± 4.9, 12.5 ± 3.2 and 12.3 ± 2.5 mg kg^-1, respectively. Cassava varieties with hairy and non-hairy tips sustained T. aripo with highest densities (0.96 actives per tip) on hairy TME14. High T. aripo population densities corresponded to high densities of hairs on cassava tips. There were significant inverse linear relationships between CGM densities and T. aripo on TME14 at moderate CGM population densities (CGM damage level 2).

Key Words: Cyanide, Manihot esculenta, Mononychellus tanajoa