Analysis of biological control of cassava pests in Africa. III. Cassava green mite Mononychellus tanajoa.
Abstract
The interactions of the tetranychid Mononychellus tanajoa and cassava under West African weather and soil conditions were examined using a simulation model. Field studies had demonstrated the effects of plant and leaf age and rainfall-induced mortality on the population growth of M. tanajoa. The model showed that rainfall greatly reduced populations of the pest during the rainy season, while drought and nitrogen stresses acting indirectly via food availability were most important during the dry season. The combined effects of feeding by M. tanajoa and water and nitrogen stress on cassava tuber yield were assessed. The simulation data suggested that M. tanajoa would not be a severe problem on nitrogen-poor soils even with low rainfall-induced mortality, but the predicted yield reduction caused by poor soils was greater than the expected losses from feeding by the tetranychid on plants grown in good soils. The results also suggested that growing cassava under intensive irrigation and fertilization in an extended dry season could exacerbate the problems caused by M. tanajoa.