Quantitative knowledge of temporal and spatial distribution patterns of arthropod pests and their natural enemies is essential for understanding their interactions and is a prerequisite for the development of reliable sampling plans for estimating and monitoring pest and natural enemy abundance. Temporal and spatial distributions of the cassava green mite Mononychellus tanajoa (Bondar) (Acari: Tetranychidae) and its predator Typhlodromalus aripo DeLeon (Acari: Phytoseiidae) were determined in two cassava fields in Southern Benin, West Africa. Samples were taken to follow predator and prey dynamics at monthly intervals, from August 1998 (shortly after planting), to harvest time in June 1999. In addition, within-plant distribution of both predator and prey was determined in the upper 20 nodes of selected cassava plants on four occasions during the study period. In both field sites, temporal trends in abundance of M. tanajoa and T. aripo were similar but with a slight delay in T. aripo response to changes in M. tanajoa densities. Overall temporal trends of T. aripo and M. tanajoa in both study sites were related to seasonal rainfall pattern, as expected. Aggregation indices calculated using Taylor’s power law indicated that both predator and prey had a clumped distribution, but M. tanajoa distribution was less aggregated after the introduction of T. aripo compared with its previously determined aggregation when efficient predators of M. tanajoa were still lacking in Africa. Within plants, M. tanajoa occurred largely on young leaves; however, the highest densities shifted from the first fully developed leaf (c. leaf 4) to leaves 6–12 in the presence of T. aripo. This downward shift in M. tanajoa distribution on cassava plants is most likely caused by the foraging patterns of T. aripo, which forages within the upper part of the cassava foliage during the night hours and spends much of the daylight hours sheltered in the apex (apical domatium) of the plant. New enumerative sampling plans were developed for M. tanajoa and T. aripo on the basis of the new Taylor’s power law aggregation indices. Limitations of the proposed sampling plans in monitoring population densities of T. aripo and M. tanajoa are discussed.
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