Environment and host-plant genotype effects on the seasonal dynamics of a predatory mite on cassava in sub-humid tropical Africa

In tropical dry seasons, survival of small arthropods such as predatory mitesis often negatively affected by low relative humidity (RH). For species that donot diapause or migrate to refuges, the ability of the habitat to mitigate climaticconditions becomes crucial.2 The relative effect of macro-habitat (dry grassland hill, humid multiple croppingarea, humid riparian forest) and microhabitat (host-plant genotypes with hairy,semi-hairy and glabrous apices) on the seasonal dynamics of the phytoseiid miteTyphlodromalus aripo , a predator of Mononychellus tanajoa on cassava, wasexamined in a field experiment during a dry season. The effect of RH and plantgenotype on T. aripo egg survival was determined in an environment controlchamber.3 Predator abundance was higher in humid multiple cropping areas and on hairycassava compared with the other habitat types and cassava genotypes.4 Discriminant and regression analyses showed that the predator’s dry season persistencewas related to high RH, high plant vigour and hairy apices, but not toprey abundance.5 In the controlled climate experiment, the effect of host-plant morphology wasevident only at the intermediate RH level of 55%. An effect of apex hairiness wasnot found.6 It is concluded that the effect of genotype on T. aripo persistence diminishes underlow RH conditions, and that supportive effects of apex hairs become effectiveonly in the field, probably through protection from wind and/or intraguild predation.Humid multiple cropping areas planted with hairy and vigorous cassavagenotypes are suitable dry season reservoirs for T. aripo.