Intraleaf Distribution of Panonychus ulmi (KOCH) : (Acarina : Tetranychidae) on Dwarf Bamboo

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Abstract
Seasonal and diel changes on leaf surface preferences by Sapporo populations of the European red mite, Panonychus ulmi (Koch), were studied throughout its life cycle on dwarf bamboo, Sasa senanensis (Franchet et Savatier). Mites overwintered as eggs, which hatched in May. Four or 5 generations were then produced, but by November, again only eggs were found. Non-diapause eggs, active immature stages and adult females were found predominantly on the uppersurface of the leaf, except during periods of low temperature or cloudy conditions. About half of the active stages that did populate the undersurface of the leaf were found predominantly near the leaf edge, but they were not able to feed on this surface. This fact suggests that the undersurface is a refuge from severe diurnal and nocturnal factors. Diapause eggs, quiescent stages and adult males were mainly found on the leaf undersurface. The position of the active stages changed daily on the leaf surfaces: in the daytime they appeared on the uppersurface of the leaves, whereas at night they were found on the undersurface. These movements appear to be controlled by a complex interaction among light intensity, air temperature and relative humidity.