UV tolerance in the two-spotted spider mite, Tetranychus urticae

The two-spotted spider mite, Tetranychus urticae was exposed to UV-C (250 nm), UV-B (300 nm), and UV-A (350 nm). In non-diapausing females, the median effective doses for 50% mortality plus escape incidence (ED₅₀) were 21 (UV-C) and 104 kJ m⁻² (UV-B); those for 50% oviposition rate in continuous darkness-treated mites were 6.2 (UV-C) and 41 kJ m⁻² (UV-B). No significant effects of UV-A on mortality and oviposition rate were observed. The ED₅₀ values for UV-B were similar to the natural UV-B observed for 2-5 days in summer when T. urticae inhabits the undersides of leaves. Therefore, T. urticae possibly uses leaves as a filter to avoid the deleterious effects of UV-B. In diapausing females, low mortality was observed even at high doses of UV radiation, but more than half escaped even at low doses. The orange body color of diapausing females results from accumulation of carotenoids, a scavenger for UV-induced reactive oxygen species; this may explain the low mortality of diapausing females. Diapausing females may overcome the deleterious effects of UV-B during winter in the absence of leaves by emigrating to UV-free environments and by accumulating carotenoids.