The Bunsen–Roscoe reciprocity law in ultraviolet-B-induced mortality of the two-spotted spider mite Tetranychus urticae

To determine whether the Bunsen–Roscoe reciprocity law (i.e., the extent of photochemical effects is determined by cumulative irradiance) is applicable to ultraviolet-B (UVB) damage in the twospotted spider mite Tetranychus urticae, egg hatchability and survival of individuals were assessed after irradiation with a UVB lamp using various combinations of intensity and time length. A positive linear correlation between probit mortality and cumulative UVB irradiance was detected in eggs, larvae, teleiochrysalis females, and adult females, regardless of UVB intensity (0.19–0.58 W m−2). LD50 values were clearly higher in adult females, followed by teleiochrysalis females, larvae, and eggs. In eggs, reciprocity was obeyed not only at the UVB intensities listed above, but also at very low UVB intensity (0.014–0.023 W m−2). Such reciprocity in the negative effects of UVB radiation was also observed for the developmental rate of juveniles and egg production of adult females. However, the LD50 value of eggs obtained using the UVB lamp (0.58 kJ m−2) was lower than that elicited by solar UVB radiation in a previous outdoor experiment (about 50 kJ m−2). These results suggest that a photoreactivation mechanism plays an important role in the survival of this mite under solar radiation.