Photoeffects of Visible and Ultraviolet Radiation on the Two‐spotted Spider Mite, Tetranychus Urticae

The ability of the two‐spotted spider mite, Tetranychus urticae Koch, to detect and avoid various wavelengths was examined. The mites were given a choice between two regions: an area on a leaf exposed to light of defined spectral composition or an area protected from certain selected wavelength components. The mites showed little avoidance of visible, UV‐A or UV‐C wavelengths. In contrast, the animals strongly avoided the UV‐B spectral region, indicating that this arthropod can discriminate and respond to the presence of UV‐B wavelengths. The adult mites did not appear to be killed by the amount of UV‐B they could receive on a sunny summer day in Kentucky (i.e. 20 SU). However, the egg laying capacity of the females was reduced in a linear fashion as dose increased. Thus, avoidance of high UV‐B regions on a leaf may contribute to the survival of the species in nature.