Action spectrum for the suppression of arylalkylamine N-acetyltransferase activity in the two-spotted spider mite Tetranychus urticae

An action spectrum was obtained for the suppression of arylalkylamine N -acetyltransferase (NAT) activity in the two-spotted spider mite Tetranychus urticae by irradiating the mite with monochromatic lights of various wavelengths using the Okazaki Large Spectrograph at the National Institute for Basic Biology, Okazaki, Japan. Fluence–response curves were obtained for wavelengths between 300 and 650 nm by irradiating the mite for 4 h day⁻¹. The samples were frozen after the third exposure. A negative correlation between the logarithmic fluence rate and NAT activity was detected in the range of 0.01–1 μmol m⁻² s⁻¹ for wavelengths between 300 and 500 nm and in the range of 0.1–10 μmol m⁻² s⁻¹ for wavelengths between 550 and 650 nm. The constructed action spectrum indicated that the photoreceptors mediating the circadian and/or photoperiodic systems might be UV-A- and blue-type photoreceptors with absorption peaks at 350 and 450 nm.