The western flower thrips, Frankliniella occidentalis Pergande and the onion thrips, Thrips tabaci Lindeman are major pests of Satsuma Mandarin (Citrus unshiu Marc.) fruits under greenhouse culture. To use thrips’ phototactic behavior for plant protection, we first determined the spectral sensitivity of the compound eyes of T. tabaci by recording electroretinogram. We then measured the action spectrum of phototaxis in flight activity in both species. Also measured the correlation between attractiveness of light and air temperature in both species. The compound eye spectral sensitivity exhibited two large sensitivity bands each peaking at 362 nm and at 532 nm. Both F. occidentalis and T. tabaci were strongly attracted to wavelengths around 350 nm. The attractiveness of 350 nm light was much stronger than that of 525 nm. The number of attracted individuals decreased as the air temperature dropped. We examined whether ultraviolet-emitting traps reduced the damage to fruits due to the thrips in greenhouses. As a result, ultraviolet-emitting traps were as effective as spraying of insecticides, Clothianidin and Acephate. Extensive browning on peels was found in the fruits irradiated with the light whose wavelength was shorter than 300 nm.