We studied spontaneous photon emission from kidney bean leaves infested with kanzawa spider mites, Tetranychus kanzawai Kishida (Acari: Tetranychidae). Strong photon radiation was observed from veins strongly infested with spider mites. Temporal changes in the total photon intensity can be described by two different logistic curves: the one was thought to be due to injury caused by the mites and the other due to induced responses. Photon intensity of the wavelength ranging from 500 to 700 nm increased monotonously soon after spider mites attacked. Photon intensity from 300 to 400 nm began to increase about 20 h after infestation and showed two peaks at about 72 and 120 h. The former phenomena may be the result of direct injury (physical stresses) and the latter to physiological (biochemical) actions related to defensive responses. These results suggest that photon measurement is a powerful tool for evaluating plant responses to herbivory.

We studied spontaneous photon emission from kidney bean leaves infested with spider mites. Strong photon radiation was observed from the leaf veins where spider mites were crowding. Photon emission intensity increased with the decreases in chlorophyll content and photosynthesis yield; these decreases represented the degree of damage caused by the pest. When both infested and un-infested leaves were put on the same wet cotton, photon emission from the un-infested leaf increased, too. Photon emission from the un-infested leaf might be induced by an aqueous elicitor released from the infested leaf. Such an elicitor activates the plant defense response. Therefore, it is suggested that photon emission from an infested leaf conveys information on the direct injury (physical stresses) and physiological (biochemical) actions associated with the defensive response.

We performed the spectral analysis of ultraweak-photon emissions from kidney bean leaves infested by the kanzawa spider mite, Tetranychus kanzawai Kishida (Acari: Tetranychidae). We also measured the spectrum of photon emissions from artificially wounded leaves, and compared the result with spectral data obtained from the mite-infested leaves. Photon emissions from both the mite-infested and wounded leaves primarily consisted of wavelengths ranging from 500 to 700 nm, and photon intensity at these wavelengths increased steadily after perturbation. In contrast, photon intensity of the miteinfested leaves at 300-400 nm exhibited only differential changes; it began increasing at 20 h, and showed two peaks at 72 and 120 h. We previously reported that photon emissions from infested leaves might be the result of both insect damage and plant self-protection. Plant defensive responses, such as herbivore-induced plant volatiles (HIPV), are induced by insect elicitors via insect damage. Therefore, photon intensity at 500-700 nm might be related to direct injury (physiological stress), while photon intensity at 300-400 nm may signify a physiological (biochemical)-action-related defensive response.