Lethal effects of short-wavelength visible light on insects

Abstract

We investigated the lethal effects of visible light on insects by using light-emitting diodes (LEDs). The toxic effects of ultraviolet (UV) light, particularly shortwave (i.e., UVB and UVC) light, on organisms are well known. However, the effects of irradiation with visible light remain unclear, although shorter wavelengths are known to be more lethal. Irradiation with visible light is not thought to cause mortality in complex animals including insects. Here, however, we found that irradiation with short-wavelength visible (blue) light killed eggs, larvae, pupae, and adults of Drosophila melanogaster. Blue light was also lethal to mosquitoes and flour beetles, but the effective wavelength at which mortality occurred differed among the insect species. Our findings suggest that highly toxic wavelengths of visible light are species-specific in insects, and that shorter wavelengths are not always more toxic. For some animals, such as insects, blue light is more harmful than UV light. U nderstanding the influence of visible light (400-780 nm) on organisms is important for identifying novel uses and examining hazards of exposure to visible light. However, little is known about the biological toxicity of visible light. Although recent studies have described damage by short-wavelength visible light (blue light, 400-500 nm) to the mammalian retina, called the 'blue light hazard' [1][2][3][4][5] , there have been no reports on the lethal effects of irradiation with visible light on complex animals, including insects. On the other hand, the toxicity of shortwave UV light to organisms is well known. UVC (100-280 nm) and UVB (280-315 nm) induce mutagenic and cytotoxic DNA lesions 6,7 , and UVC irradiation has lethal effects on insects 8 and microorganisms 9 . The use of UVC irradiation for control of pests such as Tribolium castaneum, T. confusum, Cadra cautella, and Trogoderma granarium, which infest stored grains, has been studied 10,11 . Lethal effects of UVC against larvae of the silkworm Bombyx mori are also well known 12,13 . Lethal effects of UVB have been reported for spider mites 14 , in which UVB irradiation strongly decreases survivorship and egg production. However, there are no reports that describe lethal effects of UVB or UVA (315-400 nm) on insects, although UVA irradiation slightly decreases adult longevity in the lepidopteran Helicoverpa armigera 15. It is well known that shorter wavelengths of light are more lethal 9,16,17 . In addition, positive effects of wavelengths ranging from UVA to green (500-560 nm) have been reported for spider mites; irradiation with UVA, blue, and green light caused photoreactivation of mites damaged by UVB irradiation 18 . Therefore, irradiation with visible light is not considered lethal to complex animals, including insects. Here, in contrast, we show a strong lethal effect of blue light on insects. In this study, we found that blue-light irradiation by a common LED can kill insect pests of various orders and that highly lethal blue-light wavelengths are species-specific in i...