Phototaxis of Propsilocerus akamusi (Diptera: Chironomidae) From a Shallow Eutrophic Lake in Response to Led Lamps

Light pollution of freshwater ecosystems: principles, ecological impacts and remedies

Light pollution caused by artificial light at night (ALAN) is increasingly recognized as a major driver of global environmental change. Since emissions are rapidly growing in an urbanizing world and half of the human population lives close to a freshwater shoreline, rivers and lakes are ever more exposed to light pollution worldwide. However, although light conditions are critical to aquatic species, and freshwaters are biodiversity hotspots and vital to human well-being, only a small fraction of studies conducted on ALAN focus on these ecosystems. The effects of light pollution on freshwaters are broad and concern all levels of biodiversity. Experiments have demonstrated diverse behavioural and physiological responses of species, even at low light levels. Prominent examples are skyglow effects on diel vertical migration of zooplankton and the suppression of melatonin production in fish. However, responses vary widely among taxa, suggesting consequences for species distribution patterns, potential to create novel communities across ecosystem boundaries, and cascading effects on ecosystem functioning. Understanding, predicting and alleviating the ecological impacts of light pollution on freshwaters requires a solid consideration of the physical properties of light propagating in water and a multitude of biological responses. This knowledge is urgently needed to develop innovative lighting concepts, mitigation strategies and specifically targeted measures. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Phototactic Behavioral Response of the Ectoparasitoid Beetle Dastarcus helophoroides (Coleoptera: Bothrideridae): Evidence for Attraction by Near-Infrared Light

The ectoparasitoid beetle, Dastarcus helophoroides (Fairmaire) (Coleoptera: Bothrideridae), has been widely used as a biological control agent for many cerambycid beetles in China, Korea, and Japan. However, much less is known about its phototactic behavior to visual stimuli. In this paper, the phototactic behavioral response of D. helophoroides to 27 monochromatic lights and to nine illumination intensities of the most attractive light was evaluated using light-emitting diodes (LEDs) as light sources. The results showed that in dual choice between darkness and individual LED light, D. helophoroides adults exhibited a positively phototactic response to all wavelengths ranging from 300 to 860 nm. The near-infrared light (NIR, ranging from 700 to 760 nm) elicited stronger phototactic behavioral response, showing a preference for NIR wavelengths light. In paired choice among four preferred NIR lights, D. helophoroides adults displayed a significantly more favorable response to NIR light at 700 nm. Furthermore, the beetles expressed varying levels of sensitivity to illumination intensities from 1 to 600 lux under NIR light at 700 nm. The phototactic response was strongest at 7 lux and a statistically significant downward trend was found with increasing or decreasing the illumination intensities. These findings clearly demonstrate that D. helophoroides is a positively phototactic insect and its phototactic behavior is significantly influenced by light wavelength and illumination intensity, among which NIR light with peak wavelength at 700 nm and an intensity at 7 lux are most suitable in attracting D. helophoroides adults.

Impact of different wavelengths of artificial light at night on phototaxis in aquatic insects

The use of artificial light at night (ALAN) is increasing exponentially worldwide and there is growing evidence that ALAN contributes to the decline of insect populations. One of the most conspicuous ecological effects is the strong attraction of ALAN to flying insects. In several studies, light sources with strong short wavelength emissions have been shown to attract the highest numbers of flying insects. Furthermore, flying stages of aquatic insects are reported to be more vulnerable to ALAN than flying stages of terrestrial insects. This is concerning because freshwater habitats are likely affected by ALAN that originates from human activity centers, which are typically close to sources of freshwater. However, the effects of ALAN on aquatic insects, that spend their larval phase (amphibiotic insects) or their whole life cycle (fully aquatic insects) in freshwaters, are entirely understudied. Here, we investigated phototaxis of aquatic insects to ALAN at different wavelengths and intensities. We used floating light traps and compared four, near monochromatic, lights (blue, green, red and yellow) at two different photopic light intensities in a ditch system, which was not exposed to ALAN previously. Similar to flying stages of (aquatic and terrestrial) insects we found a strong positive phototaxis of aquatic life stages. However, in contrast to the flying stages there is no clear preference for short-wavelength light. Overall, responsivity to wavelengths in the center of the visible range (green, yellow; 500-600nm) was significant for all orders of aquatic insects studied and the nymphs of Ephemeroptera didn't respond to blue light at all. This is likely an adaption to how light is attenuated in freshwater systems, where not only the water itself but also a variety of optical constituents act as a color filter, often like in in our case filtering out short-wavelength light. Therefore, insects living in freshwater bodies often live in longer wavelength-dominated environments and might therefore be especially sensitive to green/yellow light. In conclusion, the different spectral sensitivities of both aquatic and flying insects should be taken into account when planning lighting near fresh water.