Artificial light at night (ALAN) has been implicated as a contributor of insect decline worldwide. In New Zealand, little is known about the effect of artificial lights on freshwater insects. Light can attract freshwater insects from their flight path along rivers and result in a loss of recruitment back into the river. Changes in artificial light technology, particularly the development of light-emitting diode (LED) bulbs, which are more energy efficient than older high-intensity discharge or fluorescent lamps, has led to a widespread conversion of outdoor lighting to LEDs. LED lights vary in wavelength profile; shorter wavelengths of light (UV, blue, and green) are more visible to adult insects than longer wavelengths (yellow, orange, and red). Therefore, freshwater insects are expected to be affected more by cooler white LEDs (6500 Kelvin (K)) that have a greater peak in blue light intensity than warmer colour temperatures (3000 K). To gain a better understanding of the influence of LEDs on adult caddisflies, a first experiment compared four white LEDs (3000, 4000, 5650, and 6500 K) at one urban and one back-country river in Canterbury, New Zealand. A second experiment investigated how LED lights at distances between 0- 100 m from rivers affects the attraction of adult caddisflies.
Moths, flies, and a total of 26 caddisfly species were collected from two rivers. Results show the spectral composition of LED light influences the abundance of caddisflies attracted, as significantly more caddisflies were caught by 6500 K LEDs compared to 3000 K, likewise for 5650 K compared to 4000 K. The number of caddisflies attracted to LEDs significantly declined with increasing distance from the river, consistent across most caddisfly taxa trapped. These results indicate it would be pertinent to consider the ecological implications of different colour temperature LEDs and their spatial position as project design considerations.