Effects of artificial light on growth, development, and dispersal of two North American fireflies (Coleoptera:...

Holometabolous insects exhibit complex life cycles in which both morphology and ecological niche change dramatically during development. In the larval stage, many insects have soft, slow-moving bodies and poor vision, limiting their ability to respond to environmental threats. Artificial light at night (ALAN) is an environmental perturbation known to severely impact the fitness of adult insects by disrupting both temporal and spatial orientation. The impact of ALAN on earlier life stages, however, is largely unknown. We conducted a series of laboratory experiments to investigate how two distinct forms of ALAN affect the development and movement of immature Photuris sp. and Photinus obscurellus fireflies. Although long-term exposure to dim light at night (dLAN), akin to urban skyglow, did not impact overall survivorship or duration of egg, larval, and pupal stages in either species, it did accelerate weight gain in early-instar Photuris larvae. Late-instar Photuris exposed to point sources of ALAN at the start of their nightly foraging period were also significantly more likely to burrow beneath the soil surface, rather than disperse across it. ALAN may therefore impede dispersal of firefly larvae away from illuminated areas, which could have downstream consequences for the reproductive fitness of adults.