Temporal Variation in the Impact of Artificial Light at Night on Aquatic‐Terrestrial Insect Fluxes

Emergent aquatic insects play crucial ecological roles by providing resource subsidies that connect aquatic and terrestrial ecosystems. Artificial light at night (ALAN), however, is a growing anthropogenic factor that can impact insect behaviour; how ALAN might alter the timing, magnitude, community composition and other aspects of subsidy regimes remains poorly understood. Light‐emitting diodes (LED) are increasingly used across the globe and we experimentally added LED fixtures of four different wavelengths (red, green, violet and broad‐spectrum white) and a dark control to the littoral and riparian habitats of a pond. We sampled terrestrial and aquatic insect communities in littoral and riparian habitats on seven dates during the summer. Our goal was to determine how different wavelengths impacted insect community composition of a single pond as emergence composition shifted over the course of a summer. Insect abundance and biomass were greatest in violet treatments, but the magnitude of the effect strongly depended on sampling date. Differences in abundance and biomass were driven by taxon‐specific responses to wavelength, with emergent aquatic insects being more attracted to short‐wavelength light than terrestrial insects. Insect community composition was also dependent upon wavelength and sampling date. Our findings demonstrate that ALAN influences insect flux between habitats and that this depends on both wavelength and date. These findings suggest the impact of ALAN on littoral and riparian insect communities is more nuanced than previously assumed, and that temporal patterns in emergence should be considered in the management of ALAN at aquatic‐terrestrial boundaries.