Artificial light at night may decrease predation risk for terrestrial insects

Artificial light at night (ALAN) is thought to be detrimental for terrestrial insect populations. Whilst there exists evidence for lower abundance under ALAN, underlying mechanisms remain unclear. One mechanism by which ALAN may contribute to insect declines may be through facilitating increased predation. We investigated this by experimentally manipulating insect-substitute abundance under differential levels of light. We used insect-containing birdfeed placed at varying distances from streetlights as a proxy for terrestrial insects, inspecting the rate of predation before and after dusk (when streetlights are respectively off and on). We found that there was a significantly greater effect of increasing distance on predation after dusk, suggesting that predation was actually reduced by greater levels of artificial light. This may occur because ALAN also increases the vulnerability of insectivores to their own predators. Implications for foraging behaviour and alternative explanations are discussed.

Methods
Predation of insect-proxies was estimated for a 6 hour period before and after dusk at 5 different distances at 7 different lampposts in St Andrews over several days.