Reduced flight-to-light behaviour of moth populations exposed to long-term urban light pollution

Abstract

The globally increasing light pollution is a well-recognized threat to ecosystems, with negative effects on human, animal and plant wellbeing. The most well-known and widely documented consequence of light pollution is the generally fatal attraction of nocturnal insects to artificial light sources. However, the evolutionary consequences are unknown. Here we report that moth populations from urban areas with high, globally relevant levels of light pollution over several decades show a significantly reduced flight-to-light behaviour compared with populations of the same species from pristine dark-sky habitats. Using a common garden setting, we reared moths from 10 different populations from early-instar larvae and experimentally compared their flight-to-light behaviour under standardized conditions. Moths from urban populations had a significant reduction in the flight-to-light behaviour compared with pristine populations. The reduced attraction to light sources of 'city moths' may directly increase these individuals' survival and reproduction. We anticipate that it comes with a reduced mobility, which negatively affects foraging as well as colonization ability. As nocturnal insects are of eminent significance as pollinators and the primary food source of many vertebrates, an evolutionary change of the flight-to-light behaviour thereby potentially cascades across species interaction networks.

Keywords: Lepidoptera; Yponomeuta; adaptation; environmental change; natural selection.

Figure 1.

Flight-to-light behaviour of small ermine moths from dark-sky and light-polluted populations. (a) Proportion (mean ± s.e. across all populations) of small ermine moths attracted by artificial light under controlled experimental conditions. Overall, moths from populations which have been experiencing extensive light pollution are significantly less attracted to the light than moths from populations without light pollution (dark sky; p = 0.036). (b) Larvae of the small ermine moth (Yponomeuta cagnagella) on its host plant European spindle (Euonymus europaeus). (c) Adult small ermine moth. Scale bars, 5 mm. (Online version in colour.)