Light pollution has adverse effects on the overwintering of moths – new study could in part explain the decline in insect populations

An international team of researchers led by the University of Oulu observed that even faint light pollution at night prevents growing moth caterpillars from developing into overwintering pupae at the right time.

Many insects use daylength to synchronise their life cycle with the changing seasons, and the shortening days of late summer which indicate autumn getting closer, trigger the transition to the overwintering state as a pupa. If the days remain long, it suggests that a new generation can complete their life cycle before winter, which means that when light pollution leads moth caterpillars to erroneously interpret days as being long, the pupae immediately develop into adult moths. However, moths fooled by light pollution cannot successfully reproduce in autumn conditions or survive winter.

Published in the Journal of Applied Ecology on April 19th 2023 a new study tested how light pollution affects the development of the latticed heath (Chiasmia clathrata) caterpillars into overwintering pupae. In addition, the study compared populations in urban and rural environments to investigate possible genetic adaptations in urban populations, and it performed this comparison in both Mid European and Nordic countries.

According to the study, moths from the urban and rural populations have a similar, negative response to light pollution. This suggests that urban populations have not adapted to the urban environment filled with light pollution.

The populations in Mid Europe were more susceptible to light pollution than Nordic populations, which emphasises the need for decreasing the adverse effects of light pollution in southern latitudes, in particular. However, it is noteworthy that light pollution still had a negative effect also on the Nordic populations, which means that decreasing light pollution would also benefit Nordic moth populations.

“Light pollution has an increasing effect on nature and, according to our study, it seems that light pollution may also threaten insects’ successful overwintering,” says Academy Research Fellow Sami Kivelä from the University of Oulu. “Our research results are consistent with previous research, but the geographic variation in the susceptibility to the effects of light pollution and the fact that urban butterflies have not adapted to light pollution are new observations. Moving forward, studies should look at how widely insects are susceptible to the detrimental effects of light pollution, and to what extent it explains the decline of insect populations.”

“For mitigating the adverse effects of human activities on insects, our results are promising in the sense that this is a factor that can be fairly easily tackled,” states Professor Thomas Merckx from Vrije Universiteit Brussel. “We show that moths living in both urban and rural settings are sensitive to even dim levels of light pollution. Thus, decreasing light pollution should be a key priority in protecting insects, and in safeguarding the ecosystem services they provide us with.”
The Czech University of Life Sciences Prague was also involved in the study.

The research article: Thomas Merckx, Matthew E. Nielsen, Tuomas Kankaanpää, Tomáš Kadlec, Mahtab Yazdanian & Sami M. Kivelä (2023) Dim light pollution prevents diapause induction in urban and rural moths. Journal of Applied Ecology. doi.org/10.1111/1365-2664.14373

Read more: Urban butterflies and moths have evolved adaptations that extend their flight season