Shedding light on moth declines

Moths

Back in 2004, when Rothamsted Research and Butterfly Conservation first uncovered the significant, long-term decline in moth abundance, artificial light at night (ALAN) was highlighted as a potential contributor to the observed trends1.

However, at that time, there was little scientific evidence with which to assess the likely impact; we knew that many moths (and other creatures) are attracted to light, which could result in higher mortality due to direct contact with hot lights and increased predation. 

Since then, research into the effects of ALAN on moths and other biodiversity has burgeoned. ALAN has been found to influence the makeup of invertebrate and plant communities, alter species phenology and have physiological and behavioural effects. In moths, for example, ALAN disrupts pheromone production in female Cabbage Moth (Mamestra brassicae)2, inhibits feeding in adult moths3 and reduces mating in Winter Moth (Operophtera brumata)4. In an intriguing, and potentially far-reaching, recent finding, individuals of the micro-moth Yponomeuta cagnagella from urban populations were found to be less strongly attracted to light than individuals from populations in areas of low ALAN, suggesting an evolutionary response driven by exposure to artificial light5

There are also likely effects of ALAN on the pollination services carried out by moths at night. Working on a Butterfly Conservation PhD project, in conjunction with the University of Newcastle and Centre for Ecology & Hydrology, Callum Macgregor recently discovered that streetlights disrupt the movement of moths in field margins on Oxfordshire farms. Among the ground vegetation, where pollination of wild flowers would take place, moths abundance was 50% lower and species richness 25% lower on lit versus unlit sections. This was shown to be a behavioural effect caused by the streetlights, not a community-level change between lit and unlit sites; the abundance of moths flying overhead was 70% greater at lit sites than dark ones6. A Swiss study has since shown a significant decrease in the number and species richness of nocturnal insect visitors to flowers in Alpine meadows when exposed to ALAN7

Butterfly Conservation’s key focus, however, remains on detecting population-level effects of ALAN on moths. There is, as yet, no firm link between artificial light and population change in any moth species, although a study published earlier this year found that moths that are nocturnal or that are known to be attracted to light had decreased more in the Netherlands over the past 30 years than day-flying species or those not attracted to light8. Butterfly Conservation aims to develop new research projects this year to shed further light on this potential driver of moth declines.

Richard Fox

Head of Recording, Butterfly Conservation

 

  1. Conrad, K.F., Woiwod, I.P., Parsons, M., Fox, R. & Warren, M. (2004) Long-term population trends in widespread British moths. Journal of Insect Conservation 8: 119–136. doi:10.1023/B:JICO.0000045810.36433.c6

  2. Van Geffen, K.G., Groot, A.T., Van Grunsven, R.H.A, Donners, M., Berendse, F. & Veenendaal, E.M. (2015) Artificial night lighting disrupts sex pheromone production in a Noctuid moth. Ecological Entomology 40: 401–408. doi:10.1111/een.12202

  3. Van Langevelde, F., Van Grunsven, R.H.A., Veenendaal, E.M. & Fijen, T.P.M. (2017) Artificial night lighting inhibits feeding in moths. Biology Letters 13: 20160874. doi:10.1098/rsbl.2016.0874

  4. Van Geffen, K.G., Van Eck, E., De Boer, R.A., Van Grunsven, R.H.A., Salis, L., Berendse, F. & Veenendaal, E.M. (2015) Artificial light at night inhibits mating in a Geometrid moth. Insect Conservation and Diversity 8: 282–287. doi:10.1111/icad.12116

  5. Altermatt, F. & Ebert, D. (2016) Reduced flight-to-light behaviour of moth populations exposed to long-term urban light pollution. Biology Letters 12: 20160111. doi:10.1098/rsbl.2016.0111

  6. Macgregor, C.J., Evans, D.M., Fox, R. & Pocock, M.J.O. (2017) The dark side of street lighting: impacts on moths and evidence for the disruption of nocturnal pollen transport. Global Change Biology 23: 697–707. doi:10.1111/gcb.13371

  7. Knop, E., Zoller, L., Ryser, R., Gerpe, C., Hörler, M. & Fontaine, C. (2017) Artificial light at night as a new threat to pollination. Nature 548, 206–209. doi:10.1038/nature23288

  8. Van Langevelde, F., Braamburg-Annegarn, M., Huigens, M.E., Groendijk, R., Poitevin, O., van Deijk, J.R., Ellis, W.N., van Grunsven, R.H.A., de Vos, R., Vos, R.A., Franzén, M. & WallisDeVries, M.F. (2018) Declines in moth populations stress the need for conserving dark nights. Global Change Biology doi:10.1111/gcb.14008