What Is The Impact of ALAN On Nocturnal Pollination By Moths?

Pollination is a fundamental ecological process that supports biodiversity and sustains economies through crop pollination. About 80% of wild plant species rely on insect pollination for seed set and fruit. Additionally, about 75% of crops used for human food rely on insect pollination. This means that insect pollination is highly important for biodiversity and agriculture world wide (Potts et al. 2010) While most might think of daytime pollinators such as bees and butterflies, nocturnal pollinators like moths, bats and beetles are vital for many plant species. Nocturnal insects are quite understudied compared to diurnal insects when it comes to pollination.

Importance of Nocturnal Pollination by Moths

In recent years it has become increasingly clear that moths (Lepidoptera) play an important role in pollination of plant species such as crops and medicinal plants. Over 227 moth-flower interactions are currently observed, many of which occur during the night when diurnal pollinators like bees are not foraging (Hahn & Brühl, 2016). Additionally, nocturnal pollination plays an ecological role in many non-crop plant communities (Buxton et al., 2022). The full scale and impact of nocturnal pollination by moths, however, should be more thoroughly studied as the currently available data is limited in both its methods and the number of families studied.

There are indications that moths might be more effective at pollinating than diurnal pollinators like bees for a number of reasons. Moths deposit pollen more efficiently (more pollen dropped compared to removed from a flower) while carrying pollen over greater distances. Additionally, moths mainly consume nectar from plants while bees also collect pollen to feed their larvae, thus reducing their efficiency for the plant (MacGregor et al. 2014).

A recent study shows that moths are declining for many of the same reasons as diurnal pollinators. In Great Britain, 260 moth species have seen population declines in the last 50 years. This decrease in population size is likely due to climatic and land-use changes (such as habitat loss and nitrogen deposition) (Fox et al. 2014). It has also become clear that moths face another challenge in urban environments: Artificial light at night (ALAN).

The Impact of ALAN on Moths

Light pollution has rapidly increased with the rise of technology and the invention of electric lighting. A study mapping light pollution across the world has found that 80% of the world’s skies are light-polluted with more than 99% of U.S. and European populations living under these light polluted skies (Falchi et al. 2016). In addition to helping us see at night, ALAN can trap nocturnal insects like moths at artificial light sources due to flight-to-light behaviour. This behaviour occurs due to the flying behaviour where nocturnal insects turn their dorsum to the lightsource. In natural conditions this behaviour allows for flight control and orientation. However, in the presence of ALAN it can lead to a circular flight path around the light source, which can trap an insect at the light source. The constant presence of street lights and lit up billboards can create high densities of individuals around the light source due to this flight-to-light behaviour (Fabian et al. 2024). This has been found to lead to increased predation due to bats and spiders that can exploit the high density of moths at these light sources. Furthermore, ALAN can negatively impact foraging and mating behaviour, thus severely affecting the natural nocturnal behaviour across entire urban and rural environments. These factors can combine to decrease fitness of moth populations in urban and rural areas (MacGregor et al. 2014).

Image of a streetlight showing a high density of insects surrounding it.

Conclusion

As there is evidence that ALAN might impact moth populations across the world, studies should be done into how we can preserve these important “butterflies of the night” and their ecosystem services. Knowing how ALAN affects pollinating behaviours, predation, and mating will give insight into the best solutions to these changes and how these can best be employed. Through this knowledge we will hopefully benefit from the ecosystem services of nocturnal pollinators for many years to come. 

 

References

1. Potts, S. G., Biesmeijer, J. C., Kremen, C., Neumann, P., Schweiger, O., & Kunin, W. E. (2010). Global pollinator declines: trends, impacts and drivers. Trends in Ecology & Evolution, 25(6), 345–353. https://doi.org/10.1016/j.tree.2010.01.007 
2. Hahn, M., & Brühl, C. A. (2016). The secret pollinators: an overview of moth pollination with a focus on Europe and North America. Arthropod-Plant Interactions, 10(1), 21–28. https://doi.org/10.1007/s11829-016-9414-3 
3. Buxton, M. N., Gaskett, A. C., Lord, J. M., & Pattemore, D. E. (2022). A global review demonstrating the importance of nocturnal pollinators for crop plants. Journal of Applied Ecology, 59(12), 2890–2901. https://doi.org/10.1111/1365-2664.14284 
4. Macgregor, C. J., Pocock, M. J. O., Fox, R., & Evans, D. M. (2014). Pollination by nocturnal Lepidoptera, and the effects of light pollution: a review. Ecological Entomology, 40(3), 187–198. https://doi.org/10.1111/een.12174 
5. Fox, R., Oliver, T. H., Harrower, C., Parsons, M. S., Thomas, C. D., & Roy, D. B. (2014). Long‐term changes to the frequency of occurrence of British moths are consistent with opposing and synergistic effects of climate and land‐use changes. Journal of Applied Ecology, 51(4), 949–957. https://doi.org/10.1111/1365-2664.12256 
6. Falchi, F., Cinzano, P., Duriscoe, D., Kyba, C. C. M., Elvidge, C. D., Baugh, K., Portnov, B. A., Rybnikova, N. A., & Furgoni, R. (2016). The new world atlas of artificial night sky brightness. Science Advances, 2(6). https://doi.org/10.1126/sciadv.1600377 
7. Fabian, S. T., Sondhi, Y., Allen, P. E., Theobald, J. C., & Lin, H. (2024). Why flying insects gather at artificial light. Nature Communications, 15(1). https://doi.org/10.1038/s41467-024-44785-3 

Featured image: Yellow Shell Moth in Le Ménil-Scelleur, France on September 9, 2010 by iNaturalist user sylvainm_53