The Importance of Multispecies Perspectives on Air Pollution

A Hindrance to Scent-Based Navigation

Discourse regarding health implications of air pollution usually takes place from an anthropocentric perspective. However, recent research has begun explicating the implications of air pollution for other species, plants and animals alike. One important group to hone in on while developing policies and regulations regarding air pollution is pollinators, owing to how they form the backbone of the global food system, with about 75% of global crop production reliant on them [1].

Previously, it has been showcased that pollinators rely on the floral odours emitted by plants- comprising of volatile organic compounds (VOCs)- to navigate through their pollination routes[2] . Unfortunately, exposure to atmospheric pollutants such as nitrogen oxides (NOx) and ozone (O3) can impede this system of navigation, either by directly reacting with the VOCs and affecting their composition [3] or through masking the floral scent [4].

Ryalls et al (2022) examined this effect beyond the lab by utilising a free air fumigation set-up in the field to demonstrate the detrimental effects of traffic associated air pollution on pollinators. Accordingly, they exposed pollinators to different experimental conditions such as to NOx containing car exhaust and O3, both separately and in combination. They found that in comparison to a control group, the experimental number of pollinators per flower and number of flowers visited decreased by more than 62% and 83% respectively[5]. This study is important since it provides in-situ evidence to substantiate the results of previous research which utilised modelling techniques to predict effect of air pollution on pollinators. Importantly, Ryalls et al (2022) had exposed the pollinators to levels of car exhaust currently deemed by the Environmental Protection Agency as “safe for the environment”. This surely calls raises the question of safe for who? It appears that the wellbeing of species beyond humans is seldom accounted for while developing environmental health regulations.

A Sticky Situation: Adherence of Particulate Matter on Pollinator Bodies

However, the adverse effects of air pollution on pollinators are not merely limited to an obstruction of their dependency on VOC for navigation. Instead, studies showcase how exposure to air pollution also leads to an accumulation of particulate matter on the bodies of pollinators themselves [6]. Under normal circumstances, the electrostatic charges on pollinator bodies help pollen stick to them as they feed on flower nectar. Capitani et al (2021) demonstrated how this very static charge also enables harmful particulate matter to adhere to pollinator bodies. In fact, they illustrated how the results yielded from electron microscopy of the bodies of pollinators in heavily polluted areas was indicative of the area’s traffic, high-combustion processes, and agricultural processes [7]. The authors go on to suggest that pollinators thereby provide one method of monitoring the air quality of a given area. But what effect does this particulate matter have on the pollinators themselves?

The specific impact of exposure to air pollution on the morphology and physiology of pollinators was illustrated by a comprehensive study undertaken by Thimmegowda et al (2020). In terms of morphology, they found significantly higher levels of respirable suspended particulate matter (RSPM) accumulated on the wings, legs, and antennae of Giant Asian honey bees in polluted areas [8]. Perhaps even more concerning were the results regarding the physiology of the bees, since these highlighted how high levels of pollution have adverse impacts on the heart rate (video below) as well as on the gene expression of stress-associated genes in bees.

As air pollution worsens, its environmental and health impact on non-human species is gaining more traction. Ultimately, it is evident that tackling environmental issues requires a multispecies perspective, one which goes beyond solely looking after human interests.

References

[1] Shivanna, K. R. (2022). The Plight of Bees and Other Pollinators, and its Consequences on Crop Productivity. Resonance, 27(5), 785–799. https://doi.org/10.1007/s12045-022-1372-8

[2] Leonard, R. J., Vergoz, V., Proschogo, N., McArthur, C., & Hochuli, D. F. (2018). Petrol exhaust pollution impairs honey bee learning and memory. Oikos, 128(2), 264–273. https://doi.org/10.1111/oik.05405

[3] Jamieson, M. A., Burkle, L. A., Manson, J. S., Runyon, J. B., Trowbridge, A. M., & Zientek, J. (2017). Global change effects on plant–insect interactions: the role of phytochemistry. Current Opinion in Insect Science, 23, 70–80. https://doi.org/10.1016/j.cois.2017.07.009

[4] Riffell, J. A., Shlizerman, E., Sanders, E., Abrell, L., Medina, B., Hinterwirth, A. J., & Kutz, J. N. (2014). Flower discrimination by pollinators in a dynamic chemical environment. Science, 344(6191), 1515–1518. https://doi.org/10.1126/science.1251041

[5] Ryalls, J. M. W., Langford, B., Mullinger, N. J., Bromfield, L. M., Nemitz, E., Pfrang, C., & Girling, R. D. (2022). Anthropogenic air pollutants reduce insect-mediated pollination services. Environmental Pollution, 297, 118847. https://doi.org/10.1016/j.envpol.2022.118847

[6] Capitani, G., Papa, G., Pellecchia, M., & Negri, I. (2021). Disentangling multiple PM emission sources in the Po Valley (Italy) using honey bees. Heliyon, 7(2), e06194. https://doi.org/10.1016/j.heliyon.2021.e06194

[7] Capitani, G., Papa, G., Pellecchia, M., & Negri, I. (2021). Disentangling multiple PM emission sources in the Po Valley (Italy) using honey bees. Heliyon, 7(2), e06194. https://doi.org/10.1016/j.heliyon.2021.e06194

[8] Thimmegowda, G. G., Mullen, S., Sottilare, K., Sharma, A., Mohanta, S. S., Brockmann, A., Dhandapany, P. S., & Olsson, S. B. (2020). A field-based quantitative analysis of sublethal effects of air pollution on pollinators. Proceedings of the National Academy of Sciences, 117(34), 20653–20661. https://doi.org/10.1073/pnas.2009074117