Sphinx moth nectaring on Brazilian vervain
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Permanently photo-postponed pollination (possibly…)

In a world where we might think that bees do all of the plant pollinating, we shouldn’t discount ‘the importance of moths as pollinators for a diverse range of plant species in ecosystems worldwide and, hence, their role in ecosystem functioning’.

Sex is all about timing. Especially for flowering plants, which usually flower only for limited periods in response to various environmental cues. This phase, which is an essential preparatory stage to reproduction, is therefore not a 24-7, 52 weeks a year activity for angiosperms – as it can appear to be for some organisms. It’s therefore all the more important to ensure that pollination happens when it’s supposed to. And, for many plants, that means not only that flowers must be pollen-producing and stigma-receptive, but also that pollinating agents must be about and active at the same time.

Sphinx moth nectaring on Brazilian vervain
Sphinx moth nectaring on Brazilian vervain. Image: Pollinator / Wikipedia.

Pollination is a mutually-rewarding phenomenon that needs two players – plant and pollinator; what if the plant plays its part, but the pollinator is thwarted in its role? In her infinite wisdom Mother Nature decreed that certain plant species should be pollinated by moths, at night. And that usually means in darkness (moonlight and starlight are permitted). For most of evolutionary history it has been sufficiently dark at night-time for moths to go about their plant-pollinating tasks properly.

Unfortunately, as humans – for whatever purposes – illuminate those former darkened hours with all manner of light sources, there may be unintended phytosexual consequences, as revealed by Callum Macgregor et al. Investigating specifically the effects of high-pressure sodium (HPS) street lights on the behaviour of night-flying moths, they discovered that – in lit areas – the insects flew higher (i.e. towards the light* and away from the plants, which they presumably therefore didn’t visit as much), and there was an overall reduction in pollen transport at such sites. Whilst the team are careful to point out that ‘pollen transport or flower visitation do not strictly prove the existence of a pollination interaction … these measures are frequently used as a proxy for insect-pollination; therefore, a reduction in pollen transport may indicate disruption of pollination services.’

Furthermore, other artificial light sources – e.g. light-emitting diodes (LEDs) – are used in the UK (and elsewhere globally), whose potential impacts on moth ecology also need to be examined, along with ‘the cascading effects of lighting on ecosystem functioning’.

In a world where we might think that bees do all of the plant pollinating, we shouldn’t discount ‘the importance of moths as pollinators for a diverse range of plant species in ecosystems worldwide and, hence, their role in ecosystem functioning’. However, with these potential effects on moths, and the plants that rely on them for pollination (not to mention the direct human consequences if those plants are important to our own well-being), surely it’s not beyond the wit of man to achieve a satisfactory solution for all parties. After all, and as a sagacious commentator on matters ecological once said, ‘I know the human being and fish can coexist peacefully’. So, why not the moth and the human being? But, if humans won’t amend matters to suit moths, maybe they can be persuaded to do so to help themselves?

Increasingly, there is evidence that additional illumination when it’s supposed to be dark has health consequences for people, and that the night sky seems to be getting brighter thanks to artificial light sources. So, limit the nocturnal illumination. Do it for the moths. Do it for the plants. Do it for US – and that’s us not necessarily, or just, the USA (because we’re worth it…).

[Ed. – it is to be hoped that the prevalence of artificial illumination doesn’t confuse pollinators of the non-flowering plant Ephedra foemina (a gymnosperm) in Macedonia (Greece) and Dalmatia (Croatia), whose pollen-mediation activities coincide with the full moon in the month of July. One also wonders what effects night-time lightning – such as Hong Kong’s spectacular example – might have on nocturnal pollinators’ behaviour.]

* This well-known propensity of moths is illustrated in the phrase ‘like moths to a flame’, the basis for which seemingly bizarre and potentially self-destructive behaviour is explained here.

Nigel Chaffey

I am a Botanist and former Senior Lecturer in Botany at Bath Spa University (Bath, near Bristol, UK). As News Editor for the Annals of Botany I contributed the monthly Plant Cuttings column to that international plant science journal for almost 10 years. As a freelance plant science communicator I continue to share my Cuttingsesque items - and appraisals of books with a plant focus - with a plant-curious audience at Plant Cuttings [https://plantcuttings.uk] (and formerly at Botany One [https://botany.one/author/nigelchaffey/]). In that guise my main goal is to inform (hopefully, in an educational, and entertaining way) others about plants and plant-people interactions, and thereby improve humankind's botanical literacy. I'm happy to be contacted to discuss potential writing - or talking - projects and opportunities.
[ORCID: 0000-0002-4231-9082]

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