Shadowy world of nocturnal moth pollinators

Most flowering plants need animals to facilitate pollination and, globally, most studies have focused on daytime insect – honeybees are the best known – and bird pollinators. Other critters playing a hand include bats, butterflies, beetles, flies and small mammals.

The role of moths, in contrast, hasn’t attracted much attention.

“There’s a lot we don’t know about moths, although this is beginning to change and we’re beginning to understand more about their importance,” says New Zealand Institute for Plant & Food Research botanist Max Buxton, lead author of a soon-to-be-published paper in the New Zealand Journal of Ecology. “As you can imagine, studying anything at night is made even more difficult by the lack of light. This makes logistics and health and safety considerations a challenge and even more so when the plants are in remote and isolated areas.”

And it’s not just about whether-or-not – it’s also about how. So Buxton and his colleagues, in what they believe to be a first-of-its-kind experiment, used a fluorescent pollen-tracker powder in the lab to test whether moths could effectively transfer pollen between certain flowers, including those of the tea-tree renowned for its honey and oil called mānuka (Leptospermum scoparium), for which moths were thought to be a pollinator.

Read more: Ultra-violet confirms “Darwin’s moths”

“Honeybees, bumblebees, and native bees are considered to be important pollinators for this species and are often seen visiting the flowers in large numbers,” says Buxton. “Various flies are also known to visit the flowers. Less well known was that moths also visit the flowers at night, as was [first] reported in [1978].”

The idea of using pollen tracker came from the research supervisor, and Buxton’s co-author, Associate Professor Janice Lord of the University of Otago, and the innovative experiment’s design was as “a bit of an accident”.

“The original plan was to observe the moth species and then remove them after one visit to a flower,” says Buxton. “Many hours were spent watching moths under red light (which moths can’t perceive) but in each of these observation periods no moths were seen to move.

“After one of these failed attempts I ended up just going home thinking ‘I’ll clean this up tomorrow’ and ended up leaving the moths in the cages overnight. The following morning, I was surprised to see moths and pollen tracker had been moved around the cage, and so the experimental design changed.”

The two endemic NZ moth species studied – the nectar-feeder Ichneutica plena and Wiseana spp (which as adults have no functioning mouthparts and weren’t expected to be floral visitors) – moved the pollen-tracker powder after visiting the mānuka, offering evidence that moths could be mānuka pollinators.

Buxton says he expected to see some transferring of the pollen tracker, but that he didn’t expect either species to transfer tracker between the flowers at the rates observed. “I was particularly surprised to see the non-feeding moth species transfer the tracker at the rate it did, I expected this value to be considerably lower.”

He says it’s still too early to know how important nocturnal pollination could be to mānuka and Pimelea prostrata, the other plant species in the study, but it does show that moths “are likely of some importance”.

“What we need to do now is take what we’ve learnt from this study (that moths are able to transfer pollen between the flowers in cages) and look at this in the real world,” he says. “We know that moths visit the flowers of these plant species, but [we’d like to know] how these visits result in seeds being produced through pollination, or what proportion of pollination is achieved through moths versus other species.”

And the wider story, the contribution that moths are making – after hours – to pollination on a NZ national and even global scale? Buxton for one is a believer. Nocturnal pollinators are the subject of his PhD, and he’s assessing the importance of them, particularly moths, in the pollination of more NZ native plant species and crops.

“Nocturnal pollination is more important than is currently considered, both in New Zealand and globally, but it’s yet too early to know just how important it is because of the lack of research on the topic,” he says.

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