Nectar is renowned as nature’s sweetest brew, but to do its job it needs a touch of bitterness too.
Nectar feeders such as moths and hummingbirds are attracted by the sweetness, but it’s not in the plant’s interest for them to stay too long. If they do, and drink all the nectar in one go, there’ll be none left for subsequent visitors, leaving fewer opportunities for the plants to spread their pollen. “The trick is to attract the greatest number of pollinators for the least amount of nectar,” says Ian Baldwin of the Max Planck Institute for Chemical Ecology in Jena, Germany.
To test the idea that plants balance sweetness and bitterness Baldwin, working with colleague Danny Kessler, spiked flowers of the tobacco relative Nicotiana attenuata with extra nicotine, a repellent naturally present in nectar. Sure enough, the extra nicotine made pollinator birds and moths cut short their visits, allowing the nicotine-treated plants to receive twice the number of visits per hour and increase the exchange of pollen (The Plant Journal, vol 49, p 840).
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Baldwin and Kessler then bred plants that couldn’t make nicotine. These plants lost up to 70 per cent more nectar per night than ordinary plants, showing that sweet nectar does indeed tempt pollinators to “drain the pot”.
