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Are all plant pollinators as busy as a bee?

There’s an article recently published in Psyche, that might be of interest to botanists Busy Bees: Variation in Insect Flower-Visiting Rates across Multiple Plant Species. It’s not a surprise that there are differences in visitations between species, there was a recent special issue of Pollinator-Driven Speciation in Annals of Botany that would have looked very different if there was no variation. However, what Couvillon et al. do is look at it from the insect point of view. It gives a chance to see how generalists work instead of specialised adaptations of pollinators and plants.

Osmia lignaria on a bramble
Blink and you’ll miss it? Osmia lignaria on a bramble. Photo: Eileen Delhi / Flickr.

The study looked at visits to five plants, bramble (Rubus fruticosus), California lilac (Ceanothus spp.), marjoram (Origanum vulgare), ragwort (Jacobaea vulgaris), and ivy (Hedera helix and H. hibernica). It’s a range of plants, but their common features are that they attract insects, and they are native to the UK, except California lilac, which is grown as an ornamental plant.

The diversity proved to be a small problem when they decided to measure flower visits. What exactly is a flower visit? The authors note that it’s easy to spot a visit to a bramble flower, the flowers are large. But when the flowers are composites or arranged in inflorescences, so you have bundles of small flowers together, it becomes impossible. So for these plants a ‘flower visit’ was a visit to an inflorescence, but it was measured the same way for all insects visiting the same plant.

Insect forage speeds, with bumble bees fastest.
Insect pollinator forage speed by Couvillon et al. See original paper for full details.

The results were that bumble bees and honey bees were the fastest foragers, with beetles the slowest. This was not a surprise in itself, Couvillon et al. point out Chaucer invented the phrase ‘busy as bees’ in the 14th century. The non-Apidae bees follow the bumble and honey bees, but they are not all the same.

Osmia bees significantly out-perform other non-Apidae bees.
Non-Apidae bee visits compared to Honey bees by Couvillon et al. See original paper for full details.

Osmia bees, commonly called Mason bees in the UK, are solitary wild bees. but they get on with neighbours. They have been suggested as alternatives to honey bees for pollination of crops.

What I found interesting was the brief discussion of why Apidae bees are usually much faster than other insects. One suggestion Couvillon et al. make is that the Apidae bees are there purely for the food, while other insects might collect food while performing other tasks, like laying eggs. It highlights the importance of timing in plant-insect interactions, beyond broad sweeps of the season.

What might also produce interesting result would be a comparison with foraging over native and exotic plants, similar to the Hanley et al. study of native and exotic plants in gardens from Annals of Botany last year, but from the insect perspective. It might help add a little more light on what is happening to bees in urban environments.

You can pick up Couvillon et al.‘s paper with Open access from Psyche.

Couvillon MJ, Walter CM, Blows EM, Czaczkes TJ, Alton KL, Ratnieks FLW. 2015. Busy Bees: Variation in Insect Flower-Visiting Rates across Multiple Plant Species. Psyche: A Journal of Entomology 2015: 1–7.
http://dx.doi.org/10.1155/2015/134630

Hanley ME, Awbi AJ, Franco M. 2014. Going native? Flower use by bumblebees in English urban gardens. Annals of Botany 113: 799–806.
http://dx.doi.org/10.1093/aob/mcu006

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