This unusual donkey orchid uses UV light to trick bees into thinking it has food

If you’ve ever compared a frozen pizza to the photo on the box, you know the feeling of being fooled by an attractive appearance.

In our latest study we show that animals – in this case, bees – are also often tricked into making wrong decisions, which explains a lot about how cognitive gaps are used in nature.

When Charles Darwin was exploring the theory of evolution 150 years ago, he looked at the interaction between flowering plants and animals that eat food to collect nectar.

This helped to confirm that flowers have ways to make it easier to find pollinators, making it better for the animal that gets the “reward” of food from them. At the same time, it means that plants receive seeds and can reproduce.

Another perplexing problem is that flowering plants that reproduce by pollination have no reward – the animal does not get nectar when it visits the flower. This is true of other orchids, however these flowers are still visited by pollinators and thrive in nature.

Wrong information

With the benefit of the latest scientific equipment such as color spectrophotometers, digital ultraviolet (UV) photography and computerized visualization of the way bees see the world, our international team set out to understand why other orchids had spectacular flower displays.

The species we chose were the winter donkey orchid (Winter season), common in Western Australia. This non-rewarding, food-deceiving plant blooms at the same time as the hearty pea plants.Daviess).

Dandelion winter flower (left) and bitter pea.
Cal Wood/iNaturalist; caitlind164/iNaturalistCC BY

Therefore, native Trichocolites Bees often seem to mistake orchids and legume plants for the orchid to pollinate.

We measured flower color signals from both plants, revealing that the main part of the information perceived by bees was in the short UV wavelength region of the spectrum.

This made sense – while our vision sees blue, green and red light rays as primary colors, bees can see UV light but have no channel to see primary red .

Using computer-aided bee recognition techniques, we saw mimic orchids and native pea plants that actually looked like bees in color.

A chart showing two pictures of flowers, a larger yellow one and a smaller one, with a graph next to them
The shape and color of orchid flowers (top row) and natural pea flower (bottom row) shown in the field, as individual flowers, and in spectral measurements.
Sscacabarozzi et al., 2023, Given an author

Putting a UV light on the flowers

However, what was surprising was that the non-rewarding orchids – the ones that were contaminated with deception – actually had more obvious advertisements for the bees to see.

For example, the large display of flowers of outdoor flowers was very large in orchids, and they also produced a strong UV color signal.

To understand whether such a display was important for health, we followed field experiments with plants. We used a special UV blocking solution to remove the strong rays of the sun from half of the orchid species, while the other half kept its natural appearance.

A row of colorful and purple floral images next to a two-dimensional chart
UV photos of orchid flowers (top left panel) in natural condition and with a UV blocking screen installed. The middle panels show false-color photographs of the appearance of flowers to bees, and the right-hand panel shows a computer model of how the bee’s vision perceives the colors of flowers.
Sscacabarozzi et al., 2023, Given an author

At the end of the field season, several months later, we were able to measure which plants were successfully pollinated by bees, revealing that strong UV signals played an important role in promoting pollination of orchids.

The second interesting thing that was found in the field experiments was that the distance between the pea flowers and their copycat orchids was a big reason for the success of the orchid deception strategy.

If the orchids with strong UV signals were close – a meter or two – to the red flowers of the natural pea, the deception was less effective and few orchids were contaminated. However, if the deceptive maiden flowers were eight meters away from the rewarding variety, this produced the highest pollination success.

Why deception works

It appears about eight meters away which is important because of the way the bee’s brain processes color. When bees see a pair of colors close together, they can scan them at the same time. This leads to very accurate color perception. A similar process occurs in the human brain – we also have to see colors simultaneously.

However, to perceive color stimuli in an interval, the brain must remember the first color, evaluate the second color, and make a mental calculation about whether the two samples are the same. .

Neither bees’ brains, nor ours, can match consecutive colors. That’s why when we buy paint for a repair job we take a sample to find the perfect match, rather than trying to remember what we thought the color should look like.

Deceptive flowers succeed by exploiting this gap in the understanding of how the brain is supposed to encode information while bees need to fly several meters to find more food.

By using the strategy of “look at me” (in fact, advertising is better than other plants) it is possible to live in nature without giving a food reward to parasites. To do this, the plants need to be far away from the plants they are mimicking. It’s not too close and not too far, and success is guaranteed.

Read more: ‘Like finding life on Mars’: why the subterranean orchid is Australia’s strangest flower

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