They often appear beautiful to us - but what is the actual purpose of drawings on petals? A study with bumblebees shows that plants can use the visual elements to help their pollinators make particularly efficient and thus energy-saving visits. The researchers report that the insects needed up to 30 percent less time for the entire interaction compared to monochromatic versions.
It is a fascinating partnership between living beings, with enormous importance for nature: In the course of evolution, certain plants have developed ingenious structures designed to interact with insects. Flowers provide food for these animals through nectar and in return the visitors serve as messengers for the plants. Bumblebees and co take pollen with them when they search for food and then transport it to other flowers to ensure pollination and seed formation. It is therefore in the “interests” of the plants to make this system as attractive and comfortable as possible for the pollinators. For this reason, flowers are often striking in color and structurally adapted to the desired visitors.
"Juice marks" in sight
These botanical concepts often include eye-catching drawings on the petals. Stripe patterns are particularly common in the mallow family or petunias, for example. In biology, such conspicuous structures are called sap marks. Because it has long been assumed that they are intended to support pollinating insects in their search for nectar. While it is known that flower patterns play an important role in flower selection, other mechanisms have remained unclear. Researchers at the Julius-Maximilians-Universität Würzburg have now investigated to what extent such drawings can improve the efficiency of insects when they search for food.
The biologists carried out experiments with ground bees (Bombus terrestris) and artificial flowers. Some of the subjects, always provided with a nectar source, had a uniform coloration, others had a single horizontal stripe, and in the third variant, stripes formed a tapered pattern similar to that found in some flowers. Using video tracking, the scientists recorded in detail how the experimental bumblebees reacted to these differently designed food sources.
More efficient flower visits
The evaluation of the test runs showed: In contrast to the single-colored artificial flowers with only one line, the bumblebees needed significantly less time to visit the versions with the simulated sap marks: from approach to finding the nectar to departure - the duration that The researchers found that drawing reduced the time required for the entire interaction by up to 30 percent. It is thus characterized by increased efficiency. As a result, the insects can apparently save energy during the strenuous search for food, which benefits them and ultimately also the plants.
In detail, the behavioral analyzes of the bumblebees revealed: Surprisingly, the flower patterns apparently do not shorten the actual search for the nectar source on the flower, as previously assumed. Because it turned out that the bumblebees find the nectar no faster after landing on a striped flower than on a version without a pattern. Instead, the flower patterns apparently ensure a more efficient approach and lead to a more strategically favorable landing position, the observations suggest.
According to the scientists, they act like markings on a runway and help the bumblebees to coordinate their approach. According to them, they could also have a similar function on departure. After all, the insects lingered on patterned blossoms for significantly less time than on single-colored blossoms, even after collecting nectar. "Bumblebees very often run to the edge of the petals to take off," explains senior author Johannes Spaethe. They may find this starting place faster if they can orientate themselves on a pattern, so the assumption.
As the researchers announce, they will now continue to investigate the visual effects of flowers and their effects on pollinators. They are now also planning to investigate how the iridescent luster effects that characterize some flowers influence the interaction with pollinating insects.
Source: Julius Maximilian University of Würzburg, specialist article: Functional Ecology, doi: 10.1111/1365-2435.14262