If hungry bumblebees find no flowers, they take a rabid measure, researchers report: the insects bite plants in the vicinity of their stick. The message is obviously: “Go ahead, start blooming!” Because the plants so trailed produce flowers up to a month earlier than comparative specimens. This phenomenon probably developed for the timing of the plants with their pollinators, the researchers explain.
They growl comfortably from flower to flower – the bumblebees are on the move early in the year to obtain pollen and nectar for growing their brood. The plants offer them this food generously, because the insects do an important service for them: They carry the pollen from one flower to the next and thus ensure fertilization and seed development. It is an ancient partnership between flowering plants and specialized insects such as bumblebees. It is important for both that supply and demand are well timed. Because when the flowers open, the pollinators should be there – and vice versa, the insects need good nutrition to develop optimally.
If the climate capers in spring, this vote can get out of hand. Because some plants use the length of the day to develop flowers, but the bumblebees to the temperature, there can be shifts: the insects are active early on and need food – however, the plants limp here when the flowers form. As forecast shows, climate change could now cause such coordination difficulties more and more often. How nature will cope with it is difficult to assess. But as the study by the researchers led by Pashalidou from the Swiss Federal Institute of Technology in Zurich shows, there is apparently a previously unknown communication system between bumblebees and flowering plants that can at least improve the timing of the partners.
Discount request
As the biologists report, the study began with the finding that bumblebees (Bombus terrestris) seemed to attack flowerless plants in their experimental greenhouses: they made small holes in their leaves with their mouthparts. It was reasonable to assume that they absorb plant substances from the leaves. But as the research showed, that was not the case. So the scientists developed another suspicion: the insects may encourage the plants to flower. This seemed possible because plants are known to go into the generative phase after threats such as drought or mechanical damage in order to produce seeds as quickly as possible.
To investigate the suspicion, the researchers carried out comparative experiments. It was found that tomato plants that had been treated by the bumblebees bloomed up to thirty days earlier than control plants without contact with the insects. Mustard plants that were also examined reacted with a flowering time that had been brought forward two weeks. The scientists also tested whether holes in the leaves caused by tweezers also caused the same effect. There was also an early effect – but it was much more pronounced in the bumblebee bite. The researchers therefore suspect that the animals cause an additional stimulus, which leads to the more intensive reaction of the plants.
Bite hungry bumblebees
But is the behavior of the bumblebees really linked to their hunger and lack of food? The researchers also investigated this question in laboratory and field trials. The results showed that the bumblebees only attack the leaves of their potential food suppliers if there are hardly any flowers and therefore little pollen in the vicinity of the stick. The following also applies: the more the animals have to starve, the more holes they cause in the leaves.
In addition to the bumblebee (Bombus terrestris) the scientists also observed the behavior of two other species: they observed in the field how some stone bumblebees (Bombus lapidarius) and white bumblebees (Bombus lucorum) also tampered with the leaves of flowerless plants. This behavior may be widespread among bumblebee representatives. The honey bee, on the other hand, does not seem to be pushing plants to bloom earlier, the researchers write. This may be due to the fact that the bumblebees are particularly dependent on a good pollen supply in spring. In contrast to honeybees, bumblebees build a new colony every year.
As the researchers emphasize, some questions about this behavior remain unanswered. Through further investigations, they now want to uncover the background and the ecological significance of the concept in more detail. “One could interpret the new findings in an encouraging way,” writes Lars Chittka of the Queen Mary University of London in a comment on the study. “Due to the behavioral adjustments of the flower visitors, the pollination system may have more plasticity and resistance to climate change than previously thought,” said the scientist.