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Let's talk about bumblebees. You can't even imagine what they were willing to do to get some pollen. By Daria Spasskaya meduza.io4 min View Original

Among all the insects in the spring, bumblebees are one of the first to come across. Unlike other pollinators, they are quite cold-loving, due to the peculiarities of thermoregulation and a thick cover of hairs on the body. Therefore, bumblebees are able to climb far to the north, where they make a major contribution to plant pollination. However, biologists have found that this is not their only useful function - it seems that bumblebees can influence the life cycle of plants around their nest, accelerating the appearance of flowers on them.

Like bees, their close relatives, bumblebees are social insects. But, unlike bees, every spring after hibernation, bumblebees organize a new colony. For its development, resources are needed, that is, flowers on which bumblebees collect nectar and pollen. If the end of winter does not coincide with the beginning of flowering of plants in the vicinity of the colony, it will not survive. Apparently, to avoid this, bumblebees have learned to literally accelerate the “onset of spring” around them, suggested scientists from the environmental department of the Technical School of Zurich.

After observing bumblebees for several years, scientists noticed that they sometimes make holes in leaves for an unknown purpose. To find out how leaf perforation would affect plants, the researchers conducted an experiment in a greenhouse. Tomato and mustard plants, which were not yet ready to bloom, were left alone with bumblebees of the species Bombus terrestris , and the latter were allowed to perforate the leaves. The scientists also created two control groups: one of them was left untouched, and in the other, holes were cut out in the leaves of plants using a scalpel, similar to those gnawed by bumblebees.

It turned out that bumblebees begin to gnaw holes in leaves only if they are not fed pollen, which serves as their main source of protein. At first glance, it might seem that the hungry bumblebees simply wanted to eat some leaves. But scientists say the insects didn't do anything with the cut-out pieces—they didn't eat them or take them back to the nest. In addition, bumblebees usually do not eat leaves, and in order to drink plant juices, they spent too little time on the leaf - creating each hole took them no more than a few seconds.

By observing plants in a greenhouse, scientists found that specimens chewed by bumblebees bloom earlier than control plants. For example, tomatoes “treated” by bumblebees bloomed a whole month earlier than those that were not touched by bumblebees, and mustard - two weeks earlier. The holes cut with a scalpel also speeded up flowering a little, but not to the same extent as the bumblebee perforation - by only five days.

To confirm what they saw in the lab, the researchers observed bumblebees living on the roof of a university campus over two seasons in the spring and summer. Scientists wanted to find out whether bumblebees would stop damaging leaves once flowers appeared near the nest. It turned out that with the appearance of flowers, bumblebees almost stop gardening. With this observation, scientists confirmed that such behavior in bumblebees is explained precisely by a lack of pollen. In a “field” experiment, scientists also discovered that honey bees are not interested in non-flowering plants; similar behavior is more typical of bumblebees, of several species.

However, what remains unclear in this story is the mechanism by which bumblebees accelerate plant flowering. It is known that plants also experience stress, and factors such as leaf damage, drought, cold weather and others can accelerate flowering due to internal hormonal regulation. But in the experiment described, artificial cuts did not accelerate the appearance of flowers as much as the work of bumblebees. It is possible that during the perforation process, bumblebees introduce some special substances into the leaves, but this remains to be determined.

It is also not known whether bumblebees have always bitten plants to speed up their flowering, or whether this is an example of adaptive behavior that has developed over the past decades. The fact is that the discrepancy between the regimes of bumblebees and plants is becoming threatening for insects - as a result of climate change, bumblebees began to wake up earlier, and the appearance of flowers, which depends mostly on the length of daylight hours and not temperature, has hardly changed.

Do bumblebees know that by biting leaves they speed up the appearance of flowers? Bumblebees have repeatedly demonstrated their intelligence in laboratory experiments. Unlike “domestic” bees, their colonies are less structured and social roles are not so rigidly predetermined. Knowledge sharing appears to be common in bumblebee communities. For example, in 2016, scientists talked about how they taught bumblebees to pull out treats by a string, and trained bumblebees taught their comrades to do this. In 2017, bumblebees were taught to play an analogue of pinball - rolling a ball into a hole, also in exchange for a treat, and again they were able to learn this from each other. Apparently, bumblebees have a good enough spatial memory to remember which plants they have "processed".

However, scientists still doubt that insects are able to predict the harvest a month in advance. In addition, workers in nature rarely live more than a month, so their agrotechnical skills are most likely a consequence of the mutual adaptive evolution of plants and pollinators.