Several recent studies have drawn attention to the work of bumblebees in horticulture.

In February of this year the ABC ran an article to the title: “Bumblebees can create mental imagery, a ‘building block of consciousness,’ study suggests.” The article went on to say: “Humans are one of very few animals known to be able to recognise objects across senses. For instance, if we know what a jar of honey looks like we could probably find it by touch alone from the top shelf of the pantry.

Scientists think this ability – called cross-modal object recognition – exists at least partly because we are able to imagine the object in our brain, a skill that is a “building block” of consciousness.

But now a team of scientists believe they have evidence bumblebees can also create mental imagery, they report in the journal Science. The tiny insects are able to recognise objects by sight that they’ve only previously felt, and vice versa.”

A different set of researchers conducted behavioural tests on bumblebees and wrote in Science magazine: “Bumble bees have already proven themselves remarkable animals. They possess complex navigational skills, rudimentary culture, and emotions. They can even use tools. Bumble bees may have small brains, but that doesn’t mean they’re not inventive. A new study shows that the insects can innovate to solve complex problems, quickly figuring out a better way to get a sugar reward.”

“Most importantly for the study’s researchers, ‘It puts the final nail in the coffin of the idea that small brains constrain insects’ cognitive abilities,’ says co-author Lars Chittka, a behavioural ecologist.”

Another article appeared a number of years ago in Nature, describing how bumblebees sense electric fields in flowers.

“As they zero in on their sugary reward, foraging bumblebees follow an invisible clue: electric fields. Although some animals, including sharks, are known to have an electric sense, this is the first time the ability has been documented in insects.

Pollinating insects take in a large number of sensory cues, from colours and fragrances to petal textures and air humidity. Being able to judge which flowers will provide the most nectar, and which have already been plundered by other pollinators, helps them to use their energy more efficiently.

It has long been known that bumblebees build up a positive electrical charge as they rapidly flap their wings; when they land on flowers, this charge helps pollen to stick to their hairs. Daniel Robert, a biologist at the University of Bristol, UK, knew that such electrical interactions would temporarily change the electrical status of the flowers—but he did not know whether bumblebees were picking up on this.”

In their summary, the researchers wrote: “Insects use several senses to forage, detecting floral cues such as colour, shape, pattern, and volatiles. We report a formerly unappreciated sensory modality in bumblebees—detection of floral electric fields. These fields act as floral cues, which are affected by the visit of naturally charged bees. Like visual cues, floral electric fields exhibit variations in pattern and structure, which can be discriminated by bumblebees. We also show that such electric field information contributes to the complex array of floral cues that together improve a pollinator’s memory of floral rewards. Because floral electric fields can change within seconds, this sensory modality may facilitate rapid and dynamic communication between flowers and their pollinators.”

“We think bumblebees are using this ability to perceive electrical fields to determine if flowers were recently visited by other bumblebees and are therefore worth visiting,” says Robert.

A later study in the Proceedings of the National Academy of Sciences described how the bees sensed these electric fields.

“We used a laser beam that could measure small motions of an antenna or a hair, and that’s how we measured how much the air and the antenna moved in response to an electric field,” says Sutton. They also stuck a very fine electrode wire into the nerve at the socket of the bottom of a hair to record the activity of nerve cells there.

“They’ve got these really fuzzy hairs all over their body, and when they approach something with an electric field, that electric field will bend the hairs on their body,” says Sutton. And that bending generates a nerve signal.

The results suggest that bumblebees can sense an electric field produced by a flower that’s up to 55cms away. But that’s under ideal conditions in the lab – Sutton says that 10cms is more likely in the real world.

Over 30 years ago New Zealand Geographic ran a wonderfully descriptive article on the bumblebee’s virtues as a tireless and effective pollinator. Here are some extracts from that article:

“When we think of flowers being pollinated, we generally think of honeybees, but in many ways bumblebees are superior pollinators. The larger, furrier bodies of bumblebees collect more pollen from the stamens (male flower parts) and make better contact with the pistils (female flower parts) than do honeybees or other insects.

Honeybees and native bees are often too small or selective to effectively pollinate some flowers. Flowers that provide only pollen, such as tomatoes and kiwifruit, are generally not attractive to honeybees, but bumblebees will happily work these blooms if the hive is supplied with a sugar solution to compensate for the lack of nectar.

Tongue length is also important to the bumblebee’s success. Honeybees have short tongues compared with those of bumblebees and are not interested in working tubular flowers (such as broad beans and red clover) because they usually cannot reach the nectar at the bottom of the flower.

The length of the bumblebee tongue is easily appreciated if you have the patience to quietly sit and observe bumblebees working. Occasionally, when collecting from large vertical inflorescences such as foxgloves or delphiniums, the bumblebee will not retract its proboscis between flowers, and resembles a tiny, flying, striped elephant.

One situation where bumblebees have demonstrated their clear superiority over honeybees is in the glasshouse – especially tomato glasshouses.

But why use bumblebees? Why not honeybees? For the simple reason that honeybees refuse to work tomatoes. As well as having no nectar, tomato flowers have their pollen inside the anthers, rather than clumped on the tips like sherbet. Honeybees are not boisterous enough in their gathering to dislodge the pollen.

Bumblebees, on the other hand, buzz the flowers vigorously, and are rewarded with a shower of pollen falling on to their bodies. To a honeybee, a tomato flower is about as interesting as a used bus ticket!”

“When it comes to work, bumblebees are the draught horses of the bee world. In a tomato glasshouse, a single bumblebee is capable of pollinating 450 flowers per hour, taking an average of eight seconds to harvest pollen from one bloom before travelling to the next one.

Bumblebees fly and forage in misty, rainy weather, and at temperatures just a few degrees above freezing – conditions in which a honeybee won’t budge from home. Bumblebees can fly in adverse circumstances because, unlike most insects, they are able to maintain their flight muscles at a more or less constant 34-40°C – well above air temperature.

The muscles of most terrestrial animals don’t work properly if they’re cold. To overcome this problem, furry and feathered animals maintain a constant body temperature (we call this being “warm-blooded”), while most insects and reptiles heat their muscles up by sitting in the sun or vibrating their wings.

Bumblebees can decouple their wings from the flight muscles that drive them, and warm up these muscles simply by shivering. Using this approach, a bumblebee can raise the temperature of its thorax from 24°C to 37°C in one minute. Bumblebees are also clad with a fine fuzz, which plays a major role in conserving body heat. These peculiarities are a heritage of the bumblebee’s geographic heartlands: cool temperate latitudes of the northern hemisphere, with a few species even extending beyond the Arctic Circle.

Although airborne or foraging bumblebees maintain a nearly constant thoracic temperature, the temperature of the abdomen (which has no flight muscles) can be varied by the bee to suit its needs. On a cold day, the bumblebee uses a counter current heat exchange arrangement in its blood vessels to conserve heat in the thorax, allowing the abdomen to cool close to ambient temperature. On a hot summer’s day, when extensive flying threatens to cause overheating in the thorax (insects can’t sweat, although bumblebees can evaporate nectar off their tongues to cool down), the heat exchanger in the bee’s waist is bypassed, so heat can be dissipated from the abdomen. When they are not flying, bumblebees allow their bodies to cool down to ambient, to save energy.”

(To be continued)