When honeybees go foraging in gardens or forests, the world is their bouquet. But sometimes we need them to forage and pollinate vast fields of a single commercial crop such as sunflowers, so how can we entice them to selectively pollinate a single crop? Researchers Walter Farina, Andrés Arenas and colleagues from Universidad de Buenos Aires, Argentina, wanted to find out whether they could train honeybees to pollinate a crop of sunflowers.
The scent of a sunflower is a cocktail of about 200 compounds. However, bees may only respond to a few of the compounds to locate a particular flower. Knowing this, the team developed two synthetic blends including just three compounds, each mimicking the natural scent of sunflowers, and tested whether bees respond to them as they do to natural sunflowers. For this, they trained young forager bees to associate the synthetic sunflower scents with sugar solution reward – a bit like Pavlov's dogs learned to associate a ringing bell with the arrival of food – and tested whether the bees could distinguish the fake scent from genuine sunflower scent and that of another natural flower, jasmine. Interestingly, the trained bees could not discriminate the synthetic sunflower scents from natural sunflower scent: three scent components were as good as the real thing. However, they could discriminate the synthetic scents from jasmine scent, as expected. This helped the team to choose a sunflower-mimic scent that could help the bees to establish a long-term memory (lasting at least 4 days), which could help them to learn to visit sunflowers. But were these sunflower-like sweet memories sufficient to entice the bees to prefer sunflowers over other flowers?
When honeybee foragers find food, they convey the distance and direction of the food source to their nestmates by performing elaborate waggle dances when they return to the hive. To test whether the bees that were fed synthetic sunflower scent-infused sugar solution would bias their foraging toward a sunflower crop, the team decoded the bees’ waggle dances by filming inside the hive. The team found that those colonies that had been fed with sugar solution laced with sunflower-mimic scent advertised more and earlier for the sunflower plot than colonies that had been fed sugar solution with the scent of jasmine. Also, the former colonies collected more sunflower pollen and increased their foraging activity, with more hive residents visiting nearby sunflower patches and larger numbers of well-laden foragers returning home. The bees that were fed sugar solution with synthetic sunflower scent found the sunflower plots more alluring.
The team then used an additional test involving colour powder scattered on cotton at the hive entrance to mark the outgoing bees to reveal the foraging preferences of colonies raised on sunflower- or jasmine-mimicking sugar solutions. Collecting over 300 bees at the sunflower plots and on other nearby wild blooms, the team found that the bees trained with the sunflower-mimic scent visited sunflowers more often than other flowers near the hives. And when the team checked to find out whether the trained bees’ fascination with sunflowers translated into improved sunflower seed yields, they were delighted to see that the flowers visited by the trained bees produced up to 57% more seed.
Floral scents learned inside bee hives can thus help increase pollination efficiency and crop yield. Notably, this method works without compromising the environment, unlike the alternatives that involve spraying pheromones on the flowers to attract honeybee foragers. Just by training the bees with relevant information about your crop, you can help them offer precise pollination services.