Studies show wild bees are more effective at pollination than you think. Pictured here: Bumblebee (left) and honeybee (right) forage together on sweet cherry flowers.
Photo by Maxime Eeraerts
Wild bees, such as bumblebees and mason bees, have been considered important pollinators for sweet cherry. New research conducted in Belgium and Germany concludes that wild bees can do even more while having a positive effect on the pollination contribution of honeybees.
In this way, wild bees have a double positive effect, namely being excellent pollinators themselves and allowing honeybees to do their job better. This warrants a further call for wild bee conservation in agricultural landscapes, with benefits for fruit production.
EFFECTIVE CHAOS
In fruit crop orchards, such as sweet cherry orchards, compatible pollinizer cultivars are often planted in different rows to facilitate cross-pollination. To produce fruits, pollen from one cultivar must be transferred to the flowers of another — compatible — cultivar. Therefore, a flower-visiting insect that switches more often from one row to another has a greater chance to successfully cross-pollinate.
When foraging, honeybees take a very methodological approach, mainly visiting flowers on the same tree. In this way, they can efficiently collect pollen and nectar, but it reduces the probability that they will pollinate a flower. We know from wild bees, such as bumblebees, mining bees, and mason bees, that they forage in a slightly more chaotic way, changing trees and rows of trees more often than honeybees. This possibly explains why these wild bees are better pollinators than honeybees.
INCREASED HONEYBEE ACTIVITY
In sweet cherry orchards in Belgium, we examined whether the presence of bumblebees (mostly wild queens) affects the foraging behavior of honeybees. Interestingly, we found that the probability of a honeybee changing rows in an orchard increased markedly — we found an increase factor of 10! — as the number of bumblebees increases.
In addition, the number of flower visits per minute by honeybees increased when there were many bumblebees around. The influence of bumblebees on the honeybees’ foraging behavior could therefore potentially improve honeybees’ pollination efficiency by making their flower-visiting behavior slightly more chaotic.
A recent study in Germany found something similar. Here, researchers investigated the relationship between honeybees and fruit set in cherry orchards with different numbers of mason bees. They concluded that there was a positive relationship between honeybee numbers and cherry fruit set, but this positive relationship was only valid when there were many mason bees.
In orchards with low numbers of mason bees, no positive relationship was found between the number of honeybees and fruit set. Presumably, mason bees have the same effect as the bumblebees, namely that they influence honeybee behavior, making honeybees more efficient pollinators.
This synergistic effect of wild bees on the pollination contribution of honeybees was also already confirmed in a study of almonds, a crop that also depends on cross-pollination and is planted in a similar way to sweet cherry.
SUPPORTING THE CAUSE
Maintaining populations of wild bees around and in fruit orchards is useful, as they are efficient pollinators themselves and increase the pollination success of honeybees. Supporting or managing wild bees is also useful. Measures to boost wild bees include planting (mixed) hedgerows or allowing weeds or sown wildflowers to flower, for instance, in field margins. Managing wild bees can be done by providing nesting opportunities for mason bees. In this way, growers would become less dependent on a single managed bee species, the honeybee.