The next time you see a bee hovering around a fruit tree, you're probably witnessing pollination in action. Pollination is what allows a plant to produce seeds and fruit, and as research has shown, insect pollination can greatly improve the quality and quantity of fruit produced.

There is increasing evidence of a decline in pollinator populations around the world. The consequences for agriculture could be significant. In 2008, some scientists calculated the economic value that insect pollination brought to global agricultural production. The figure they obtained was €153 billion a year; it is likely to be much older now.

Some fruit crops require very specific types of insect pollination. Take blueberries. Their flowers have specialized anthers (the pollen-bearing part of the stamen) that release large amounts of pollen only when visited by certain pollinators, such as blueberry bees, bumblebees, and mining bees. In a process called buzz pollination, bumblebees vibrate their bodies at a certain frequency when they visit blueberry flowers. This triggers vibrations in the anthers that cause the pollen to explode. The special shape of blueberry flowers and the number of flowers on a blueberry bush means there is no way to mechanically pollinate blueberry plants on a commercial scale.

In recent years, blueberries have become increasingly popular due to their perceived health benefits. They are now planted all over the world, including areas where their natural pollinators are not found, such as South Africa, where blueberry exports to the world have increased from 1792 tons in 2014 to 20 tons in 013.

In South Africa there are no native pollinators for the fruit in the country, and local honey bees are not considered an efficient substitute. Farmers are considering importing large bees, such as bumblebees, that are not native to the country. (The large bees that South Africans may see in their gardens that look like bumblebees are actually carpenter bees.) But that could devastate local environments: bumblebees are strong competitors and often outcompete native pollinators for resources, as has been seen in Argentina.

Until now, little research has focused on how honey bees actually act as pollinators of blueberries in South Africa. It was important to fill this knowledge gap, as the honey bee is the only pollinator in the country that is found in large enough populations, is easily managed, and can be moved to meet commercial needs.

In two related studies, we tested the pollination ability of honey bees on some of the most common blueberry varieties planted in South Africa. Honey bees were found to be reliable pollinators of blueberries, increasing fruit number, fruit diameter and mass, and decreasing fruit development time. Importing larger bees like bumblebees is simply not necessary.

But our findings also suggest that honey bees do better on certain blueberry varieties. This shows that it is important to test the efficacy of honey bees on new blueberry varieties brought to countries where honey bees are the only commercially available pollinators. This information can guide variety choice and ultimately improve crop yields and profitability.

Honey bees in action

Many people in the commercial fruit industry think that honey bees are poor pollinators of blueberries. There are some reasons for this.

First, honey bees are substantially smaller than natural blueberry pollinators and cannot vibrate their bodies at the frequency necessary for efficient pollen release.

Also, honey bees are often reluctant to forage in cold weather. Therefore, there may be little pollination during periodic cold spells. They have slower feeding times and deposit less pollen on each visit to a plant than other pollinators such as bumblebees.

These concerns are valid, but we show that honey bees are much better pollinators of blueberries than farmers may think. Our research shows that as new cultivated blueberry varieties become available, buzz pollination may not be as important as it was with earlier varieties.

Improvements and doubts

We compared fruit produced through hand pollination with fruit produced through bee pollination.

Honey bee pollination consistently produced better results than no pollination. We found that, on average, when blueberry plants were not pollinated, they produced 47% fewer fruits and the fruits were 13% smaller than with bee pollination. Blueberries also took 6% longer to ripen without honey bee pollination than with it.

There is room for improvement. Bees were able to fully pollinate some varieties of plants, but they were not as efficient at pollinating other varieties.

Certain varieties are not reaching their full fruiting potential because not enough high-quality pollen is being transferred between flowers. Our research suggests that this may not be due to bee inefficiency. Instead, it all comes down to pollen movement between varieties. We also suggest that the way blueberries are planted makes a difference and we will explore this hypothesis in a future article.

Next steps

We hope that our findings discredit the notion that highly invasive pollinators need to be imported into South Africa.

We are not the only ones testing the efficiency of honey bees as pollinators. The importation of bumblebees is prohibited in India due to the risks they pose to local ecosystems. The researchers are testing the pollination performance of honey bees in different environments, including greenhouses.

This type of research can help guide policymakers and farmers in deciding how best to increase blueberry yields without putting native pollinators and flora at risk.