There’s nothing quite like a big, tasty strawberry. Previous research has shown that when bees visit the flowers of strawberries, the strawberries grow bigger. But this growth is hampered if the bees have been exposed to neonicotinoid pesticides.

“We studied bees that ingested clothianidin, a pesticide that was previously used in rapeseed to control flea beetles. Our study indicates that the substance made the bees slower and impaired their ability to pollinate the strawberry flowers,” says Lina Herbertsson, biology researcher at Lund University.

To test this idea, Herbertsson and colleagues had 12 cages with solitary bees. The bees were allowed to forage in rapeseed and strawberry flowers — but in half the cases, the rapeseed flowers had been treated with clothianidin, a common pesticide.

This pesticide has previously been shown to affect bees and make them slower, and this was also confirmed in the new study. But the researchers also found that when the bees first visited pesticide-treated rapeseed flowers and then strawberry flowers, the strawberries turned out smaller.

“Previous studies have shown that clothianidin affects wild bees negatively in terms of foraging speed, development and reproduction. Our results indicate that it can also impair the bees’ ability to pollinate strawberry flowers,” says Lina Herbertsson.

The study stops short of providing a reason for this. Basically, the team only established a correlation but did not zoom in on the exact mechanism that causes the strawberries’ stunted growth.

“In our study, we did not identify the cause for the lower strawberry weight, and after only having performed a single study under rather special circumstances, we also don’t know if this is a general pattern,” Lina Herbertsson says.

However, this is yet another reason to be careful with pesticides. Honeybee numbers are dwindling across the world, and much of that is owed to the use of pesticides — specifically neonicotinoids. This class of pesticides affects the bees’ nervous system and leaves them vulnerable to a number of other problems such as disease. In the European Union, clothianidin is now banned as of 2018, but it’s still used in other places — but even in the EU, other pesticides could have a similar effect.

“Although clothianidin is now banned, other substances that affect the nervous system of insects in a similar way have partly replaced it. It is therefore of the utmost importance to continue this research and investigate how these substances affect bee behavior and pollination,” Lina Herbertsson concludes.

Journal Reference: Lina Herbertsson et al, Seed-coating of rapeseed (Brassica napus) with the neonicotinoid clothianidin affects behaviour of red mason bees (Osmia bicornis) and pollination of strawberry flowers (Fragaria × ananassa), PLOS ONE (2022). DOI: 10.1371/journal.pone.0273851