A multi-year study published on 25 November found evidence that commodity crop production – such as soyabean farming – could be depleting honey bees’ access to food sources.

Bees are vital to the world’s food chain, pollinating one third of the world’s food crops including oilseeds, vegetables and fruit. Pesticides are believed to be a major contributor to the collapse of bee colonies, with the European Commission approving a ban on the world’s most widely used class of insecticide, neonicotinoids, in 2018.

In the study, published in the Proceedings of the National Academy of Sciences, scientists examined the health of honey bees in Iowa soya fields which showed how damaging the lack of variation in pollen could be. The expansion of farmland had driven a steep decline in native tall grass prairie, depleting both the quantity and variety of food sources available to honey bees, making them more susceptible to disease, the New Food Economy wrote.

Researchers from Iowa State University and the University of Illinois monitored the health of honey bees near soya farms with varying levels of productivity over the course of two years.

They placed 10 bee apiaries containing four colonies each next to soyabean farms at least one mile away from each other. The fields were highly cultivated (73% or more of their surrounding area was covered by crop land) or mildly cultivated (53% or less).

For each production level, the researchers then measured average bee populations, fat levels and weight of honey collected.

Typically, bees were supposed to produce honey for their colony from spring through autumn to have enough food to survive the winter. However, the researchers found that bees near soya farms were turning to food stores as early as August and by mid-October, had consumed all the gains food they had made in the spring and summer.

According to the study, the greatest weight gain happened when soyabean fields were in bloom. When the flowers fell off in late August, they may have taken the bees’ largest nectar source away with them, the New Food Economy reported.

Around the same time, both immature and adult bee populations dropped for both cultivation levels, as did average fat content.

There was also a notable difference between bee activities on high cultivation versus low cultivation fields: colonies near the more intensively planted farms gained honey at a significantly faster rate than colonies near the latter, suggesting that bees could momentarily benefit from industrial farming in one regard.

Researchers attributed this to being surrounded by more soya crops, as well as more field edges, which contained an abundance of clovers, a flowering plant that grew low to the ground. However, that initial burst of activity did not last.

In a separate experiment, the team placed ten honey bee colonies near a separate farm in Ames, Iowa. Halfway through the season, scientists moved half of the colonies to a reconstructed tallgrass prairie containing plants that bloomed in late summer and early fall not found on farms.

As a result, the bee colonies saw significant growth in weight and fat content, increasing their chances of survival in the winter, the New Food Economy reported.