Project

Efficient pollination by insects, especially bees, is critical to ensuring food security and yields of many crops. Production of soft fruit such as strawberries in the UK was worth around £360m annually at the time of the project, and was growing year on year, but depends heavily upon pollination by insects, particularly bees.

When pollination is inadequate it frequently results in misshapen fruit. Owing to inadequate numbers of wild pollinators in agricultural ecosystems, strawberry growers rely heavily on commercially-bought colonies of bumblebees to try to improve pollination, but this is not always sufficient. Misshapen fruit must still be harvested despite poor sales potential in order to control pest insects that otherwise build up on them, so under-pollination causes a significant unwanted cost to growers.

Successful fruit production requires bees to carry pollen between flowers of the same crop species. Foraging bees often specialise on one species, which helps ensure this pollen transfer. Plants encourage this by providing distinctive cues such as unique flower odours, colours or shape which bees remember. Low doses of caffeine make bees remember cues such as floral odour more accurately, and increase bees' foraging activity.

This project investigated whether it was possible to prime managed bumblebees on strawberry farms to prefer foraging on the flowers of the crop, in order to pollinate them more effectively.

The project carried out experiments to test the ability of caffeine to improve crop pollination in field and laboratory settings. Bumblebees were provided experimentally with caffeinated nectar alongside a synthetic strawberry flower's scent. Since caffeine improves bees' memory for the scents of flowers, the project tested whether these bees showed increased foraging activity and attraction to strawberry flowers when they received this priming treatment.

The team predicted that if the preference of commercial bumblebees for strawberries was improved, the bees would visit more flowers, be more efficient at pollinating the crop and thus enable the production of higher-quality, more valuable fruit.

Field tests of this technology were performed on working farms using bumblebees to pollinate their strawberry crop, measuring fruit quality and yield resulting from this bumblebee-priming technology. The outdoor trials were supported by laboratory and semi-field experiments that optimised the system to find the best dose and timing of the priming treatment. A final economic assessment, in consultation with the project's collaborative private sector stakeholders who invested in this research, considered the potential financial benefits to the farmer of using caffeine-primed bees.

The project anticipated that evidence for enhanced pollination services delivered by bumblebees would provide a compelling commercial opportunity that adds value to bee colony provision, and could ultimately lead to enhanced pollination and fruit set in other pollinator-dependent crop species.