INNOVATION FOR IMPROVED STRAWBERRY POLLINATION BY COMMERCIAL BUMBLEBEES USING CAFFEINE

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 is worth around £360m annually, is 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 will investigate whether it is 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 will carry out experiments to test the ability of caffeine to improve crop pollination in field and laboratory settings. Bumblebees will be provided experimentally with caffeinated nectar alongside a synthetic strawberry flower's scent. Since caffeine improves bees' memory for the scents of flowers, the project will test whether these bees show increased foraging activity and attraction to strawberry flowers when they receive this priming treatment. We predict that if the preference of commercial bumblebees for strawberries is improved, the bees will visit more flowers, be more efficient at pollinating the crop and thus will enable the production of higher-quality, more valuable fruit.

Field tests of this technology will be 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 will also be supported by laboratory and semi-field experiments that optimise this system to get the best dose and timing of the priming system. A final economic assessment in consultation with the projects collaborative private sector stakeholders who have invested in this research will consider the potential financial benefits to the farmer of using caffeine-primed bees.

We anticipate that evidence for enhanced pollination services delivered by bumblebees will 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.

Declining wild pollinator populations and increasing demand for soft fruit, year-round, means farmers increasingly rely on commercial or managed pollination services. Bumblebees in particular are excellent soft fruit pollinators, but there is scope to improve their efficiency and effectiveness, resulting in increased yield and fruit quality. There are also concerns about the impact of commercial bumblebees on wild bees, via competition for wildflower forage or vectoring of pathogens to the wild bees. Strengthening memory associations in Bombus terrestris for floral odours in strawberry crops would increase specificity and fidelity of bumblebees for the crop; this is expected to improve fruit yield and quality, as well as reducing interactions between wild and managed bees.

Headspace analysis will identify the composition of strawberry floral odour. We will create a synthetic odour blend to use in training. Consumption of caffeine strengthens bees' memory associations for odour in the lab; exposure to odours in the nest increases bees' preferences for the same odours outside the nest. Thus, we will test the potential of caffeine to improve bumblebee crop-specificity. We will use conditioning paradigms to train bees to associate crop-specific odours with a reward via provision of sugar solution containing floral odours in the nest, with and without caffeine added to the training solution. This will permit comparison of the preference for strawberry flowers and overall foraging activity and efficacy in the laboratory and the field. Detailed recording will be made of foraging preferences, activity levels before and after caffeine application and persistence of behaviours. On working farms, bee visits to strawberry flowers in polytunnels will be monitored, data on fruit set collated and floral constancy and pollen collection efficiency evaluated by analysis of pollen. An economic evaluation will establish the possible income benefits to farmers of this system.

Demonstrating the possibility of improving crop pollination by modifying pollinator experiences in the nest, via compounds in their food, has implications for agriculture and horticulture in the UK and internationally. Specifically our work will impact:

1. Growers and grower bodies. Farmers producing glasshouse and polytunnel crops using managed pollinators to deliver pollination services to crops will benefit by improved efficiency of commercial bee colonies, resulting in a larger percentage of Class I fruit, fewer misshapen fruit, less wastage and reduced disposal costs of unsaleable product. It is anticipated that this will represent a significant commercial advantage to UK growers. The innovation may also help to ameliorate problems experienced when pollinator effort decreases in high temperature and humidity conditions in polytunnels, by increasing pollinator foraging focus and activity using caffeine. The industry-led nature of this project, responding to the needs of a grower organisation (Berry Gardens), and direct collaboration with growers themselves will permit us to work in a participatory way with growers to maximise communication with results and facilitate eventual takeup of positive findings.

2. Global horticulture. The outcomes could provide a system of pollinator enhancement relevant to a wide variety of horticultural crops globally including citrus and almonds - both multi-billion dollar industries in the US that rely on managed pollinators. The outcomes will have wider implications since plant chemicals in nectar are found across many genera of plants, and understanding their effects on bees more widely will allow risk assessments of large monocultures on bee health and better understanding of factors that contribute to bee decline (Vanbergen et al. 2013).

3. Commercial bumblebee producers. This innovation aligns with existing strategies to make commercial bumblebees more effective for growers, e.g. Biobest's Turbo hives, and may permit refinement of other emergent technologies such as bee-vectored entomopathogen biocontrols. This provides an opportunity for bumblebee producers to take bumblebee production to the next level of technology. It also enables mitigation of some environmental impacts of commercial bumblebee production by reducing interaction between wild and managed bumblebees and thus potential disease transmission and competition for wild resources.

4. Beekeepers. The project will provide information about the impacts of plant compounds on bees and pollinators generally. Understanding measures that could increase bee foraging effectiveness may be of interest to bee enthusiasts more widely.

5. Schools and local interest groups. Our work will help grow the public's broader understanding of the diversity of life, the importance of pollinators and agricultural ecosystems and will be of particular benefit to conflicting agendas such as agricultural production and conservation biology which often have opposing goals. Pitting food production against conservation of biological diversity are both concerned with managing natural resources based on societal mandates: agriculture focuses on the production of foods, whereas the focus of conservation is on the maintenance of biodiversity. The rational response is to consider both challenges together, as explained by Cook & Varsheny (2010).

6. Policymakers. Demonstration of ways to improve performance of commercial bumblebees to enhance soft fruit product yield and quality will impact agricultural policy in UK and internationally and the scope to improve yield and quality through enhancing pollination rather than yet more chemical inputs will broaden the agro-ecological intensification debate.