Resilience of pollinators in a changing world: impact of developmental environment on metabolism and energetic budgets in social and solitary bees

All animals need a balance of key nutrients, such as protein, carbohydrate and fat, in their diets for growth, maintenance and reproduction. Many animals can alter their food preferences to adjust their intake of nutrients. However, different environmental conditions, such as temperature, may necessitate different balances. Consequently, a healthy nutrient balance that animals prefer at one temperature may be unhealthy - and not preferred - at another. Thus, a hotter climate may change animals' needs and preferences within a landscape. For pollinators this is an unassessed and possibly serious threat both to their health and their pollination services upon which we depend for our food security.
Globally, one third of all crops rely on flower choices made by animal pollinators, especially bees. The pollen and nectar collected by bees from different crops vary widely in the content of carbohydrate, protein and fat content. Bees' health depends on access to a mix of nutrition appropriate for the conditions - but the climate is heating up, so this ideal mix may change. Crucially, if this affects bees' flower choices, then the pollination services bees provide today may not be the same at higher temperatures. We need to understand the implications of changing bee preferences on their health and on the services they provide. Once we understand bees' dietary needs, and how these needs might change in warmer climates, we can design appropriate, future-proof mitigation/intervention measures.
Our overarching aim is to measure and model the effects of changing nutrition and temperature in two wild bee species that are key pollinators in the UK. Bumblebees (Bombus terrestris) are important commercial pollinators of soft fruit, beans and tomatoes; red mason bees (Osmia bicornis) are highly effective pollinators of apples and other top fruit. Together they represent two contrasting life histories of UK wild bees. Bumblebees are social: they have workers that provision larvae throughout development, and that can control the temperature of their nest and therefore the developmental conditions of the brood. Red mason bees are solitary, provide larvae with a single pollen ball before hatching, and are unable to control developmental temperature beyond choosing a suitable nest site.
In both species we will gather detailed data on how the combination of nutrition (protein, carbohydrate and lipid) and temperature (realistic climate projections) affects growth, metabolic rate and survival, establishing the best diet for each of these variables at each temperature. Then we will test whether adults can maintain optimal diets for larvae when the temperature changes. This will provide insights into whether bee communities provisioning their young will be resilient to changing landscapes and climates. It will test for the first time whether provisioning adult bees respond dynamically to changing nutritional needs of young, and therefore how parents and larvae interact to ensure larvae receive a balanced diet. Finally we will use our data to create detailed energy budget models, which will test hypotheses about how bumblebees' and mason bees' differing lifestyles may underlie different physiological ways of dealing with climate heating, and will also predict changes in bees' flower preferences as climates heat up. The results will pave the way for (1) understanding and predicting which crops are vulnerable to pollination deficits on the basis of bees' changing nutritional preferences, and (2) designing bespoke, targeted management interventions such as pollinator-specific wildflower strips.

Animals must balance their macronutrient intake to support growth, maintenance and reproduction. To do so, many animals adjust their macronutrient intake by altering the food they ingest. Such nutritional preferences may depend upon environmental conditions. For example, some species' carbohydrate intake increases in warmer conditions. Bee species obtain nutrition primarily from flower nectar/pollen. In doing so, they provide pollination. Our preliminary data suggest bees' nutritional intake may change in hotter environments. If this is the case, then bees' floral preferences may change with broad consequences for many flowering plants and human food production.
We will rear larvae of social bumblebee workers and solitary red mason bees at three temperatures that are predicted from climate scenarios. We will feed them arrays of artificial diets containing different nutrient ratios (protein, carbohydrate and lipid), measuring larval body size, survival, consumption and excretion. In the adults that eclose, we will measure multiple traits (e.g. body size, metabolic rate) to establish how nutrient balance affects adult morphology/physiology.
We will then test whether adults foraging in flight cages can choose ratios of imbalanced artificial diets to maintain an optimal nutrient balance within provisions for larvae growing at different temperatures. Bumblebee workers switch to gathering more protein-biased nutrition when colonies contain offspring. However, whether adults dynamically adjust composition of nutrition they supply to match the needs of young is poorly studied. This work will give insight into how climate-altered requirements may affect visitation of key crops based on their nutritional content.
Finally, we will incorporate data into Dynamic Energy Budget models which will test and predict species-specific effects of developmental environments upon physiological processes, predict impacts upon ecosystem services, and improve existing mitigation measures.