Bumblebees adjust protein and lipid collection rules to the presence of brood

Abstract

Animals have evolved foraging strategies to acquire blends of nutrients that maximize fitness traits. In social insects, nutrient regulation is complicated by the fact that few individuals, the foragers, must address the divergent nutritional needs of all colony members simultaneously, including other workers, the reproductives, and the brood. Here we used 3D nutritional geometry design to examine how bumblebee workers regulate their collection of 3 major macronutrients in the presence and absence of brood. We provided small colonies artificial nectars (liquid diets) and pollens (solid diets) varying in their compositions of proteins, lipids, and carbohydrates during 2 weeks. Colonies given a choice between nutritionally complementary diets self-selected foods to reach a target ratio of 71% proteins, 6% carbohydrates, and 23% lipids, irrespective of the presence of brood. When confined to a single nutritionally imbalanced solid diet, colonies without brood regulated lipid collection and over-collected protein relative to this target ratio, whereas colonies with brood regulated both lipid and protein collection. This brood effect on the regulation of nutrient collection by workers suggests that protein levels are critical for larval development. Our results highlight the importance of considering bee nutrition as a multidimensional phenomenon to better assess the effects of environmental impoverishment and malnutrition on population declines.

Pollen Protein: Lipid Macronutrient Ratios May Guide Broad Patterns of Bee Species Floral Preferences

“…Recent studies have demonstrated further associations between bee foraging preferences and health and pollen P:L ratios. For example, entire bumble bee colonies regulate protein and lipids to similar ratios as we predicted previously [10]. We found that the P:L of different pollens used in agricultural cover-cropping systems have differential effects on B. impatiens colony ovary activation and wax production [20]; we also found that P:L ratios and the protein content of an invasive plant species may be more attractive to the bee community (including solitary bees) than surrounding native plants, presenting a possible mechanism of invasive competitive ecology [19].…”

“…As data for A. mellifera and O. cornifrons were not collected for systematic analysis, we acknowledge that these trends, while intriguing, require further study with a robust design. It is also likely that bee species' preferences and nutritional targets may be species, caste, and life-stage specific and not driven simply by higher or increasing nutrient concentrations or ratios [6,10,56]. Furthermore, bee foraging for particular pollen nutritional values may be attenuated by the limits of landscape availability.…”

“…For example, we can study host-plant shifts of bees as their ranges cover areas of plant species turnover, discuss evolutionary shifts of pollinators to new host plants based on diet composition [85], and changes of floral mating systems to other insect or vertebrate pollinators. We can test how variations in the P:L values of pollen species affect bee physiology and health in the lab and field [20]; more sophisticated geometric framework studies [10] are clearly needed for different bee species. Pollen nutrition may also be important for understanding invasive ecology and responses to climate change [19,50,86,87].…”

“…To this end, nutritional ecology theory, which focuses on the mechanisms of foraging for multiple nutrients [6,7], can offer a new perspective on plant-pollinator interactions that are useful for conservation. Bees integrate and balance multiple macronutrient resources when making foraging decisions that have consequences on their health and fitness [8][9][10]. Understanding the complex connections between the nutritional resources that plants provide and the nutritional needs of bees reveals insights into bee-flower symbioses and coevolution, and ultimately the assembly and stability of plant-pollinator communities.…”

Spatio-temporal dynamics of landscape use by the bumblebee Bombus pauloensis (Hymenoptera: Apidae) and its relationship with pollen provisioning

“…Consequently, the bees' movements shifted to include the land use categories with greater pollen heterogeneity [75,76] despite continued, albeit reduced, availability of blueberry flowers. Results from Kraus et al (2019) [77], who studied Bombus diets in captivity, also suggest that protein levels are critical for larval development, and these protein levels may be sustained from the more diverse plants.…”