Solitary bee larvae prioritize carbohydrate over protein in parentally provided pollen

Abstract

10 1. Bees, important pollinators, have declined significantly in recent decades, and human-11 induced changes to nutritional landscapes are partly responsible. Changes to nutritional 12 quality rather than quantity have been overlooked as a threat to bee health. Yet 13 knowledge of bee nutrition is currently largely restricted to adults of social species. 14 Larval stages, where most growth occurs, are relatively understudied -perhaps because 15 most social bees provision progressively and collectively, making nutrition difficult to 16 trace. 17 2. In mass-provisioning solitary bees (Osmia bicornis L.), we can manipulate and follow 18 larval nutrition, and thereby determine effects of changes in diet quality. Under the 19 Geometric Framework for Nutrition, we restricted larvae to 6 diets: 3 20 protein:carbohydrate ratios and 2 nutrient concentrations. We asked: (a) which diets 21 maximise body size and survival, (b) what consumption rules do larvae follow when 22 nutrients are imbalanced? Finally, (c) given a choice of complementary diets, are larvae 23 able to select a dietary balance? 24 3. Larvae pupated after consuming a fixed carbohydrate amount, but tolerated a wide range 25 of protein. Body size and survival were maximised on our lowest P:C ratio diet, and 26 having consumed the most carbohydrate. When eating freely from two diets, larvae 27 converged on a P:C ratio of 1:1.8, but not an overall nutrient intake target. Nevertheless, 28 larvae maintained stable carbohydrate intake, while protein intake varied with the 29 available diet.304. Our results suggest solitary bee larvae regulate carbohydrate most closely, but that 31 excessive indigestible material may limit their actual nutrient intake. Carbohydrate may 32 be critical to overwinter survival, and/or may be more limiting than protein. The large 33 variation in protein tolerated, despite its importance, suggests bee larvae may be 34 vulnerable to landscape changes -and therefore reliant on parents to regulate protein. 35 Given the mixed evidence on whether parents can sense pollen protein content, our 36 results highlight bees' potential vulnerability to a "nutritional trap", i.e. where rapid 37 changes in their nutritional environment outstrip their evolved capacity to detect those 38 changes, impairing their fitness. 39 40

Differential effects of farming practice on cuckoo bumblebee communities in relation to their hosts

“…Not all plants produce pollen of sufficient nutritional quality to meet the requirements of bees (Filipiak, 2017a,b). Since bee larvae require specific nutrients for growth and development (Austin & Gilbert 2018), large quantities of food can not compensate for poor quality (Filipiak, 2018).…”

Impact of Biotic and Abiotic Stressors on Managed and Feral Bees

“…This finding highlights the importance of crop species and flower timing in providing B. terrestris with adequate food resources in intensively managed agricultural systems. At a specific nutrient level, it was found that carbohydrate regulation was the most important variable in maximizing O. bicornis body size and survival, where the larval pupation occurred only after ingesting a fixed quantity of carbohydrates, but variable amounts of protein [118]. The authors of this study propose that the wide range in larval protein consumption is a result of their dependence on maternal nest provisioning for obtaining protein, and hence explains O. bicornis vulnerability to changes in landscape floral composition.…”

“…Solitary bees also have similar nutritional requirements, for which most studies suggest that a departure from monoculture plantings is the best remedy [118,145,146,147]. For example, a range of seven to 1100 flowers or 0.9 to 4.5 flower heads is required to rear a single larva of 41 European bee species, depending on both species and host plant [148].…”

Larval nutrition impacts survival to adulthood, body size, and the allometric scaling of metabolic rate in adult honeybees

“…Bees meet all their nutritional demands via pollen and nectar collected from flowers (their main source of protein and carbohydrate respectively), and unlike the nymphs and larvae of traditional models of insect nutrient regulation, such as locusts and caterpillars, bee larvae are entirely dependent on the provisioning choices of adult bees. This means bee larvae likely have very little opportunity to selectively regulate their intake of nutrients (but see Austin and Gilbert, 2018). Honeybees are unique among bees in that in-hive nurse bees process the pollen and nectar brought back to the nest by foragers, and convert it to a nutritional substance known as royal jelly which they then regurgitate for larvae (Wright, Nicolson and Shafir, 2018).…”