Convergence of carbohydrate-biased intake targets in caged worker honeybees fed different protein sources

Abstract

SUMMARY The nutritional needs of bees are supplied by nectar carbohydrates and by protein and other nutrients in pollen but little is known of how bees achieve nutritional balance. Using newly emerged caged worker honeybees (Apis mellifera scutellata), we investigated whether bees maintain their intake target when confined to pairs of imbalanced complementary diets varying in protein to carbohydrate (P:C) ratio. Diets were formulated using three protein sources [casein, royal jelly or Feed-Bee® (a natural pollen substitute)] and sucrose. Within each protein type, honeybees switched between complementary diets and converged on the same P:C intake target. However, this target differed between protein types: P:C ratios were 1:12, 1:14 and 1:11 on casein, royal jelly and Feed-Bee® diets, respectively. Except for an early peak in protein consumption on royal jelly diets, these strongly convergent ratios remained constant over the 14 day experiment. This is probably due to the absence of brood, reflected in relatively stable values measured for haemolymph protein concentration and hypopharyngeal gland activation in bees on Feed-Bee® diets. Performance of caged workers was also assessed in terms of survival and ovarian activation. Survival was highest on casein diets and lowest on Feed-Bee® diets but ovarian activation was highest on royal jelly diets and lowest on casein diets. This may be due to additional components in Feed-Bee® and royal jelly (e.g. fatty acids), which are needed to activate the ovaries but also reduce survival. Nutrient intake of broodless workers is directly related to their own physiological requirements, and the strong carbohydrate bias may reflect the high metabolic rate of honeybees even under resting conditions.

Pathogen-associated self-medication behavior in the honeybee Apis mellifera

“…Protein levels for instance can decrease in bees from colonies with low pollen stores which in turn can lead to reduced individual immunocompetence (Alaux et al 2010). Moreover, the protein-carbohydrate ratio is important for the nutritional intake and physiological demands of stressed or sick bees (Altaye et al 2010). We here show that the in-hive worker bees might be in an exceptionally important position to distribute selectively honey in the colony that affect their own health but potentially also that of other nestmates.…”

Macronutrient ratios in pollen shape bumble bee ( Bombus impatiens ) foraging strategies and floral preferences

“…3 and 4), although lipids appeared to have had a phagostimulatory effect at lower concentrations. Thus, B. impatiens, and likely other bumble bee and generalist bee species, appears to have a sophisticated ability to assess pollen nutritional quality and forage selectively to reach nutritional intake targets (6,(41)(42)(43).…”

Antioxidant supplementation can reduce the survival costs of excess amino acid intake in honeybees

“…hypopharyngeal gland development - Crailsheim et al, 1992). Furthermore, this intake target contains more carbohydrate than that preferred by bees fed diets containing protein in the form of casein (between 1:6.5 P:C -1:12 P:C) (Altaye et al, 2010;Archer et al, 2014a). This is presumably because free amino acids provide a more readily accessible form of nitrogen that is absorbed more quickly and efficiently than proteins (Rønnestad et al, 2000).…”

“…The P:C ratio is the ratio of amino acids to carbohydrate converted to the equivalent weight : weight ratio of proteins to carbohydrate used in past experiments on honeybee nutrition (e.g. Altaye et al, 2010). The total AA concentration is that of all ten essential amino acids, each of which has the concentration given in the Individual AA (M) column.…”

“…A poor diet, due to land use changes reducing the availability and diversity of floral resources, may help drive these declines (Vanbergen and the Insect Pollinators Initiative, 2013). In keeping with this idea, nutrition is a key determinant of honeybee survival (Altaye et al, 2010;Archer et al, 2014a): African honeybees (Apis mellifera scutellata) fed high protein diets experience reduced survival and European honeybees (Apis mellifera) survive poorly when fed diets rich in essential amino acids (EAAs) (Paoli et al, 2014). To protect declining and threatened honeybee populations (Pirk et al, 2014) it is important that we better understand the association between diet and honeybee survival, and find ways of mitigating the costs of poor nutrition, especially in populations which are underrepresented in the literature (Archer et al, 2014b).…”