Hi all
I think it's pretty clear that honey bee foragers do not have access to the nutritional value of pollen and rely on other cues to decide which pollens to collect. For one thing, they don't eat pollen in the field, they just collect it. It's likely the answer lies in the pollenkitt:

> POLLEN GRAINS of entomophilous plants are typically coated with an oily, sticky, and frequently yellow-colored material, commonly referred to as "Pollenkitt". Several functions have been attributed to pollenkitt, some relating to the successful dispersal of pollen by animals and others to the biology and survival of the male gametophyte prior to, during, and following pollination. This paper addresses the chemistry of pollenkitt from the perspective of its possible role in providing chemical - particularly olfactory - cues to pollen-seeking flower visitors.

> Occurrence of specific volatile cues may underlie the pollen-specificity exhibited by many solitary bee species, as well as the similarity in plant taxa visited for pollen by honey bees throughout western Europe and the United States ... Results from this study indicate that the chemical composition of pollenkitt varies interspecifically and that it is the likely carrier of pollen aromas. Constituents of pollenkitt could thus potentially be used as recognition cues by pollen-seeking flower visitors.

Dobson, H. E. (1988). Survey of pollen and pollenkitt lipids–chemical cues to flower visitors?. American journal of botany, 75(2), 170-182.

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> Knoll (1930) was the first to address the origin of pollen scents and insightfully proposed that pollen odor arises from the pollenkitt. Knoll coined this term for substances that cause pollen grains to clump, more specifically in reference to the oily and often sticky, colored coating on the outside of pollen grains. Up to then, pollenkitt had attracted only spotty attention.

> The chemical confirmation that pollen emits odors has given new impetus to studies of the role of pollen odor in pollination ecology, especially in attracting flower-visiting insects and modulating their foraging behavior, and in defending pollen against pollen-feeding organisms and pathogens (Dobson 1994, Dobson et al. 1999).

Dobson, H. E., & Bergström, G. (2000). The ecology and evolution of pollen odors. Plant Systematics and Evolution, 222(1-4), 63-87.

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> Some flowers are deceitful in attracting animals, whereby they mimic oviposition sites, mates, or food sources of pollinator animals ... In each plant species, flower visitation is restricted to only a subset of the local flower-visiting animals by the phenology of bloom (e.g., seasonal, day versus night); the type, quality, and quantity of food rewards; the floral morphology, which limits access to the rewards; and the floral advertisement stimuli, such as colors, shapes, and scents, which variously stimulate animals to seek, locate, and land on the flowers. Most flowers are visited by a diversity of animal species, but only a few may actually effect pollination

Dobson, H. E. (2006). Relationship between floral fragrance composition and type of pollinator. In Biology of floral scent (pp. 150-202). CRC press.

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