Not the nurses: old honey bee workers of resource-handling age primarily interact with and consume pollen substitute...

Pollen is essential for western honey bee (Apis mellifera L.) brood development, but the quality and quantity of pollen in the environment varies seasonally. Beekeepers often provide pollen substitute patties (PSPs) as a source of protein, lipids, and micronutrients when high-quality natural pollen is unavailable. Previous dye-tracing research has established that honey bees do not use PSPs the same way they use natural pollen; it is consumed by adult workers but is not stored or fed to larvae. Here, we determined the age at which adult workers interact with and consume PSPs to understand PSP utilization in honey bee colonies. We released cohorts of marked, newly emerged workers into hives containing dyed PSPs, undyed PSPs (negative control), dyed fondant (positive control), and dyed modeling clay (consumption control). We recorded the number of marked workers interacting with the treatments for 4 weeks following worker release. Additionally, we collected 20 marked workers daily from all colonies to assess the presence of dye in their guts. We constructed generalized linear mixed effect models and used Akaike's Information Criterion to perform model selection. Using our top models, we found PSP interaction and consumption gradually increased with worker age until peaking between 18 and 22 days post cell emergence. These patterns suggest that older workers of pollen packer and foraging age, rather than nurse bees, are the primary consumers of PSPs. Our research suggests that PSP utilization may be driven by resource handling behaviors or carbohydrate consumption, rather than brood provisioning, when colonies are not pollen-limited.