Pteridine levels and head weights are correlated with age and colony task in the honey bee, Apis mellifera

Authors: Rinkevich, Frank; MARGOTTA, JOSEPH - Louisiana State University Agcenter; PITTMAN, JEAN - Louisiana State University Agcenter; OTTEA, JAMES - Louisiana State University Agcenter; HEALY, KRISTEN - Louisiana State University Agcenter

Submitted to: PeerJ
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/31/2016
Publication Date: 6/30/2016
Citation: Rinkevich Jr, F.D., Margotta, J.W., Pittman, J.M., Ottea, J.A., Healy, K.B. 2016. Pteridine levels and head weights are correlated with age and colony task in the honey bee, Apis mellifera. PeerJ. 4:e2155. https://doi.org/10.7717/peerj.2155.
DOI: https://doi.org/10.7717/peerj.2155

Interpretive Summary: The tasks performed by adult honey bees is mostly determined by age. Typically, young bees perform tasks within the colony such as feeding developing larvae, cleaning cells, and storing food, while older bees defend the entrance and forage for food outside of the colony. Disturbances to the colony age structure or changes in resource needs and availability can cause old bees to return to tasks inside the colony and induce young bees to forage outside of the colony. These colonies with altered demographics may perform poorly and are susceptible to colony losses. Therefore, being able to determine age structure within a colony may provide a useful measurement of colony health. Pteridines are pigments contained in the heads of insects and these pteridines accumulate with age, thus providing a method to evaluate honey bee age. However, no studies have investigated the utility of using pteridines to determine the age of honey bees. We collected bees of known ages from colonies with normal demographics as well as from single cohort colonies where all the adult bees were the same age despite being nurses or foragers. We measured the concentration of pteridines using fluorometric methods. We found that pteridines accumulate in a linear manner with age in bees from colonies with normal demography and with altered age structure. However, the young foragers from single cohort colonies had lower pteridine concentration than normal aged foragers from colonies with normal demographics. Additionally, head weight in foragers from single cohort colonies was correlated with age, while there was no such correlation in bees from colonies with normal demographics. Therefore, the use of pteridines along with head weight can be used to determine age structure and, vis a vis, colony health.

Technical Abstract: The age of an insect strongly influences many aspects of behavior and reproduction. The interaction of age and behavior is epitomized in the temporal polyethism of honey bees in which young adult bees perform nurse and maintenance duties within the colony, while older bees forage for nectar and pollen. Task transition is dynamic and driven by colony needs. However, an abundance of precocious foragers or overage nurses may have detrimental effects on the colony. Additionally, honey bee age affects insecticide sensitivity. Therefore, determining the age of a set of individual honey bees would be important to assess if colony demography is altered. Pteridines are purine-based pigment molecules found in many insect body parts. Pteridine levels correlate well with age, and wild caught insects may be accurately aged by measuring pteridine levels. The relationship between pteridines and age varies with a number of internal and external factors among many species. Thus far, no studies have investigated the relationship of pteridines with age in honey bees. We established single-cohort colonies to obtain age-matched nurse and forager bees. Bees of known ages were also sampled from colonies with normal demographics. Nurses and foragers were collected every 3-5 days for up to 42 days. Heads were removed and weighed before pteridines were purified and analyzed using previously established fluorometric methods. Our analysis showed that pteridine concentration significantly increased with age in a linear manner in both single cohort colonies and colonies with normal demography. Pteridine concentrations were higher in foragers than nurses of the same age in bees from single cohort colonies. Head weight significantly increased with age until approximately 28-days of age and then declined for both nurse and forager bees in single cohort colonies. A similar pattern of head weight in bees from colonies with normal demography was observed but head weight was highest in 8-day old nurse bees and there was no relationship of head weight with age of foragers.