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

Abstract

Background. The age of an insect strongly influences many aspects of behavior and reproduction. This interaction 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 is 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 an individual honey bee would be important to provide a measurement of colony health. 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. Methods. We established single-cohort colonies to obtain age-matched nurse and forager bees. 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. Results. Our analysis showed that pteridine levels were higher in foragers than nurses of the same age, and pteridine levels significantly increased with age in a linear manner. Head weight significantly varied with age increasing until approximately 28 days of age, then declining thereafter for both nurse and forager bees. Discussion. Although the relationship between pteridine levels and age was significant, a large amount of variation in the data yielded an 8-day window in age estimation. This allows an unambiguous method to determine whether a bee may be a young nurse or old forager. Pteridine levels in bees do not correlate with age as well as in other insects. However, most studies used insects reared under tightly controlled laboratory conditions, while we used free-living bees. The dynamics of head weight change with age is likely to be due to growth and atrophy of the hypopharyngeal glands. Taken together, these methods represent a useful tool for assessing colony demography after a colony experiences a stress event. Future studies utilizing these methods will provide a more holistic view of colony health.