Changes in food source profitability affect Nasonov gland exposure in honeybee foragers Apis mellifera L.

Summary.

When arriving at a known artificial food source, foraging honeybees usually perform circular flights around the feeding place prior to landing. During these flights bees expose their Nasonov gland, an exocrine gland located at the base of the 7^th tergum, that releases a complex blend of volatiles. This behavior may continue even after the bee starts food ingestion. The proportion of bees exposing the Nasonov gland and the duration of its exposure before and during feeding for individual bees were quantified. Trained bees collected sugar solution during 12 visits from a feeder located at 160 m from the hive. Five different reward programs were presented: three constant and two variable. The constant programs offered 0.6, 1.2 or 2.4 M sugar for all 12 visits, while the variable programs delivered either 0.6, 1.2, 0.6 M or 0.6, 2.4, 0.6 M, four visits for each molarity. Results showed that sugar concentration changed the thresholds and durations of Nasonov gland exposure. However, this relationship was found only for Nasonov exposure before bees began to feed. During feeding, a protruded Nasonov gland was only observed for bees that had exposed it prior to feeding; suggesting that Nasonov gland exposure before feeding is a releaser of the during-feeding exposure. In variable reward programs, changes in sugar concentration were followed by changes in both thresholds and durations of exposure. However, Nasonov gland exposure during feeding did not appear to decrease based on measurements of the low profitability during the current foraging visit. These results suggest that Nasonov gland exposure is programmed on the basis of reward expectations, with the bees having acquired this information in the previous foraging visits to the food source.