Honeybee males use highly concentrated nectar as fuel for mating flights

• Honeybees carry nectar in the crop as fuel for flight but mass may be cost burden.
• Honeybee males use very concentrated nectar (>70%) as fuel for mating flights.
• The concentration of fuel for flight is significantly higher in males than workers.
• Males might use very concentrated nectar to increase their mating success.

Honeybees use nectar held in the crop as their main source of energy for flight but the mass of the crop nectar load may be a cost burden. This study investigated whether males of the honeybee Apis mellifera adjust their nectar fuel load and concentration to enhance the success of mating flights. When the crop content was compared between males staying in the hive and those departing, the latter group had the larger volume (median, 5.0 μl; range, 0.0–17.8 μl) and higher concentration (median, 71.6%; range, 49.0%–77.6%), indicating that departing males load concentrated nectar as fuel before mating flights. Moreover, the crop nectar concentration was significantly higher in departing males than in departing workers. These results suggest that concentrated nectar is advantageous to males because it provides more sugar for energy at lower mass and secures longer or more effective mating flights for higher chance of reproductive success. No significant effect of age was detected in crop volume, and concentration and amount of dissolved sugars in the crop content. In addition, laboratory experiments showed that males had only about 5 μl of nectar in the crop soon after feeding, irrespective of fed volume (5–15 μl), suggesting they do not hold much nectar in the crop but send it rapidly to the midgut, unlike workers.

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