Parasitized honey bees are less likely to forage and carry less pollen

Background/Question/Methods

Research into loss of pollination capacity has primarily focused on documenting pollinator declines and their causes with comparatively little attention paid to how stressors may affect pollinating behaviour of surviving pollinators. Apis mellifera is one of the world’s most important generalist pollinators, and Nosema apis is a globally widespread microsporidian gut parasite of adult A. mellifera. It is considered less virulent than the also widespread N. ceranae.  Both gut parasites change the metabolism of their hosts and therefore may affect foraging choices and foraging behavior. We individually fed 960 newly emerged A. mellifera either a sucrose solution or a low dose of N. apis spores in a sucrose solution and tagged them with a unique radio frequency identification (RFID) tag.  We also measured pollen available for pollinating on returning foragers, observed foraging choices in an artificial floral arena, and conducted a capture-release experiment to test hive orientation behavior.

Results/Conclusions

Spore-fed bees were less likely to forage, started foraging when they were older, and stopped foraging when they were younger than non-inoculated bees. However, most inoculated bees took more foraging trips in their lifetime than non-inoculated bees. Inoculated and non-inoculated bees did not differ in the number of foraging trips taken per day, the total hours foraged, or homing ability. Inoculated returning foragers were 4.3 times less likely to be carrying available pollen than non-inoculated returning foragers and the number of pollen grains carried was negatively correlated with the number of N. apis spores. In the artificial flower arena, inoculated bees had a tendency (p=0.061) to choose sugar flowers over pollen flowers, compared to non-inoculated bees which visited pollen and sugar flowers equally. These results demonstrate that even low doses of a widespread disease of A. mellifera may adversely affect bees’ ability to pollinate.