Effects of carbon dioxide on levels of biogenic amines in the brains of queenless worker and virgin queen honey bees (Apis mellifera)

Several experiments were conducted to examine the effects of exposure to CO2 or CO2 containing 20% O-2 on the amounts of biogenic amines in the brain, and on development of ovaries in worker and queen honey bees. When workers were fed pollen and exposed to CO2, their ovaries were less developed and brain dopamine (DA), tryptophan (TRP) and tyrosine (TYR) levels were significantly reduced versus untreated controls that were also fed pollen. If workers were not fed pollen and exposed to CO2, the differences in brain amine content between untreated controls and CO2-treated workers were not significant; however, a significant reduction in brain TRP and TYR levels through time was found for both groups of workers. Treatment with CO2 stimulated free-running queens to lay eggs sooner than untreated free-running queens, but CO2 narcosis had no significant affect on queen brain chemistry. However, the brain chemistry of caged queens (many queens caged within a single colony) responded differently from free-running queens. Treatment with CO2 caused a 45% reduction in dopamine levels in the brains of free-running queens, whereas dopamine levels of caged queens were not affected by treatment with CO2. This study shows that the brain dopamine levels of workers and queens do not change to the same degree in response to CO2 treatment. For workers, this study suggests a positive relationship between brain dopamine and the extent of ovarian development.