Bumblebees show mouthpart responses to sweet and bitter solutions

Bumblebees extended their mouthparts after tasting sweet solutions and shook their heads or wiped their mouths after tasting salt or quinine, according to a study published in the Proceedings of the National Academy of Sciences. Researchers from Macquarie University and Southern Medical University presented bees from 18 colonies with droplets of 60 percent sugar, 20 percent sugar, plain water, 5 percent salt, or 1 millimolar quinine.

They recorded the insects' reactions under varied conditions including heat stress, satiety, and drug administration.

Responses varied with context Bees kept extending their mouthparts after consuming the sweet solutions, a behavior the researchers called post-consumption glossa. The same bees showed clear rejection movements when given salt or quinine. When colonies were heat-stressed, reactions to water and salt solutions shifted from neutral or negative to positive.

Researchers compared the change to a human preference for electrolyte drinks after heavy exertion.

Implications for insect sentience research A Macquarie University researcher said the mouthpart movements indicate subjective evaluation rather than simple chemical reflexes. The study tested multiple colonies and conditions to rule out reflexive responses.

An entomologist not involved in the work noted that most prior insect research has focused on negative states such as pain or fear. The current findings add data on positive states, the entomologist said.