New paper in Microbial Ecology!

We humans often change how we eat when we're sick, craving comfort food, sipping more tea, or losing our appetite. So, what about honeybees? When infected with a harmful parasite, do they eat more sugar to make up for lost energy? We investigated just that in our new study, which combines a broad review of existing research with a laboratory experiment.

The parasite in question is Nosema ceranae, a microscopic gut invader that infects honeybees. It’s widespread and harmful, damaging the digestive system and shortening bees’ lives. Given how important bees are for pollination and food production, understanding how they cope with this infection is crucial.

Since Nosema damages the gut and drains the bees' energy, we asked if infected bees eat more sugar to compensate. After all, sugar is their primary fuel for flying, foraging, and staying warm. To answer the question, we did two things:

1. Meta-Analysis: We gathered data from 15 previous studies, analyzing sugar consumption in healthy vs. infected bees. This allowed us to look for overall patterns across different experiments.

2. Experiment: We also conducted a new lab experiment. We infected bees under carefully controlled conditions and tracked how much sugar they consumed. We also checked the bees’ blood sugar levels.

Surprisingly, both the data review and the new experiment showed the same thing: there was no meaningful difference in sugar consumption between healthy bees and infected ones. Even the bees' sugar levels in their "blood" stayed about the same. This goes against the common idea of "compensatory feeding," where sick animals eat more to restore lost energy. But there are a few catches. First, older bees might be different. Most studies, including the new experiment, used relatively young worker bees. But older bees, especially foragers that fly outside the hive, have much higher energy needs. Some earlier studies suggest that older infected bees might eat more sugar, but there’s not enough data yet. Second, lab bees aren't wild bees. Bees burn more energy flying in the wild and may respond differently to illness than lab-kept bees. Studies on free-flying, infected bees have shown signs of energy stress, like changes in sugar levels and flight behavior.

A video showing typical stages of many honeybee experiments (in order of appearance): a frame with newly emerging bees, marking the bees, releasing them into the hive, recollecting them after a period of normal development, individually feeding them on Petri dishes, and housing them in laboratory cages. Video credit: M. Ostap-Chęć.

With bee populations under pressure from parasites, pesticides, and climate change, knowing how infections affect their behavior helps us better protect them. While Nosema ceranae is bad news for bees, it doesn’t seem to change how much sugar they eat, at least not in relatively young bees under lab conditions. But the story might be different for older, hardworking bees out in the wild. In any case, next time you see a bee buzzing from flower to flower, remember: it might be dealing with illness in ways we’re only just beginning to understand.

Check out the full paper here.