A blog post highlighting the article written by Cook, Durzi, Scheckel and Breed in Insectes Sociaux

Written by Chelsea Cook

My best friend Kika is about to have her first child. She is eating nothing but organic food, staying away from alcohol & caffeine, and lightly exercising. One thing she doesn’t have to worry about is the temperature at which her baby is developing. Humans are endotherms – we regulate our own body temperature right around 98.6°F, and with even just a degree off we feel terrible.

Honeybees are individually ectothermic, which means they use their environment to regulate their body temperature. As a hive, however, honey bees work together to maintain a narrow range of temperatures, between 96°-97°F. One of the main reasons why the bees do this is to maintain the optimal temperature range for the developing larvae. If the temperature inside the hive gets hotter than 97°F, the developing larvae inside become malformed (Himmer 1932) or will have altered behavior as adults (Groh et al. 2004).

Honey bees actively work to keep their hive cool. Honey bees will collect water to spread over the developing larvae for evaporative cooling (Kühnholz & Seeley 1997), spread themselves out inside and outside of the hive to allow for airflow (Bonoan et al. 2014), and will fan their wings to circulate cool air. All of these jobs are performed by groups of bees, who actively cooperate to maintain stable temperatures for the delicate developing larvae.

 But how do honey bees know when it’s too hot for the larvae?

We placed single fanners (honey bees observed fanning) into a cage, and they we either 1) added a larva from the same colony directly into the cage with them, 2) added a larva but into a separate compartment where the fanner could not touch the larva, or 3) kept the fanner alone. We then heated the bee with the larva if there was one present, and recorded their fanning behavior.

When honey bees are alone, they rarely begin to fan. This makes sense: fanning is a very energetically expensive behavior, so it doesn’t make sense to do if there is no one around to fan. When a larva is present, however, a honey bee worker is more likely to fan, but only when they are able to have physical contact with the larva. If the larva is less than a centimeter away, but the worker is unable to touch it, the worker behaves as if there is no larva and rarely fans.

What could be the cue that larvae are giving off? Brood pheromone is a well known pheromone that honey bee larvae produce (Pankiw et al. 1998). It tells the workers whether the larvae are hungry or not, so it may tell the workers if the larvae are too hot. We found that being heated in the presence of brood pheromone did not increase fanning behavior. There are many other pheromones that could be telling the workers the larvae are overheating, but it does not seem to be brood pheromone. While we know that workers know when larvae are hot, most likely from having physical contact with them, we don’t know what the larvae are doing to let the workers know they are too hot.

Honey bees must actively monitor nutrition, infection, and temperature when rearing their babies. Workers manage their colonies very well, as thousands of workers care for the queen and hundreds of babies. For all of my friends having children, I am glad thermoregulation is one less thing they have to worry about.

References

Himmer, A (1932) Die Temperaturverhaltnisse bei den sozialen Hymenopteren. Biological Reviews, 7(3), 224-253.

Groh, C, Tautz, J, & Rössler, W (2004). Synaptic organization in the adult honey beebrain is influenced by brood-temperature control during pupal development. Proceedings of the National Academy of Sciences of the United States of America, 101, 4268-4273.

Kühnholz, S & Seeley, TD (1997). The control of water collection in honey bee colonies. Behavioral Ecology and Sociobiology, 41, 407-422.

Bonoan RE, Goldman RR, Wong PY, Starks PT (2014) Vasculature of the hive: Heat dissipation in the honey bee (Apis mellifera) hive. Naturwissenschaften 101:459–465.

Pankiw T, Page RE, Fondrk MK (1998) Brood pheromone stimulates pollen foraging in honey bees (Apis mellifera). Behavioral Ecology and Sociobiology 44:193–198.