A Role for Octopamine in Honey Bee Division of Labor
David J. Schulza, Andrew B. Barrona, Gene E. Robinson
Social insects thrive because of their division of labor. In honeybees, this division of labor takes different forms as the bees themselves age. As they get older, honey bees perform different subscribed tasks(Winston 1987). This change in tasks is called behavioral plasticity but the underlying processes the allow this plasticity are yet undiscovered. This paper endeavors to discover the role of amines in the switch between in-hive work and foraging.
honey bee in flight: http://ncpedia.org/symbols/insect
Honey Bee Behavioral Plasticity
The onset of foraging behaviors is much like puberty. Once a bee exhibits foraging behavior, it does not return to in-hive tasks. This time in the life of a honey bee is when the endocrine and exocrine glands are developed. Biogenic amines are modulators of neural function(Evans 1980; Erber et al. 1993). Octopamine and serotonin in the antennal lobes of the bee brain are known to be associated with foraging. the antennal lobe is the olfactory processing center of the brain. Octopamine, and not serotonin, is responsible for the transition from in-hive work to foraging behavior. Short term changes in behavior have been observed by injecting octopamine into the brain.
Chemical Structure of octopamine
image source: http://upload.wikimedia.org/wikipedia/commons/4/47/Octopamin.svg
Octopamine acts as an activator of foraging by modulating responsiveness to foraging-related stimuli.
Experimental set up
Levels of amines were measured in the dissected regions of honey bees and determined to be associated with tasks, by way of HPLC analysis. Second, colonies were treated with amines and observed to see if a change in foraging behavior arose. The treatment of these colonies was done by mixing the amine with 50% sucrose solution and the foraging bees carried it back to the hive.
Octopamine concentration was most associated with task in the antennal lobes of the bee brain. octopamine was found in high levels in foragers and lower in nurses no matter the age of the bee. In the neighboring lobes, however, octopamine was more associates with ag and not behavior. this indicated that there is modular and limited behavior in these two different brain regions in respect to octopamine.
When colonies were treated with octopamine, earlier onset of foraging was seen in younger bees. The levels of octopamine remained high when a forager returned from a flight, suggesting that this is a permanent change that will not be undone, but will maintain the foraging state.
image source: http://animals.nationalgeographic.com/animals/bugs/honeybee/
Foraging itself does not turn on the octopamine production in the brain, but rather the octopamine makes the bee susceptible to the stimuli that lead the bee to forage.
It is unknown how juvenile hormone and octopamine interact but it is suggested that octopamine must act downstream from juvenile hormone. It is also clear that juvenile hormone regulates octopamine levels. This means that foraging behavior is not simply a step in the process of growth to adulthood, but requires other cues, such as octopamine, to start this behavior.
The next level of analysis will be to determine precisely where and how octopamine acts in the nervous system to coordinate this complex social behavior.
Strengths and weaknesses of this paper
The strengths and weaknesses of this paper stem from the same source. While it is good that they can to controlled experiments with these foragers to take octopamine to empty hives, it seems that they miss some of the social interactions that could lead to foraging behavior. overall, this was a very interesting study that may lead to further investigations into the role of octopamine in the neurochemical pathway that leads to foraging behavior.
Winston, M.L. (1987) The Biology of the Honey Bee. Harvard University Press, Cambridge, MA.
Evans, P.D. (1980) Biogenic amines in the insect nervous system. Adv. Insect Physiol., 15: 317– 473.
Erber, J., P. Kloppenburg, and A. Scheidler (1993) Neuromodulation by serotonin and octopam- ine in the honeybee: behaviour, neuroanatomy and electrophysiology. Experientia, 49: 1073– 1083.