Malka, O, Katzav-Gozansky, T, Hefetz, A. (2009) Uncoupling fertility from fertility-associated pheromones in worker honeybees (Apis mellifera). Journal of Insect Physiology, 55, 205-209

Chemical signals, here as fertility associated pheromones, are important to social insects, such as honeybees, in that they are of interest to both the signaler and receiver regarding reproductive skew and dominance. The authors of this paper experimentally uncoupled fertility, by inhibiting ovarian development, and pheromone production as a means to support or refute four different hypotheses regarding pheromone production and ovarian development and the coupling of the two.

The honeybee has very complex communicative signals that serve to affect worker fertility and sterility in a number of ways. The authors primarily examined two glands involved in fertility, the mandibular gland, which inhibits ovarian development in workers and also serves to establish a reproductive hierarchy among queenless workers, and the Dufour’s gland, which produces esters that serve as a reliable signal of fertility and can trigger aggression among reproductively competing workers.

For this study queenless callow honeybee workers were either treated with methoprene with mineral oil, which inhibited ovarian development, or mineral oil alone or neither, which represented the two controls. After 14 days they were sacrificed and their ovaries removed, measured and rated on a scale from 1 to 3, with 1 being undeveloped and 3 being greater than 1mm. Both of the glands were also removed and examined for presence and amounts of chemical compounds.

The methoprene treated bees showed a lack of development of the ovaries, as was expected. The authors thought that there might be inhibition of the Dufour’s gland producing esters in the treated bees, that had no or very little ovarian development, but instead they found that there was no qualitative difference in the treated versus control bees and actually found an increase of esters in the treated bees. They found similar results for the mandibular gland, and found increase in glandular hydrocarbons for both treated and control groups. The authors believe that the presence of fertility pheromones despite the lack of ovarian development in the treated bees, demonstates that they can be uncoupled and are therefore independent.

These findings support their hypothesis that pheromone production and ovarian production are triggered by a common signal but have different regulatory systems. They may have evolved independently but have been favorably selected as being in the best interest for both the signaler and the receiver, since they constitute honest signals of ovarian development which is necessary for social insects to establish reproductive hierarchies and domiance.

This topic of pheromone production in bees which signals fertility-related behavior is a topic that was discussed in the lecture about chemical receptors. The pheromones released by the different glands in the bees are produced by one bee with the intent to send an honest signal, for example fertility dominance, to the receptor bee. The production of complex and numerous pheromones is important for social insects who use chemical signals to transfer information, as can be seen by their number of pheromone producing glands.