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Hormones are produced in glandular or, more commonly in insects, neurosecretory cells and act on susceptible cells within an individual bee. They may change the permeability of cell membranes and block or enhance the production and passage of neuro-transmitters. They can breakdown very quickly or can persist for a time. Pheromones are secreted externally from glandular cells, and target specific receptive cells in the sense organs of other bees. These organs, in turn, produce neuro-secretions which act on organs within. The production of hormones can be governed by other bees, by forage, and by the environment.
One of the most important group of hormones in bees are the juvenile hormones, which influence aging and development. Paradoxically, the more juvenile hormone there is, the more mature the bee. Increasing the amount of juvenile hormone in young bees will, amongst other things, promote early foraging behaviour (Robinson & Huang, 1998). The level of juvenile hormone is determined by the season (Buhler, 1983), by the queen (Pankiw, 1998) and by brood (Huang & Robinson, 1996).
Brood pheromones are produced by all stages of brood, although their composition changes. They encourage various nursing behaviours, pollen foraging, brood recognition, and cell capping, but inhibit ovary development and queen rearing, and lower juvenile hormone production (Le Conte, 1999). Some are received by contact with open brood while others are more volatile. Queen pupae inhibit cell construction (Boch, 1979, Free & Ferguson, 1982). The fact that both queen and brood pheromones suppress work ovary development means that workers will not begin laying their own eggs if their queen is lost, unless her brood is also lost.
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Foraging and swarming
Think that’s all there is to vitellogenin? Dr. Amdam got together with California’s Dr. Rob Page (Nelson, et al. 2007), who had previously developed a pollen-collecting line of bees. Page had found that bees genetically biased to collect pollen were characterized by high levels of vitellogenin. Together the researchers discovered that the vitellogenin titer developed by a worker bee in its first four days after emergence, affected its subsequent age to begin foraging, and whether it preferentially foraged for nectar or pollen! If young workers are short on food their first days of life, they tend to begin foraging precociously, and preferentially for nectar. If they are moderately fed, they forage at normal age, again preferentially for nectar. However, if they are abundantly fed immediately after emergence, their vitellogenin titer is high, and they begin foraging later in life, preferentially collect pollen, and have a longer lifespan. This scenario certainly makes sense—a starving colony would want skip raising brood, and send out foragers to gather as much nectar as they could. A fat colony would want to rear brood and build protein reserves in order to swarm.