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NEW ZEALAND BEEKEEPER, JULY 2017
FACTORS SHAPING BEES’ REWARD PREFERENCES BURNING QUESTIONS Paul Burgess
This photograph shows a foraging bee on white clover (Trifolium repens) with an extended proboscis and khaki-coloured pollen load. The photograph raises a series of questions: is this a dual-reward worker? Just how well informed are we as to the controls on pollen versus nectar foraging? I imagine that internal influences (within the hive) and external opportunities are governing factors, but what shapes reward preferences within certain bees? Is there periodic switching or lifetime specialisation? And how prevalent is the collection of both nectar and pollen on a single trip? How do the various stimuli determine the quantity of pollen that is stored? Witness those colonies where an abundance of pollen encroaches on an otherwise convincing brood area and where newly introduced foundation becomes clogged as it is being drawn. Reply from Frank Lindsay Thanks for your question, Paul. I don’t have a degree of any sort, but I do have a curiosity and fascination with bees. These days you can find most anything on the Internet. You may also need a good library or access to a library with good bee books, such as the Apiculture New Zealand library in Ashburton administered by Linda Bray. I had it in my mind (I have either read it or heard it at a lecture) that the amount of nutrition fed to the brood while they are developing will stimulate those bees when they emerge to be either pollen gatherers or nectar gatherers. In a paper on PLoS ONE (Siegel, Freedman & Page, 2012), it’s actually the size of the worker’s ovaries that determine this function, and this relates to nutrition. According to Siegel, Freedman & Page (2012): In honey bees, ovary size (measured by counting ovarioles, the egg producing filaments of the ovary) is determined during larval development. Honey bee foragers with larger ovaries (more ovarioles), a reproductively associated characteristic, are biased toward protein collection compared to those with smaller ovaries (fewer ovarioles).
Photo: Paul Burgess.
(Amdam et al. 2006; Amdam et al. 2007). We conclude that the response to selection on honey bee pollen-hoarding behavior could be brought about by modification of early developmental processes. Trophallaxis, the exchanging of food and pheromones between bees, provides information about the colony’s energy status and food needs to the field bees. Some of these pheromones are given off by the young brood. The greater the amount of open brood, the greater will be the stimulus to gather pollen. The pollen-foraging bee packs the pollen into pellets that are carried back to the hive on the bee’s corbicula (pollen basket) and she deposits these directly into the cells around the brood nest. Pollen gatherers will keep doing this for as long as pollen exists in the
Amply fed bees will be pollen gatherers, while those with reduced nutrition will become nectar gatherers. Again, it depends on the needs of the hive. And as Amdam, Page, Fondrk and Brent (2010) reported: We found significant differences in JH [juvenile hormone] and ecdysteroids levels between high and low pollen hoarding strain bees during larval, pupal, and early adult life-stages. Our data strongly suggest that artificial selection on honey bee food-storage behavior acted on the genetic basis of JH expression to influence the larval retention process of ovarioles and the adults’ovary size. Ovary size may in turn dictate adult ecdysteroidogenesis. Correlations between worker ovary size, adult hormone sensitivity, and foraging biases are already established
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