Since 2010, I and my team through our contract research company has conducted a variety of studies of habitats, pollination, and croplands.Some of our observations:
1) Crops that used to produce copious amounts of nectar and/or pollen no longer provide much, if any, and what is available to the bees is often significantly reduced in sugar and protein. Plant geneticists and growers keep selecting for plant traits that increase yields or market value while ignoring pollinator requirements for nutrition, including whether the plant is any longer attractive to bees.
2) Many pesticides have an unlisted effect - they repel bees, and the effect may be additive when mixtures of pesticides are applied (e.g., mixtures of fungicides).
3) Habitat loss can occur suddenly, such as widespread increases in acreages due to government programs promoting alcohol fuels (e.g., corn belt, where one sees little or nothing but corn, right up to the edge of paved roads, for miles and miles), or as happened in MT, where northwest of Great Falls, large numbers of alfalfa fields were changed to barley when Budweiser set up giant granaries.
As several have mentioned, lots of factors contribute to habitat loss. But no one is talking about the real issue: carrying capacity! I've traveled the world, conducting research and visiting beekeepers. I always ask about average and peak honey crops. More times than I would have imagined, the beekeepers unknowingly exceed carrying capacities. Some examples,
1) In an area along the Columbia River, north of the Tri-Cities of Washington, renowned for its honey yields, beekeepers told me (1980s) that honey crops had significantly fallen off in the previous years with no apparent reason. Each beekeeper I interviewed said the same, and each knew of another beekeeper in the area. I looked for apiaries to sample for radionuclides - this area was west of the Hanford site nuclear reactors. I found several beekeepers, each hiding their apiaries behind hills, haystacks, or low areas. There were at least six beekeepers, with over 1,000 colonies in a square mile area!
2) In the USA, the average size of commercial apiaries in many states known for high honey yields is 24 to 30 colonies per apiary, with at least a mile, preferably two, between apiaries. That's easy to track in MT, which has a regulated 3-mile separation zone between different beekeeping businesses, with over 5,000 registered locations. But most states lack a separation zone so that anyone can put any number of colonies, regardless of ownership, anywhere. That leads to obvious conflicts. If one beekeeper has X number of colonies on a good forage location, and a second beekeeper drops X number of colonies on the other side of the fence, don't be surprised if the production of each drops to 50% of the prior output when only one beekeeper had an apiary at the location.
3) In some US states, I was surprised that the typical number of colonies per apiary was 100 to 200! So far, I've not seen any of those areas listed among the top honey-producing states. I always ask why, and the answer is that that's what dad, granddad, and great-granddad did. If you look at the books from the early 1900s that describe the honey plants and yields per state, you'll find that these same states have been putting 100-200 colonies at each apiary since the 1920s, and the state yields have hardly changed.
Given this, finding peer-reviewed research studies on carrying capacities for honey bees is challenging. There's a recent one for urban beekeepers in Switzerland, a couple from the Middle Eastern countries, and one from Africa. If anyone on Bee-L can provide citations to research studies about honey bee carrying capacity, please post the citation so we can read and discuss.
Without clear guidelines, I suggest that anyone in an area where more than 30 colonies are placed per apiary do some testing. It may take a few years, but its possible that honey production may remain the same or increase using fewer colonies. Fewer colonies, higher production, more profit.
However, in one case, the beekeeper didn't care - all that was desired was enough nectar and pollen to maintain or increase the number of colonies for pollination rental.
Jerry
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