Here are a few examples. Among the barriers to a sustainable yield of bees are a variety of larval mortality factors that include pollen balls, chalkbrood disease, parasites and predators, second generation, and proportion of females. Take the last factor, proportion of females. Anyone familiar with the biology of tunnel nesting Megachild bees is aware that sex ratios are frequently biased toward males in these bees. So, our ability to alter the sex ratio of these bees is limited.
Canadian growers use the deeper boards.
Because pollen balls are worse in the Northwest than in Canada, so it takes longer for the boards to dry in order to be punched out. They are deeper than solid boards, and don t need to be punched out, although they may be more expensive. A reduction in pollen balls would not only increase the percent live bees directly, but would also allow growers to use deeper nest blocks and thus get a higher proportion of females. There is evidence to suggest that pollen balls, chalkbrood, and parasites are high because so many bees are being introduced into alfalfa seed fields. If numbers of bees were reduced, say if half the bees were introduced into fields than are currently used, mortality from all of these problems might be reduced, both because there would be more flower resources available to the bees, and populations in each shelter would be reduced.