pesticides pollinator threats

Mason bees are not the answer

I see a lot of posts and tweets that seem to point to the mason bee as the answer to pollinator decline. Sure, I like mason bees, and here in the Pacific Northwest they have the added advantage of being native. However, we don’t yet have a consensus about what is killing the honey bee. If my hunch is correct—if the honey bee is declining due to contaminated pollen—then the mason bees (and other wild bees) are in danger as well.

Pollen is the primary protein source for these animals and it is critical for their health, growth, and development. In honey bees the pollen is first digested by the nurse bees and then fed as glandular secretions to the larvae. In mason bees, the pollen is left in the form of a provision which is eaten directly by the larvae as it grows. In either case, if that pollen is carrying pesticides, the larvae may die. Or—and this is harder to determine—the larvae may grow into adults that have abnormalities. These abnormalities may be morphological, behavioral, or reproductive. Any of these could cause the young bees to die or be unable to reproduce.

It is simplistic to think mason bees are the answer to the bee problem. By all means we should be encouraging mason bees—and all wild bees—by providing habitat, wildlife corridors, and continuous and varied forage. But we need to keep on top of legislators and demand testing of pesticide levels in pollen, testing of sublethal effects of pesticides, and pesticide regulation that is determined not only by toxicity to adult bees but to larval bees as well. The larvae are the ones most likely to be poisoned by pollen and we will have no bees—of any variety—if the larvae can’t survive.

We can’t expect the amount of pesticide in our environment to decrease until we demand organic food, demand that public lands not be sprayed, and until we stop using pesticides on our gardens, lawns, and homes. By pesticide I mean all the “cides“—insecticide, fungicide, acaricide, rodenticide, herbicide—it makes no difference. They all kill life, and many of them interact with each other, becoming even more toxic in the process.


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  • While modern “parts-per-billion” and “parts-per-trillion” measurement techniques reveal a wide range of pesticides and herbicides at trace levels in pollen, wax, and bee bodies, the good news is that these are trace levels, not above what one would expect to find.

    Better yet, these trace levels are well below the “NOEC” (No Observed Effect Concentration) levels for those pesticides where such studies have been done, so the claims of sub-lethal effects or cumulative effects are easy enough to settle. Maryann Frazier of Penn State wrote a very coherent report about exactly this issue What Have Pesticides Got to Do with It? (American Bee Journal Jun 2008).

    The problem with “pesticides” and bees is that a small number of large beekeepers chose to use off-label chemicals as miticides, and chose to overdose their bees. The only chemcials found at levels of concern to bee health have been these miticides, proving that the beekeepers blaming pesticides are suffering from self-inflicted gunshot wounds to the foot.

    The actual problems that are killing beehives are the exotic invasive pathogens and diseases brought from (mostly) Asia by unregulated world trade in un-inspected container shipments, so the cause of “CCD” is your flatscreen TV and all the other cheap imported stuff you bought.

    So, mason bees are not the answer, and pesticides are not the problem.

    And mason bees are not pollinating the full range of crops pollinated by honey bees, and likely never will. They are useful in a few crops, but no native type of bee has ever shown to be as amazingly useful as the honey bee in real-world agriculture.