The honeybee crisis continues; one-third of all colonies die each year around the globe, and we know why. It’s not one factor, and our deepening understanding of the multiple stressors that are killing bees has clarified the extent of our human responsibility in this tragedy.
A considerable body of research has shown that pesticides are one set of factors that interact to harm adult bees, either through simple additive toxic effects or synergistically with each other so that their effects are considerably worse than what would be expected from just adding them together. Further, pesticides often interfere with bees’ immune systems, amplifying the effects of bee diseases.
And, there are well over 100 pesticides found in a typical beehive, some applied directly by beekeepers but most brought back to the hive by foraging bees. Together, this array of poisons to which bees are exposed has created a toxic colony environment.
Now a new study from Pennsylvania State University has shown that interactions between chemicals affect larval bees as well as the previously studied adults. This project examined impacts of four commonly used pesticides on honeybee larvae, as well as testing an inert ingredient used to formulate pesticides that previously was untested but thought to be innocuous to bees.
Two of the pesticides tested, fluvalinate and coumpahos, are regularly applied by beekeepers to kill the serious mite pest varroa. The other two are farmer-applied pesticides, the fungicide chlorothalonil and the insecticide chlorpyrifos, both with widespread use in agriculture. They tested each compound alone and in combination with the others, at doses reflecting typical pesticide residues larval bees would be exposed to when fed protein-rich pollen that has been processed into larval food by adult bees.
The results indicated that larval stages are considerably more susceptible than adults, and that generally the pesticides were worse together than alone. Sometimes two or more pesticides simply showed additive impact, but for some the impacts were synergistic, indicating an interaction that amplified their toxicity.
They also examined an inert ingredient commonly used as a carrier for pesticides, nicknamed NMP, that showed high toxicity to larvae.
The simplest conclusion of the study was that we are not testing pesticides widely enough for regulators to make informed decisions about approving compounds. The authors concluded that mixtures of pesticides and inert ingredients must be tested as well as the single compounds, and that both adults and larvae need to be studied to garner realistic data about impacts.
They also affirmed what most of us in the bee world believe: Bees are not dying because of one thing, but a combination of causes including pesticides, diseases, poor nutrition due to reduced diversity of nectar and pollen-producing flowers and other factors.
Their study has profound implications for what we need to do to protect bees, as well as for our own human health.
Bees will continue to die until we restructure agriculture. The necessary reforms are significant, but would have numerous environmental benefits as well as providing better health for bees: polycultural farming rather than extensive single cropping, increased plant diversity in and around farmland and reduced pesticide use by farmers and beekeepers. It’s a big bit task, but we best begin soon, before the crisis deepens.
The demise of bees also calls to our attention similar challenges for human health. We, like bees, are exposed to hundreds of pesticides and industrial chemicals. These potential toxins have been approved by regulators based on exposure to single compounds rather than to the mixtures to which we actually are exposed. And, tolerance levels are based on predicted effects for adult exposure rather than for children, who are considerably more vulnerable.
Also, our own poor nutrition due to high sugar and fat diets and over processed, nutritionally incomplete foods is reminiscent of the limited forage that bees must now depend on to meet their dietary needs.
In other words: we’re not so different from the bees, and their fate may well be the harbinger of ours.
For more detail see:
Wanyi Zhu, Daniel R. Schmehl, Christopher A. Mullin, James L. Frazier 2014. Four Common Pesticides, Their Mixtures and a Formulation Solvent in the Hive Environment Have High Oral Toxicity to Honey Bee Larvae. DOI: 10.1371/journal.pone.0077547