New Study on Bee Larvae Diet Does Not Reflect Real-World Pesticide Exposures
Why honey bee colonies are reportedly disappearing in the U.S. and Europe at faster rates today than previously is a question increasingly being asked. Every month, new reports emerge advancing theories on why this phenomenon – popularly known as colony collapse disorder – seems to be occurring.
Among the potential causes discussed have been viruses, disease-bearing mites, pesticide use, exotic predatory insects, reduction of worker bee foraging habitat and stress on colonies caused by farm-to-farm hive transportation as growers rent pollinators for their crops. All of these factors are believed to take a toll, but which are most important remains a subject of debate.
Recently, a new study (Zhu et al., 20141) has reported that pesticide exposures from pollen used to produce food for developing bees could, in extreme cases, be high enough to compromise their survival. A closer look, however, shows that the study in question was conducted under conditions very different from those in which bee larvae normally develop.
Additionally, for chlorpyrifos, which was one of the products evaluated, the exposures used were too extreme to reflect anticipated use. Here are some areas where this study’s results differ from real-world experience with chlorpyrifos.
- The larvae were fed an artificial diet with chlorpyrifos concentrations that would be expected to kill adult bees outright. (Exposure was ten- to 20-times the acute LD50.) This did confirm, however, that bee larvae are less sensitive to chlorpyrifos exposure than adult bees.
- The levels of chlorpyrifos used in the diet were greater than the residues found on pollen in a previous study. But bee larvae are fed and cared for by nurse-bees; they don’t eat much raw pollen. (Bee larvae in the study were fed by laboratory technicians outside their normal hive environment.)
- What bee larvae are fed is mostly protein, lipids and sugars from pre-digested pollen diluted with nurse-bee secretions and other components. In addition to the dilution factor for the pollen itself, digestive enzymes in nurse-bee stomachs could be expected to break down some pesticide before the larvae are fed.
- Another way of understanding difference between laboratory and field conditions with this study is that based on prior research by one of the study’s authors, the levels of chlorpyrifos fed to larvae were 8,000 times greater than average chlorpyrifos levels measured in the adult bees themselves. (I.e., 30 vs. 240,000 nanograms. Note: a nanogram is one billionth of a gram.)
Dow AgroSciences is committed to health and safety research furthering ongoing stewardship of its products. This study, unfortunately, overestimates exposures and cannot be used to project outcomes from anticipated product use.
1 Zhu et al., Four common pesticides, their mixtures ande a formulation solvent in the hive environment have high oral toxicity to honey bee larvae, January 2014, vol. 9, issue 1, e77547.
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