Sure, honey bees are important. They’re worth about $1.6 billion annually to U.S. agriculture. But take the blueberry plant, for example: southeastern blueberry bees, bumble bees, carpenter bees, orchard bees, Bradley’s andrena bee, and many others lend a “tarsus” in pollinating flowers. Together, all these “other” pollinators are more important than honey bees economically (by about $5 billion) and ecologically (enhancing productivity and stability).
While honey bees are the center of public attention—partly because they’re dying from Varroa destructor mites, the Nosema apis fungus, and insecticides—native bees modestly continue to pollinate in the face of similar environmental challenges.
However, the stingless bee Friesella schrottkyi (Hymenoptera: Apinae) made headlines this week because of new research by Rodrigues et al. identifying copper sulfate-containing leaf fertilizers as mind-altering and lethal when consumed by F. schrottkyi. (Image credit: Sylvia Maria Matsuda, Laboratório de Abelhas)
Wait a second. The research article only investigated the effects of certain leaf fertilizers on one species of stingless bee. Our friend F. schrottkyi’s only been famous for a week, and already we’re speculating and generalizing.
A key point to this research is in understanding the differences in pollination behavior and agrochemical toxicity among bee species. And stingless bees are not a single species, but rather a very diverse group in and of themselves. The effects of biopesticides, fungicides, and other agrochemicals on all kinds of bees (as well as other pollinators, and the surrounding ecosystem as a whole) is incredibly important.
So let’s take a quick look at what the Rodrigues et al. paper actually says:
- The authors are implicitly concerned about the effects of all agrochemicals (especially non-insecticides) on a wide diversity of native pollinators.
- Their research focused on Friesella schrottkyi and two commonly used fertilizers.
- A series of bioassays (experiments run in the laboratory, not in the field) assessed the toxicity of a micronutrient mix and a fertilizer containing 24% copper sulfate.
- The copper sulfate-containing fertilizer was surprising deadly when consumed, while contact exposure affected flight and foraging behavior.
- Consuming the micronutrient mix did not affect F. schrottkyi survival, but did reduce respiration rate.
- Copper, manganese, molybdenum, zinc, sulfur, and boron may all be involved in the toxic effects of leaf fertilizers on bees.
It’s important to take a step back and think about what this research really means. We should not be making broad conclusions, but we do need to ask questions about how other leaf fertilizers and other agrochemicals are affecting a wider spectrum of animals. While in a general sense it’s true that at high enough concentrations, all leaf fertilizers are probably toxic to all stingless bees, this conclusion is beyond the scope of the Rodrigues et al. article.
I also feel it shouldn’t come as a surprise to anyone that the heavy metals in fertilizers, administered orally or in high concentrations, have a negative affect on, well, any insect, plant, or animal. Heavy metals play an important role as cofactors for proteins and enzymes (think hemoglobin, in blood). But at higher levels, heavy metals start to interfere with enzymes, cellular structures, and even DNA.
The point is to take these broad ideas—like the stuff we think can be toxic, the pollinators we think are useful—and learn as much as we can about it, which is exactly what Rodrigues et al. did: figuring how and why a commonly used fertilizer affects one of their native bees. The best way we can preserve our ecosystems and protect our agriculture is to have detailed knowledge of how it works—and then we can ask even more questions and create new hypotheses about how stuff works.