There’s growing evidence that agrochemicals other than pesticides are impacting honey bee health. Last January an article published in Scientific Reports described how a supposedly biologically inert spray (called Sylgard, an adjuvant normally used to enhance the effect of other spray components) affects honey bees in unexpected ways. This is concerning because since it wasn’t thought to be harmful, Sylgard is not closely regulated by the federal government in Canada or the States. In their study, Fine et al. reared honey bee worker brood in the lab and exposed them to either nothing, Sylgard, black queen cell virus (BQCV) or a combination of the two. As expected, BQCV caused significant mortality (23% more than the untreated brood), whereas Sylgard caused minimal mortality (4%) on its own. However, when BQCV and Sylgard were combined, mortality jumped by a factor greater than the additive effect of the two separate treatments (up to 44%). In other words, they interacted synergistically. How Sylgard (or other similar sprays) interacts with other pathogens – if at all – has yet to be investigated. Sylgard might not be as big of a concern in Canada as it is in the States (it is used heavily during the California almond pollination); however, there are still some Canadian operations where it is employed.

There is growing evidence suggesting that adjuvants are not as safe as once thought, but interpreting these toxicity studies for the real world is difficult because each adjuvant has a different toxic dose. How the toxic dose relates to the real dose is what’s important. Assuming the recommended dose on the label is what’s applied in the field, it’s still not obvious what the dose is that pollinators receive because some adjuvants deter the pollinators from interacting with the plant in the first place (of course, this is also a problem for pollination!). Other factors like time of day and weather can also impact the real exposure that pollinators receive. The real dose could easily be far less than the application itself. It is probably not reasonable or necessary to outright ban these compounds, but the hints at toxicity are worth investigating in more depth to either 1) prevent them from being unduly labeled as the new cause of all the honey bees’ problems or 2) if they are causing significant harm, allow us to adopt better strategies for minimizing risk. Until we know what their real impact is, it is would be prudent to improve communication between farmers and beekeepers about timing of sprays – like what is already being done with some pesticides – to minimize exposure when we can.

Fungicides are another group of agrochemicals which may be affecting honey bee health more than we once thought. Coincidentally, these are also heavily utilized during almond bloom. Unlike pesticides, we wouldn’t necessarily expect fungicides to be toxic to honey bees since there is a huge evolutionary divide between fungi and insects (they are not even in the same kingdom in the tree of life) and what kills one may very well be tolerated by the other. However, some recent research by Fisher et al. shows that some fungicides (Iprodione 2SE Select alone or together with Pristine and Quadris) can increase honey bee mortality, especially late in the fall. While this study simulated a somewhat worst-case-scenario of honey bees being sprayed when they are foraging on the crops during a field application, it does alert us to some potentially underappreciated effects of fungicides and the significant seasonal dependence of the honey bees’ ability to deal with these challenges.

This article appeared in the Spring 2017 issue of Bee Scene.

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