Pesticides. A difficult topic to navigate indeed. Precisely what should be done about them (if anything) is a charged debate with many layers, and here I will try to peel some of the most prominent. The tl;dr version: it’s complicated. I’m not talking about overuse of pesticides – that is a separate issue. In developing nations, overuse of pesticides is an ongoing problem stemming largely from lack of education and regulation. No, what I’m addressing here is the homegrown opinion that pesticides are plain bad news.
Learning from our mistakes: DDT
Pesticides are an old topic on the hive mind. Right on the heels of Silent Spring (1962) was a timely realization about the risks of then-popular DDT (dichloro-diphenyl-trichloroethane). Today, we know that DDT is dangerous – it travels long distances via global air cycles and bioaccumulates in the fatty tissue of animals over time. That means that DDT concentrates in long-lived, blubbery beasts (one could argue that humans fall into this category) becoming far higher than the ‘safe’ levels in the surrounding environment. As an endocrine disruptor (i.e. a hormone mimic), this causes reproductive abnormalities. DDT contributed to the plight of bald eagles and some of the insects DDT targeted began developing resistance as early as the 1950s. The list goes on. There was a time when we just didn’t have the data to indicate these consequences, so it’s understandable to look at today’s war on pesticides and wonder if we are again awash with naiveté.
The rise of neonics
After DDT was condemned, other synthetic pesticides became commonplace (organophosphates, carbamates and pyrethroids) until neonicotinoids (‘neonics’ for short) arrived on the scene. Neonics offer some benefits over the other pesticides, namely, they don’t bioaccumulate, they’re less toxic to mammals and birds, and are amenable to more efficient application methods that use less pesticide than traditional foliar sprays. Neonics are now the most commonly used pesticides in the world, although it’s not clear how much of that is driven by top-down pressure from suppliers and how much is demand from farmers. In the US, the switch to neonics (very) roughly coincided with increased honey bee health problems, so the pesticides were promptly blamed. However, in countries where the switch occurred around the same time (Australia and Canada) the same trend was not observed, which doesn’t fit the argument that they are entirely, or even predominantly, to blame for our pollinators’ health problems any more than their predecessors.
So how toxic are they, really?
Neonics are toxic to bees – they are insecticides after all. The golden pesticide would be one that kills pest insects while leaving beneficial insects unscathed, but unfortunately, such a compound doesn’t exist (actually, that’s not quite true – it does exist, but you are probably more familiar with a different name: GMOs). For neonics, as for any pesticide, there are trade-offs between gaining pest control and harming beneficial insects.
When pesticides are scored for toxicity, the most common method is to compare “LD50” doses – that is, the dose at which 50% of treated individuals will die within a defined period (usually a few days). If this seems like a crude experiment, it is – this test only captures “acute lethal toxicity.” It’s the traditional test and there are valid criticisms about it, especially considering the now-thick catalogue of pollinator ailments caused by longer, lower-dose exposures (like behavioral changes or reduced queen longevity). In toxicology terms, this is called “chronic sub-lethal toxicity.” While calculating the LD50 is trivial, investigating chronic sub-lethal effects takes more time, creativity, and funding – especially for field trials – so for older, non-neonic pesticides it largely has not been pursued.
Momentum from the outrage over neonics was picked up by scientists, launching a greater volume of research on how neonics affect pollinators than for any other class of pesticide. Some of the research is sound and innovative while some is misguided, but either way a benefit of this is that we now have a better idea of the kinds of sub-lethal effects that are possible (like how season, species, and caste all factor in to the results). Before, this wasn’t given much thought. However, the pivotal piece of data that is still missing is the relative toxicity of different pesticides; that is, how neonics measure up to organophosphates, pyrethroids and carbamates. Those pesticides are not such hot-button issues, so comparable research on them has been extremely lacking, despite being (what should be) an integral component of the neonic debate.
Unfortunately, some studies describing neonic toxicity didn’t use doses that accurately reflect what bees are exposed to in the field. Part of this was because it was hard to know exactly what the bees’ exposure levels were and it wasn’t clear how fast the chemicals broke down once brought in the hive (i.e. how does accumulation balance with chemical breakdown?) but we have a much better idea of this now. Not all the dosing inaccuracies were honest, though; some researchers flat-out used the wrong dose in their experiments – the now-infamous paper by Chensheng Lu is a prime example of that. When describing their experiments, the authors claim that “this dosage is far below the oral LD50 […] for clothianidin and imidacloprid,” (two prominent neonic pesticides) which it is; however, comparing their dose to the LD50 is disingenuous because we know the LD50 is far higher than the ball park of what bees actually experience in the field. So, although their dose was below the LD50, it was still one or two orders of magnitude higher than what bees regularly encounter. Not all pesticide experiments have been so off the mark, though, and it’s unfortunate that ones like that were published (and given so much press) because it further muddies the already-turbid waters.
The Lu paper was published in 2014, but Jeff Pettis and the rest of his team quickly balanced it with a detailed report the following year. They selected a range of imidacloprid doses that reflect the amounts honey bees are likely exposed to in the field, as best they could estimate depending on the crop, application method and known routes of exposure. The introduction to their open-access paper is a refreshing summary of what we know and don’t know – no embellishment, just the facts. Their experiments and data follow the same rhythm; they found that over the course of three years, the lowest neonic dose – reflecting the exposure expected from seed treatments of corn, sunflower or rape – caused “negligible effects on colony health.” The higher doses – corresponding to what might be found in a blooming pumpkin patch treated by drip irrigation – caused some queen failure and subsequently lower overwintering colony survival. This kind of well-balanced, long-term field study gives us the clearest picture of what application levels strike the best balance to benefit both farmers and beekeepers.
Peter Jenkins, the attorney representing the Center for Food Safety (one plaintiff in the recent Ellis v. Housenger case) wasn’t wrong when he said, “Vast amounts of scientific literature show the hazards [neonicotinoids] pose are far worse than we knew five years ago” (as reported by Susan Salisbury). Jenkins and the rest of the team recently won a four-year battle against Syngenta, Bayer and the EPA over issuing ‘unlawful’ pesticide regulations. However, while it’s fair to say that we know more now about neonics than we used to, we also have constructive routes forward for how to use them responsibly. Until someone shows that there’s an alternative pesticide that is equivalently effective against pests but poses less risk to pollinators, it’s not very useful to blanketly decry neonics. We should be backing up statements like “the hazards of neonics are worse than we thought” with constructive solutions, because full-on banning one pesticide or another is unlikely to satisfy everyone and further polarizes the discussion. If we know which pesticides, which doses and which application methods are safest to use in specific circumstances, then we can use them responsibly to maximize yields and minimize risk.
Can agriculture, bees and pesticides coexist?
The war on pesticides is sometimes misconstrued as a war on agriculture, but it’s not: when done right, the two industries are mutually beneficial. I’d like to reflect on the sentiments of a paper that came out this April in the Journal of Economic Entomology – the authors describe how colonies in landscapes with moderate to intense agriculture had higher brood production and colony weights, but suffered higher queen losses late in the season (which agrees with the Pettis study). However, colonies in less agriculturally intense areas (either urban or park) had a higher incidence of starvation. Of course, agriculture also benefits from having more honey bees working the field. Granted, the scale of this study was quite small for a field trial (just 16 colonies were analyzed in total) but it isn’t a one-off: it is consistent with another larger field study8 and is yet another illustration of the pervasive risk-benefit conundrum. These studies demonstrate there is certainly incentive for farming and beekeeping coexistence where both sides clearly benefit.
Instead of focusing on whether one chemical or another should be banned, we should focus on which option is safest to use in the given scenario and how to use it responsibly. Since we currently haven’t studied the relative safety of neonics compared to older generation pesticides, let’s focus on the latter. A reasonable definition of “responsible use of pesticides” might include only using pesticides when they’re needed. Aesthetic use in urban settings constitutes irresponsible use, in my opinion, since there is no measurable need for it and overuse is pervasive (if a little is good, a lot is better – right?). Large scale, prophylactic seed treatments may seem irresponsible at first, but in some cases this is probably actually the best approach. Seed treatment uses anywhere from 4 to 20 times less pesticide per plant compared to foliar spray. So, as a conservative estimate, if no one used prophylactic seed treatments but one in four farms required foliar spray down the road, this outcome is no better than if everyone used the seed treatment. Especially when planting pest-sensitive crops in geographic areas that have traditionally high pest levels, prophylactic seed treatments make a lot of sense. In other areas, where the threat of pests is unpredictable or non-existent, the most responsible approach may be to monitor the pest load and apply pesticides when a predefined threshold is reached – that is, the same integrated pest management (IPM) principles that many beekeepers are now familiar with for dealing with Varroa destructor and Nosema spp. According to Dee Ann Benard’s 2015 Canadian federal report,9 which took the pulse of what farmers thought about IPM, not surprisingly, “cost and time were identified as barriers to the adoption of these techniques.” I will not pretend to know the stresses of being a farmer, but like most problems in economics, these concerns are probably surmountable with the right incentivization.
Communication between beekeepers and farmers about the timing of sprays is another great example of using pesticides responsibly. The Canadian Honey Council and CropLife Canada have teamed up to great a mobile app (called “BeeConnected”), which is designed to make it easier for famers, contractors, and beekeepers to broadcast when and where pesticide applications are scheduled. It’s a great example of industries working together to minimize risk. I am not sure if the app works in the US or not – if you’re interested, perhaps some of you could try and if it is not compatible with US operations, send the developers a note at email@example.com to show them there’s demand for their technology in your area. Honey bees are just one instrument in the orchestra, though, so the other risk-minimizing strategies are still every bit as important for native pollinators.
Consider the opposite
The EPA banned DDT in 1972. However, even today there are some instances where using DDT is permissible because every scenario requires its own risk-benefit analysis. In developing countries where the risk of contracting malaria is extremely high, DDT is permitted as a tool for mosquito population control. The benefit of suppressing the malaria-transmitting mosquitoes outweighs the risk of DDT exposure. That’s not to say that DDT is the best solution for the problem (maybe, ahem, neonics are a safer approach), but it reminds us to be mindful of the nuances at the intersection science, economics, and society. Sweeping changes might be the most automatic reaction, but it’s rarely the best solution.
This article appeared in the June 2017 issue of American Bee Journal.