Neonicotinoid pesticides (neonics, for short) have been a hot topic in popular media and scientific research alike. As Randy Oliver highlighted in the July issue of American Bee Journal, the number of scientific publications including “neonicotinoid” as a keyword has increased exponentially over the last decade. Last June, two high profile research articles were published simultaneously in the prestigious journal Science – one by Nadia Tsvetkov (who is in Amro Zayed’s lab in Ontario), and one by Ben Woodcock in the UK. They used two different methods to assess effects of neonics in field-realistic scenarios and both, unsurprisingly, reported predominantly negative effects. These investigations lay to rest the general criticism that neonic research uses unreasonably high pesticide doses, but they still don’t answer what is, in my opinion, the most critical question of all: Is there a better alternative? These publications do, however, provide valuable information on neonic toxicity in a large-scale, realistic setting.
An on-going problem in pesticide research is that it’s very difficult to know exactly how much pesticide an average honey bee colony is exposed to, despite knowing the dose and timing of crop applications. Weather, attractiveness of crops, surrounding forage sources, duration of exposure, and environmental persistence of the pesticide – among other factors – can all affect how high of a dose the honey bees receive. Tsvetkov et al. carefully calculated the abundance of neonics in 55 colonies located near neonic-treated corn fields in Ontario and Quebec. The in-hive abundance of neonics varied between 0 and 20 parts-per-billion between May and September, usually peaking shortly after corn planting. They also measured many other agrochemicals, including miticides, fungicides, herbicides and other pesticides, which can help researchers design future experiments on these compounds at real-life doses.
Tsvetkov et al. used the neonic abundance information to design a tightly controlled experiment aimed at deciphering the controversial question of the pesticide’s biological effects on colonies (e.g. impacts on social immunity and queen longevity). I was initially surprised to read that the researchers dosed their colonies by using neonic-impregnated pollen patties instead of exposing them passively in the field, as they did to determine the in-hive pesticide abundance in the first place. However, I suspect that they chose the pollen-patty method because it allows the dose to be precisely controlled over time while still being field-realistic. They found that the treated colonies had reduced worker and queen longevity as well as deterioration of hygienic behavior – one important form of social disease resistance. All three of these results are consistent with previous research on this class of pesticides, the main difference being the scale and undeniably realistic setting.
Woodcock’s experiment was slightly different – he opted to use the most realistic exposure method of them all: passive exposure by placing colonies in neonic-treated oilseed rape fields. The scale of this experiment was even more massive than Tsvetkov’s, with 33 field sites in the UK, Germany and Hungary, and three bee species (Apis mellifera, Bombus terrestris and Osmia bicornis – a solitary species) examined. They measured a whole suite of colony parameters, including worker population, abundance of all brood stages, food stores, winter survival, hive weights, and others. Most of the measured parameters did not change significantly between the treated and untreated colonies; however, some key parameters did: honey bee worker population and overwintering survival, as well as B. terrestris queen production and O. bicornis egg production.
Importantly, these metrics were not significant across all countries. Colonies in Germany were largely unaffected, whereas UK and Hungarian colonies suffered. In fact, the only significant effects on the German colonies were positive – in other words, the colonies located in neonic-treated rape fields did better than the control colonies. It’s not clear whether this is because of differences in land use management, climate or some other factor, but it does suggest that there could be ways to use neonics that does not harm bees – domestic or otherwise.
I think one of the most interesting findings in these two papers is that, counterintuitively, the neonic residues found in the colonies appeared not to come from the crop that was actually being treated. Tsvetkov analyzed the pollen sources in colonies that tested positive for neonics, and found that pollen from the treated crop (corn) was only found in a small fraction of samples. Rather, the pesticides seem to come from surrounding wildflower forage, which picked up the neonics due to their proximity and shared water sources. Similarly, Woodcock found that the most abundant neonic in the colonies was one that wasn’t even applied to the rape fields where the colonies were located.
All these findings are interesting and informative, but a question continues to burn on my mind. If we were to switch to another type of pesticide, would that be any better for bees? To date, there has been no controlled experiment demonstrating that there are effective, safer neonic alternatives. This means that although most evidence suggests neonics are harmful, as it stands we have nothing else to turn to and it’s not practical (or even desirable, arguably) for all farms to go organic. Now, we need a route forward – hopefully, such a comparison will be the next big bee Science paper.