Editor’s Choice 54:5 – Quantifying the collateral damage of neonicotinoid insecticides on bees

Issue 54:5’s Editor’s Choice is written by Sarah Diamond. The article chosen is Planting of neonicotinoid-treated maize poses risks for honey bees and other non-target organisms over a wide area without consistent crop yield benefit by C. Krupke et al.

As humans modify natural environments, we are witnessing the steady accumulation of unintended, cascading effects across biological communities. Biocontrol agents have escaped their intended targets and have harmed native flora and fauna. Habitat modification has fostered the spread of invasive organisms. Global changes in climate have led to the global redistribution of animals and disruption of entire ecosystems. In this issue of Journal of Applied Ecology, Krupke and colleagues explore the idea of unintended consequences of insecticide (neonicotinoid) treatment of crops on honeybee populations.

Image: Purdue Entomology

Neonicotinoids are a class of insecticides, and are commonly used to limit damage to crops by specific insect pest species. The potential for these insecticides to negatively impact “non-target” species has been recognized for some time (e.g., one recent example: Rundlöf et al. 2015, and references therein). However, previous studies concerned with the collateral damage of insecticide application generally examined how non-target species respond to neonicotinoids after exposure, leaving open the question of how non-target species were being exposed to the insecticide. The work of Krupke and colleagues bridged this gap in our knowledge: they empirically tested the route of honeybee exposure to neonicotinoids. Honeybees are a major non-target species in this system, and provide important ecosystem services through their roles as pollinators. The results of this study suggest a complex mechanism of exposure for honeybees: neonicotinoid-treated crop seeds release neonicotinoid into the air during the planting process, which effectively generates a pesticide-laden dust that is deposited downwind of the site of the original agricultural application, where non-target species like honeybees are found.

Image: Purdue Entomology


Across multiple sites and years, the authors quantified both the amount and the location of neonicotinoid deposition following the planting of treated crop seed. The authors combined a number of different methods, from experiments to the use of remote sensing data to isolate the mechanism by which non-target species could be exposed to neonicotinoids, and what the impacts of these compounds are on non-target species at the biologically relevant concentrations they encounter in the field. They found that foraging bees encounter lethal doses of neonicotinoid residues from planter dust within the range of deposition from agricultural sites, and that the concentration of neonicotinoids was highest downwind of the original application site. This pattern of deposition further supported the authors’ hypothesis that aerosolized neonicotinoid-contaminated planter dust was the mechanism by which non-target species were being exposed.

Beyond uncovering the mechanism of neonicotinoid exposure for non-target species, the authors also quantified the benefit, in terms of crop yield, under the application of neonicotinoid. Their findings here were rather surprising, and indicated that there were negligible benefits of neonicotinoid applications to crop yield (maize, in this particular study), at least given current application practices.

The results of the study performed by Krupke and colleagues show how the unintended consequences of pest management practices can ripple across the community. In this case, the consequences are particularly severe: neonicotinoids have harmful effects on honeybees, a key provider of pollination ecosystems services, with little benefit for the crops they are supposed to be protecting from pest insects. Despite these negative consequences, the work of the authors does suggest some straightforward solutions. They suggest reducing the amount of crop seed that is treated with neonicotinoid insecticides to better reflect actual pest pressure on crops—this change will hopefully limit the amount of neonicotinoids to which the non-target species like honeybees are exposed.

The full article, Planting of neonicotinoid-treated maize poses risks for honey bees and other non-target organisms over a wide area without consistent crop yield benefit is available in Journal of Applied Ecology.

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