Neonicotinoid insecticides are highly persistent and can contaminate freshwater and the nectar and pollen of crops and wildflowers. Their use is heavily restricted in the EU.
Two novel insecticides – sulfoxaflor and flupyradifurone – target insects in the same way as neonicotinoids, but are approved for use in the EU, Canada and the US. However, literature analysis reveals they have similar deleterious effects on beneficial insects (Proc. R. Soc. B, 2020, 287, 20201265).
‘What stands out is how similar their sub-lethal effects are to the neonicotinoids,’ says bee biologist Harry Siviter at the University of Texas at Austin, US, who led the literature review. ‘They can cause bees to have a lower reproductive output, which is obviously very important.’
Flupyradifurone and sulfoxaflor both kill pest species that are resistant to neonicotinoids, so they are likely to replace the older insecticides where there is resistance and also where neonicotinoids are banned or restricted.
Yet, the review points to studies indicating that flupyradifurone can increase risk of death in bumblebees at exposure levels typically found outside. Sulfoxaflor can kill bee larvae at field realistic concentrations when the young bees also have a common bee parasite.
Siviter and colleagues previously reported that spraying sulfoxaflor at realistic doses led colonies to produce fewer workers (Nature, 2018, 561, 109). The researchers cautioned against it directly replacing neonicotinoids.
‘They also bind to the acetylcholine receptors in the bee brain. They have the same mode of action as neonicotinoids, so it is hardly surprising that they have similar sublethal effects,’ says bee scientist Dave Goulson at the University of Sussex, UK. ‘The regulatory process to screen pesticides coming to market simply hasn’t changed since the neonicotinoids in the 1990s. There are no [additional] safety guards.’
Neonicotinoids came under scrutiny, not due to regulators, but owing to university research. Now, Siviter and others worry that the newer insecticides will simply follow the same path.
Shortcomings of the regulatory process are to blame, say its critics. ‘There are 20,000 species of bee. Yet regulators use the honeybee as a model species, which is a bit of an oddity and not representative of other bees,’ says Siviter. He suggests bumblebees or other wild bees should be included in regulatory studies.
Also, although fungicides and insecticides are studied and regulated as single compounds, they usually occur in agrochemical cocktails. These may interact and produce worse outcomes for bees and other beneficial insects, something regulators don’t take into account. As with approved human drugs, the impact of insecticides should be monitored after approval, for unanticipated negative ecological consequences, Siviter adds.
He sees little quantification of the benefits from insecticides. ‘We have documented skyrocketing levels of insecticide active ingredients in some of our largest cropping systems over the last 15 years or so,’ says Christian Krupke, an entomologist at Purdue University in Indiana, US. ‘It is convenient and allows farmers peace of mind in terms of controlling unseen pests,’ says Krupke, yet recent research suggests target pests are rarely even present (Journal of Economic Entomology, 2020, 113, 2197).