Two separate studies from the United States and England, both published today, show evidence that populations of butterflies and wild bees have declined in association with increased neonicotinoid use.
Neonicotinoids, or neonics, are pesticides applied to crops as seed treatments or sprays. Neonics have high selective toxicity for insects, meaning they are more toxic to insects than mammals. When insects eat the treated plants, the pesticides affect the insects' health, behaviour and reproductive success.
While there have been few studies in the natural environment until now, concerns about the ecological impact of neonics, including their possible link to bee declines, led the European Union to restrict their use in 2013. EU scientists are currently reviewing the ban, with recommendations expected next year.
What Do The New Studies Tell Us?
In the US study, researchers looked at 40 years of butterfly data in northern California. They found that populations declined dramatically in the late 1990s. Smaller butterfly species that produced fewer generations each year were the most affected.
These declines were associated with increasing use of neonics across the region, beginning in the mid-1990s. The data for neonics usage was obtained from US government pesticide use databases.
This study is an important contribution to our understanding of how neonics affect non-target insects in the wild.
The butterfly data was collected from four sites monitored by the same person (an expert entomologist) for up to four decades. This level of data integrity is quite rare in modern ecological studies. Long-term consistency in the data collection means that many of the effects of different observer skills or collection efforts have been minimised.
Honey bee. David Peter Ryan/Shutterstock
The second study looked at wild bee populations in the UK. The researchers focused on oilseed rape that had been seed-treated with the pesticide. Rape is a common source of neonics in agricultural environments and is also a highly attractive floral resource for many wild bees and other pollinator insects.
This study also uses high-quality data. It is based on 18 years of data for 62 bee species collected by the Bees, Wasps and Ants Recording Society, a specialist UK entomological society, as well as pesticide use data from the UK government. The researchers show that, over time, the negative effects of neonics exposure for wild bees outweighed the benefits of the crop as a food resource.
They provide the first evidence that neonic seed treatments are associated with national-scale declines in wild bees at the community level. Populations of species that are known to forage regularly on rape were affected three times more than species not seen on rape flowers.