Neonicotinoid Pesticides Linked to Dramatic Decline in Butterfly Numbers

Tuesday 24th November 2015

A new study has shown a strong relationship between the decline of common and widespread British butterflies and the increasing use of neonicotinoid pesticides on arable crops. 

The research, a collaboration between the University of Stirling, Biological Records Centre, Butterfly Conservation and the University of Sussex, examined 17 species of widespread butterflies over the last 30 years, the declines of 15 were correlated to the area of the UK subject to treatment with neonicotinoid pesticides.  The relationships with neonicotinoids were stronger than with time alone and although summer temperature and the number of butterflies in the previous year were positively related to butterfly populations, these factors were not related to levels of neonicotinoid usage; leading the authors to conclude that neonicotinoids “may explain the concurrent rapid decline in butterfly populations”. Species such as the Wall brown, Small skipper and Small tortoiseshell appear to have been particularly heavily impacted.

Research on the impact of neonicotinoids on bee populations have largely focussed on the neonicotinoids that get into the pollen and nectar of crops and nearby wildflowers.  However, butterflies may be more heavily impacted by the planting dust emitted when seeds treated with neonicotinoids are planted.  A study published earlier this year found that dust levels on plants near arable fields were high enough to cause sub-lethal effects in caterpillars of the Monarch butterfly.  Another study, also this year, found mobile dust with a high concentration of neonicotinoids on the surface of fields that had not recently been treated with neonicotinoids, suggesting that toxic dust is spread far and wide in the environment.  This would explain why neonicotinoids are affecting the national populations of butterflies despite most of them not living directly adjacent to arable fields.

“Clearly the use of neonicotinoid seed treatments has been an unmitigated ecological disaster.  It is such a shame that the Government continues to support their use when the time has clearly come to extend the ban on seed treatments to cover all crops, not just Oilseed rape.” remonstrated Matt Shardlow CEO of Buglife.