Neonicotinoids ‘may damage butterfly populations’

Neonicotinoid pesticides may be linked to declining butterfly populations, scientists have warned.

Findings from the first scientific study to suggest that neonicotinoid pesticides may have a negative effect on UK butterfly populations were published on Tuesday (24 November).

The study was conducted by the Universities of Stirling and Sussex in partnership with Butterfly Conservation and the Centre for Ecology and Hydrology.

See also: Neonicotinoid ban ‘may be permanent’

The study found population trends of 15 butterfly species showed declines associated with neonicotinoid use – including the small tortoiseshell (pictured), small skipper and wall species.

Findings were based on data gathered by volunteers from more than 1,000 sites across the UK as part of the long-running UK Butterfly Monitoring Scheme (UKBMS).

Researcher Andre Gilburn, who led the study, said the study suggested the strength of the effect neonicotinoids may be having on many species “could be huge”.

Findings from the study, Are neonicotinoid insecticides driving declines of widespread butterflies?, were published in the journal PeerJ.

In England, the overall population level of widespread butterflies on monitored farmland sites declined by 58% between 2000 and 2009, the report says.

This decline had occurred despite conservation spending in the UK more than doubling in real terms over the same period, it adds.

Habitat deterioration resulting from land-use change was likely to be the most important factor driving long-term declines of UK butterflies.

Weather was likely to be the principal factor determining inter-annual fluctuations in butterfly numbers. But the precise reasons for recent declines are undetermined.

“Of the factors we tested, three correlated significantly with butterfly populations,” says the report summary.

“Summer temperature and the index for a species the previous year are both positively associated with butterfly indices.

“By contrast, the number of hectares of farmland where neonicotinoid pesticides are used is negatively associated with butterfly indices.”

Indices for 15 of the 17 species showed negative associations with neonicotinoid use.

“The declines in butterflies have largely occurred in England, where neonicotinoid use is at its highest. In Scotland, where neonicotinoid use is comparatively low, butterfly numbers are stable.”

Tom Brereton, head of monitoring at Butterfly Conservation, said urgent research was needed to see whether the correlations were caused by neonicotinoids or another aspect of intensive farming.

“Widespread butterflies have declined by 58% on farmland in England over the past 10 years, giving concern for the general health of the countryside and for these and other insects in particular.”