Researchers from Germany have collated and analysed data from amateur entomologists trapping for insects across protected nature areas in the last previous 27 years, and found an alarming level of decline.
The abundance of flying insects has declined by over three-quarters, and up to 82 per cent in midsummer.
“The fact that the number of flying insects is decreasing at such a high rate in such a large area is an alarming discovery,” says lead author Hans de Kroon from Radboud University.
The research was published in Plos One, and analysed the flying insects caught between 1989 and 2016.
The insects were collected in malaise traps at 63 nature reserves across Germany by members of the Krefeld Entomological Society.
The researchers found that the decline occurred irrespective of habitat type and landscape configuration, and was likely due to large-scale factors.
“The honest truth is that we don’t know the cause of this massive decline,” says Professor Dave Goulson from the University of Sussex, who contributed to the research.
“My best guess is that we’ve made the farmland surrounding these reserves inhospitable to insect life, but why this land is inhospitable is a combination of factors, including large scale monoculture and the use of pesticides.
In the UK, similar long-term studies from Butterfly Conservation have shown large declines in butterflies and moths.
The State of the UK’s Butterflies 2015 report found that between 1976-2014 there was a decline in 45 per cent in UK habitat specialists such as chalkhill blue and pearl-bordered fritillary, whilst there was a decline of UK wider countryside species of 25 per cent.
A 40-year study from Rothamsted, and discussed in The State of the Britain’s Larger Moths 2013 report, found a decrease of 28 per cent in macro moths caught in light traps.
The research showed a clear difference between the north and south (with the dividing line along the 4500 N grid line, roughly where York is). In southern Britain, including much of England and all of Wales, moth abundance decreased by 40 per cent.