Professor Dave Goulson

The loss of bees, butterflies and other flying insects from within protected nature reserves has been even more severe than previously feared, a new report has revealed.

The total biomass of flying insects in 63 nature reserves has decreased by more than 75 per cent since 1989 and above 80 per cent in the height of summer.

Researchers believe insect populations are becoming trapped on nature reserves surrounded by inhospitable farmland.

Ecologists from Radboud University, who worked together with German and English colleagues including Professor Dave Goulson at the University of Sussex, said the rate of loss was not sustainable.

Hans de Kroon, project leader at the Radboud University in Nijmegen in The Netherlands, said: “The fact that flying insects are decreasing at such a high rate in such a large area is an alarming discovery.”

Co-author Prof Dave Goulson said: “Insects make up about two thirds of all life on Earth.
“We appear to be making vast tracts of land inhospitable to most forms of life, and are currently on course for ecological Armageddon.
“On current trajectory, our grandchildren will inherit a profoundly impoverished world.”

Decline also recorded in well-protected areas

Entomologists (insect researchers) in Krefeld, Germany, led by Martin Sorg and Heinz Schwan, collected data over the past 27 years in 63 different places within nature reserves across Germany.

Flying insects were trapped in malaise traps and the total biomass was then weighed and compared. Researchers from Nijmegen, Germany and England have now been able to analyse the extensive data set for the first time.

The researchers discovered an average decline of 76 percent in the total insect mass while in the middle of summer, when insect numbers peak, the decline was even more severe at 82 percent. 

Caspar Hallmann, from the Radboud University who performed the statistical analyses, said: “All these areas are protected and most of them are managed nature reserves. Yet, this dramatic decline has occurred.”

A decline in other parts of the world too

The exact causes of the decline are still unclear with changes in the weather, landscape and plant variety not sufficient to explain the rapid downward trend.

Caspar Hallmann said: “The research areas are mostly small and enclosed by agricultural areas.
“These surrounding areas attract flying insects and they cannot survive there.
“It is possible that these areas act as an ‘ecological trap’ and jeopardize the populations in the nature reserves.”

Investigators believe the results are representative for large parts of Europe and other parts of the world where nature reserves are enclosed by a mostly intensively used agricultural landscape.

Wake-up call

Researchers said it was difficult to take any concrete measures to tackle the decline when its causes remained unknown but hope that the findings will be seen as a wake-up call and prompt more research into the causes and support for long-term monitoring.

Hans de Kroon said: “As entire ecosystems are dependent on insects for food and as pollinators, it places the decline of insect eating birds and mammals in a new context.
“We can barely imagine what would happen if this downward trend continues unabated.
“The only thing we can do right now is to maintain the utmost caution. We need to do less of the things that we know have a negative impact, such as the use of pesticides and prevent the disappearance of farmland borders full of flowers.
“But we also have to work hard at extending our nature reserves and decreasing the ratio of reserves that border agricultural areas.”

The findings will be published in the scientific journal PLoS ONE tomorrow [Wednesday October 18].