Three-quarters of the total insect population lost in protected nature reserves

from Radboud University Nijmegen, October 18, 2017

Since 1989, in 63 nature reserves in Germany the total biomass of flying insects has decreased by more than 75%. This decrease has long been suspected but has turned out to be more severe than previously thought. Ecologists from Radboud University together with German and English colleagues published these findings in the scientific journal PLoS ONE on October 18th, 2017.

In recent years, it became clear that the numbers of many types of insects such as butterflies and bees were declining in Western Europe and North America. 'However, the fact that flying insects are decreasing at such a high rate in such a large area is an even more alarming discovery,' states project leader at the Radboud University Hans de Kroon.

Thorough research

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. The researchers from Nijmegen, Germany and England have now been able to analyse this treasure trove of data for the first time.

Decline also recorded in well-protected areas

The researchers discovered an average decline of 76 percent in the total insect mass. In the middle of summer, when insect numbers peak, the decline was even more severe at 82%. According to Caspar Hallmann from Radboud University who performed the statistical analyses, 'All these areas are protected and most of them are managed nature reserves. Yet, this dramatic decline has occurred.'

The exact causes of the decline are still unclear. Changes in the weather, landscape and plant variety in these areas are unable to explain this. The weather might explain many of the fluctuations within the season and between the years, but it doesn't explain the rapid downward trend.

A decline in other parts of the world too

Researchers can only speculate about the possible causes. 'The research areas are mostly small and enclosed by agricultural areas. These surrounding areas inflict 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,' explains Hallmann. It is likely that 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

'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,' states Hans de Kroon. 'We can barely imagine what would happen if this downward trend continues unabated.'

Because the causes of the decline are not yet known, it is difficult to take any concrete measures. The researchers hope that these findings will be seen as a wake-up call and prompt more research into the causes and support for long-term monitoring.

Measures

De Kroon: '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.'

https://www.eurekalert.org/pub_releases/2017-10/run-tot101717.php

Shocking > 75% decline in flying insects in last 27 years

Since 1989, numbers of flying insects have dropped by more than 75% in parts of Germany, with serious implications for the rest of Europe.

by Tim Radford, Climate News Network, October 20, 2017

LONDON – The mass of flying insects in parts of Germany has fallen by three-quarters in the last 27 years. Since the territories sampled were all nature reserves in some way protected from pesticides and other disturbance, the implications are alarming: winged insects may be flying to oblivion across much of Europe.

The cost to natural ecosystems and to human economies could be devastating. Insects pollinate 80% of wild plants, feed on species that could otherwise become pests, recycle plant and animal waste, and are themselves food for 60% of birds. One calculation places the value of wild insect pollination at $57bn a year in the United States.

Vanishing insects

Researchers have already expressed concern about the vanishing numbers of butterflies in parts of Europe, possibly as a consequence of climate change. But the latest study does not distinguish individual species or even groups. It concentrates just on the sheer mass of flying insects in a German growing season.

The research – published in the Public Library of Science journal, PLOS ONE – assembles 1,503 records of winged insects, all caught in a standard field trap, in 63 unique locations in protected areas in lowland Germany during spring, summer and early autumn from 1989 to 2016. The data told a disconcerting story: the average seasonal mass of flying insects declined by 76% in under three decades. At the height of summer, the decline reached 82%.

“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”

The decline was consistent regardless of the type of habitat – dunes, heath land, rich and poor grasslands, wastelands, shrub cover and so on – and changes of land use or weather, or shifts in the habitat itself offered no obvious explanation. Researchers have identified reasons that one species, or a group of insects, might be at risk from climate change, perhaps because earlier flowering disrupts the feeding cycle or because the mix of species in an ecosystem changes with rising temperatures.

But there has always been an unspoken assumption that other species or groups of species may be likely to benefit from the change, by extending their range. The study is based on observations made only in one country. However, the finding implies that ecosystems across the whole of Europe could be affected, on a huge scale and at every level.

Downward trend

“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,” says Hans de Kroon, an ecologist at Radboud University in Nijmegen in the Netherlands, one of the authors.

“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.”