Scientists measure 76% plunge in flying insect numbers — in "nature preserves"

A June 8 Wall Street Journal feature by Jo McGinty reports that researchers documented a 76% drop during 1989-2016 in the number of flying insects living in 63 German nature preserves.

June 9, 2018 — Entomologists around the world are aware that insect numbers, and the range of species, has been declining for decades. But this is the first "hard" data that covers an entire nation's ecosystem — in supposedly protected nature preserves.

A wide variety of flying insects have vital roles in pollination. Typically a healthy ecosystem has many more beneficial species than problem insects like mosquitoes which bother humans.

You can browse the scientific summary and detailed data in the published scientific paper at this link

The 12 researchers say: "We show that this decline is apparent regardless of habitat type, while changes in weather, land use, and habitat characteristics cannot explain this overall decline."

The nature preserves are typically surrounded by farmland. We'd observe — as the scientists do — that one change which could be documented over the 27 years is a rapidly rising level of multiple agricultural chemicals applied on fields bordering the nature preserves. Flying insects don't hang out just in their home woods; they roam the surrounding countryside and return. The researchers used traps which caught only winged species. 

The authors saw no significant changes in climate for the studied region. A very slight observed average warming, they said, should have enhanced populations of flying bugs. Their discussion sums up, cautiously:

"Increased agricultural intensification may have aggravated this reduction in insect abundance in the protected areas over the last few decades. Whatever the causal factors responsible for the decline, they have a far more devastating effect on total insect biomass than has been appreciated previously.

"The widespread insect biomass decline is alarming, ever more so as all traps were placed in protected areas that are meant to preserve ecosystem functions and biodiversity."