The is worrisome because the study took place in protected areas, indicating the decline of flying insect populations in other areas, such as agricultural or urban areas, could be more prominent, Latty noted.
But the trend continued.
Over the past 27 years, they found an average decline of 76 percent, with the effects appearing worst in summer (82 percent). This way, many flying insects can be grouped in just one trap. "There is a huge paucity of data on historical patterns of insect populations and work on ecological phenomena that depend upon insects has long suffered due to this gap in our knowledge".
"As one of the few studies assessing overall biomass this study is a useful complement to the larger set of studies on specific groups of insects", writes John Losey, an entomologist at Cornell University in NY, in an email to The Scientist. "It is possible that these areas act as an "ecological trap" and jeopardize the populations in the nature reserves".
While it is well documented that butterflies and bees have been disappearing in Europe and North America, the study in PLOS ONE is the first to document that flying insects in general have decreased by more than three-quarters across Germany since 1989.
Christian Krupke, an entomologist at Purdue University, agrees.
"I think it's likely [that] it's how the surrounding land is being managed, because the nature reserves themselves haven't really changed, but the surrounding landscape is full of these big monoculture crops treated with lots of insecticides", says Goulson, a biology professor at the University of Sussex in Brighton, U.K.
While the study did not pinpoint a reason for the drop, researchers said many nature reserves are encircled by farm fields, and that pesticides could be to blame.
Insects play a crucial role in ecosystem functioning, pollinating 80 percent of wild plants and providing a food source for 60 percent of birds. "The research areas are mostly small and enclosed by agricultural areas".
"The remarkable and alarming aspect of this long-term study is the magnitude of the decline", notes Losey.
"But exactly what is causing their death is open to debate". "Most previous studies have reported biomass declines of less than 50 percent which is disconcerting".