The loss of bees, butterflies and other flying insects has been more severe than previously feared, new research reveals. The total biomass of flying insects in German nature reserves has decreased by more than 75% over the past 27 years, according to a study published in the journal PLOS ONE on October 18th. The gradual decline of certain insect species has been known for some time. “However, the fact that flying insects are decreasing at such a high rate in such a large area is an even more alarming discovery,” said Hans de Kroon, project leader at Radboud University in Nijmegen. One cause for this decline could be agricultural intensification in the areas close to the reserves. “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,” said co-author Prof Dave Goulson. “On current trajectory, our grandchildren will inherit a profoundly impoverished world,” he warns.

For the study, insect researchers in Germany collected data between 1989 and 2016 in 63 different places within nature reserves, embedded in a landscape dominated by agriculture. Flying insects were trapped in so-called malaise traps throughout the season (March through October) and the total biomass was then weighed and compared. Researchers from Nijmegen, Germany and England then analysed the extensive data set. They found that the total insect mass declined by an average of 76% between 1989 and 2016. In the middle of summer, when insect numbers peak, the decline was even more pronounced at 82%. “All these areas are protected and most of them are managed nature reserves. Yet, this dramatic decline has occurred,” said Caspar Hallmann from Radboud University who conducted the statistical analyses. The scientists admit that the exact causes of the decline are still unclear and cannot be attributed to changes in the weather, landscape and plant variety alone. “Part of the explanation could therefore be that the protected areas (serving as insect sources) are affected and drained by the agricultural fields in the broader surroundings,” they suspect. According to the authors, increased agricultural intensification may have aggravated this reduction in insect abundance in the protected areas. “The research areas are mostly small and enclosed by agricultural areas,” Hallmann added. “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.”

The researchers hope that their findings will serve a wake-up call and prompt more research into the causes and support for long-term monitoring. “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,” said Hans de Kroon. “We can barely imagine what would happen if this downward trend continues unabated.” For example, 80% of wild plants are estimated to depend on insects for pollination, while 60% of birds rely on insects as a food source. The ecosystem services provided by wild insects have been estimated at $57 billion annually in the US. “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," de Kroon said. “But we also have to work hard at extending our nature reserves and decreasing the ratio of reserves that border agricultural areas.” (ab)