Study on Insect Decline Highlights Need for Enhanced Research and Conservation

malaise trap in German field

A 27-year study in western Germany, using malaise traps placed in protected habitats such as shown above, measured total biomass  of flying insects and found a decline of more than 75 percent in that time period. Researchers suggest large-scale trends could be driving the decline and note the need for similar study to measure insect levels worldwide. (Photo originally published in Halmann et al., PLOS ONE, October 2017)

No doubt you saw the headlines last week:

A study published in PLOS ONE reports a decline of more than 75 percent in insect biomass over a 27-year period in western Germany. Researchers with the Entomological Society Krefeld used malaise traps in varying locations in protected habitats to measure total biomass of flying insects caught, between 1989 and 2016. The overall trend: a 76.7 decline over that period, and no one “silver bullet” explanation appeared to be the cause. “The decline in insect biomass, being evident throughout the growing season, and irrespective of habitat type or landscape configuration, suggests large-scale factors must be involved,” say the researchers.

It’s a dramatic finding, and a concerning one if it is representative of global trends.

Helen Spafford, Ph.D., associate professor in the Department of Plant and Environmental Protection Sciences at the University of Hawaii, Manoa, cautions against extrapolating the findings of the German study broadly to other locations but says she finds it worrisome, nonetheless.

“The study warrants concern for other places around the world, particularly where threatened or endangered species are located,” Spafford says. “There are few studies that do this, and I urge any other groups who have been collecting like this to share their data. That way we can see if the declines in Germany are occurring elsewhere.”

If there’s reason to think similar declines are happening across the globe, it’s because the large-scale trends that contributed to the findings in Germany aren’t exclusive to that region, says Jason R. Cryan, Ph.D., deputy director and chief of research and collections at the North Carolina Museum of Natural Sciences.

“Although no specific cause of that decrease is identified, several factors are likely important contributors, including climate change, habitat fragmentation and destruction, and the increased usage of pesticides and other chemicals in agricultural, urban, and semi-urban environments,” Cryan says. “Although the study was conducted entirely in Germany, these contributory factors are common globally, and thus we can expect that insect population declines of similar magnitude are occurring in other regions of the world.”

In 2017, the Entomological Society of America issued formal position statements on endangered insect species and arthropod biodiversity. (Spafford participated on the volunteer writing committee for the former, Cryan on the latter.) Both statements cite the critical role insects play in healthy ecosystems and note that insects can often be early indicators of ecological shifts, and they call for enhanced research and conservation. The findings from the long-term study in Germany underscore that need.

“This study has sounded the alarm for entomologists and others,” says Spafford. “We can’t just turn it off or switch it back to snooze. We need to wake up. If we are seeing these kinds of declines in insect biomass, then undoubtedly other organisms that are connected to these insect populations will be affected also. The cascading effects could be significant for plants, other animals, nutrient and decomposition cycles, and increase the vulnerability of systems to invasive species.”

Cryan concurs: “Insects are responsible for critical environmental services … upon which the Earth’s environment—and, more pointedly, human activities—depend. Removal of those pieces of the natural puzzle can only be detrimental to the entire system.”

Comments

  1. One scenario they don’t consider is that intensified agriculture has greatly reduced the numbers of highly agile pests like leafhoppers, aphids and, especially, cutworms, armyworms, etc. These ” junk” species often make up large parts of light trap and malaise trap catches even in areas quite remote from farms. Whereas they suggest farms are a sink for insects coming out of their natural habitats, I think they need to consider that they may be a source, which more intense use of pesticides in agriculture is cutting off.

  2. Paul Cherubini says:

    What “critical environmental services … upon which human activities—depend” are threatened in Europe on account of the decrease in insect biomass? Industry and the general public want to know. Can’t be pollination services because honeybee populations and food crop yields in Europe are rising.

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