No Simple Answers for Insect Conservation: Media hype has missed the biggest concern that ecologists and entomologists have about six-legged life: how little we know about it
In late 2017, ecologist Caspar Hallmann of Radboud University in the Netherlands and his colleagues published an analysis of data from the Entomological Society Krefeld in Germany that showed a decline of more than 70 percent in flying insect biomass (the volume of living matter) over a 27-year period. A year later, ecologists Bradford Lister of the Rensselaer Polytechnic Institute and Andres Garcia of the Universidad Nacional Autonoma de Mexico published a study from the Luquillo Experimental Forest in Puerto Rico suggesting a long-term decline in arthropod biomass and a restructuring of the area's food web because of increased local temperatures. Earlier this year, Francisco Sanchez-Bayo of the University of Sydney and Kris Wyckhuys of the University of Queensland published a review paper provocatively titled "Worldwide Decline of the Entomofauna."
As each study came out, the surrounding hype grew, filling broadcast and online platforms for popular-science news with a heady mix of hyperbole, anecdote, and speculation, including such dire phrases as "insect apocalypse," "global ecosystem collapse," "loss of all insects within 100 years," and "collapse of entire food webs." But these stories also claimed that our most hated pests, such as cockroaches and houseflies, would be the exceptions, set to boom out of control as all other insects disappeared.
Widespread, consistent insect declines are a real concern. Yet there is little published evidence that worldwide decline of all insects is happening. The aforementioned studies were localized and skewed toward particular taxa. The authors of the Krefeld and Luquillo studies tried not to overextend their results in their journal articles, but the press releases from the lead authors' institutions, media coverage, and the recent review paper were less cautious. Sanchez-Bayo and Wyckhuys claimed that their review showed that "almost half of the [world's insect] species are rapidly declining." Yet their data show declines for only about 2,900 species--a tiny fraction of the estimated 5 million insect species on Earth.
Ecological patterns observed in one location are affected by complex interactions between local animal communities, regional attributes, human activities, and the study methods used, among other factors. This essential context is often considered too complicated to include in sound-bite stories. But when we overlook this complexity, we are ignoring the very information we need to take action to save threatened insect populations.
The Krefeld study is based on trap samples from 63 nature reserve sites in Germany, collected over a 27-year period. But more than half the sites were only surveyed once during the study period, and only 26 sites were surveyed in multiple, though not consecutive, years. The lack of repeated sampling at exactly the same locations over a long period of time limits understanding of the true extent of declines across Europe, let alone in the rest of the world. Moreover, biomass is a poor proxy for abundance or species richness.
Similarly, the Luquillo Forest study compared arthropod biomass from two sampling occasions in the 1970s with data from the same site collected in 2011 and 2012. Without knowing what...