More than 40% of insect species could become extinct over the next few decades, leading to a “catastrophic collapse of nature’s ecosystems”, a new study has warned. According to the first global scientific review, published in the journal Biological Conservation, insects could even vanish within a century at the current rate of decline. The authors made a review of 73 historical reports of insect declines from across the world and systematically assessed the reasons behind the decline. They found that insect decline is not just a local phenomenon; the biodiversity of insects is threatened worldwide. “Our work reveals dramatic rates of decline that may lead to the extinction of 40% of the world’s insect species over the next few decades,” they wrote in the abstract of the study. The rate of extinction is eight times faster than that of mammals, birds and reptiles. Insect biomass is declining by a staggering 2.5% a year, the review found. The 2.5% rate of annual loss over the last 25-30 years is “shocking”, one of the authors, Francisco Sánchez-Bayo from the University of Sydney, told the Guardian. “It is very rapid. In 10 years you will have a quarter less, in 50 years only half left and in 100 years you will have none.”

In terrestrial ecosystems, the taxa most affected were butterflies, Hymenoptera (the order comprising insects with membranous wings such as the wasps, bees, and ants) and dung beetles (Coleoptera). In addition, four major aquatic taxa (Odonata, Plecoptera, Trichoptera and Ephemeroptera) have already lost a large proportion of species. The authors write that affected insect groups not only include specialists that occupy particular ecological niches, but also many common and generalist species. But there is also a small number of species whose abundance is increasing. “These are all adaptable, generalist species that are occupying the vacant niches left by the ones declining. Among aquatic insects, habitat and dietary generalists, and pollutant-tolerant species are replacing the large biodiversity losses experienced in waters within agricultural and urban settings,” the abstract reads.

The study warns that habitat loss and conversion to intensive agriculture and urbanization is the main driver of the declines. They blame pollution, mainly that by synthetic pesticides and fertilisers. “Unless we change our ways of producing food, insects as a whole will go down the path of extinction in a few decades,” the authors were cited by the Guardian. “The repercussions this will have for the planet’s ecosystems are catastrophic to say the least.” Additional causes are biological factors, including pathogens and introduced species, as well as climate change. Climate change is particularly important in tropical regions, but only affects a minority of species in colder climes and mountain settings of temperate zones.

“If insect species losses cannot be halted, this will have catastrophic consequences for both the planet’s ecosystems and for the survival of mankind,” Sánchez-Bayo told the Guardian. The decline in insect populations will especially affect the birds, reptiles, amphibians and fish that eat insects. “If this food source is taken away, all these animals starve to death,” he added. In order to stop the decline, decisive action is needed. According to the authors, “a rethinking of current agricultural practices, in particular a serious reduction in pesticide usage and its substitution with more sustainable, ecologically-based practices, is urgently needed to slow or reverse current trends, allow the recovery of declining insect populations and safeguard the vital ecosystem services they provide.” In addition, effective remediation technologies should be applied to clean polluted waters in both agricultural and urban environments.” (ab)