Worldwide decline of the entomofauna: A review of its drivers

Abstract

Journal of Biological Conservation: Biodiversity of insects is threatened worldwide. Here, we present a comprehensive review of 73 historical reports of insect declines from across the globe, and systematically assess the underlying drivers. 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. In terrestrial ecosystems, Lepidoptera, Hymenoptera and dung beetles (Coleoptera) appear to be the taxa most affected, whereas four major aquatic taxa (Odonata, Plecoptera, Trichoptera and Ephemeroptera) have already lost a considerable proportion of species. Affected insect groups not only include specialists that occupy particular ecological niches, but also many common and generalist species. Concurrently, the abundance of a small number of species 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 main drivers of species declines appear to be in order of importance: i) habitat loss and conversion to intensive agriculture and urbanisation; ii) pollution, mainly that by synthetic pesticides and fertilisers; iii) biological factors, including pathogens and introduced species; and iv) climate change. The latter factor is particularly important in tropical regions, but only affects a minority of species in colder climes and mountain settings of temperate zones. 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. Click here to read the article

Plummeting insect numbers ‘threaten collapse of nature’

Guardian Exclusive: ‘Insects could vanish within a century at current rate of decline, says global review

The world’s insects are hurtling down the path to extinction, threatening a “catastrophic collapse of nature’s ecosystems”, according to the first global scientific review.

More than 40% of insect species are declining and a third are endangered, the analysis found. The rate of extinction is eight times faster than that of mammals, birds and reptiles. The total mass of insects is falling by a precipitous 2.5% a year, according to the best data available, suggesting they could vanish within a century.

The planet is at the start of a sixth mass extinction in its history, with huge losses already reported in larger animals that are easier to study. But insects are by far the most varied and abundant animals, outweighing humanity by 17 times. They are “essential” for the proper functioning of all ecosystems, the researchers say, as food for other creatures, pollinators and recyclers of nutrients.

Insect population collapses have recently been reported in Germany and Puerto Rico, but the review strongly indicates the crisis is global. The researchers set out their conclusions in unusually forceful terms for a peer-reviewed scientific paper: “The [insect] trends confirm that the sixth major extinction event is profoundly impacting [on] life forms on our planet.

“Unless we change our ways of producing food, insects as a whole will go down the path of extinction in a few decades,” they write. “The repercussions this will have for the planet’s ecosystems are catastrophic to say the least.”

The analysis, published in the journal Biological Conservation, says intensive agriculture is the main driver of the declines, particularly the heavy use of pesticides. Urbanisation and climate change are also significant factors.

“If insect species losses cannot be halted, this will have catastrophic consequences for both the planet’s ecosystems and for the survival of mankind,” said Francisco Sánchez-Bayo, at the University of Sydney, Australia, who wrote the review with Kris Wyckhuys at the China Academy of Agricultural Sciences in Beijing.

The 2.5% rate of annual loss over the last 25-30 years is “shocking”, Sánchez-Bayo 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.” One of the biggest impacts of insect loss is on the many birds, reptiles, amphibians and fish that eat insects. “If this food source is taken away, all these animals starve to death,” he said. Such cascading effects have already been seen in Puerto Rico, where a recent study revealed a 98% fall in ground insects over 35 years.

The new analysis selected the 73 best studies done to date to assess the insect decline. Butterflies and moths are among the worst hit. For example, the number of widespread butterfly species fell by 58% on farmed land in England between 2000 and 2009. The UK has suffered the biggest recorded insect falls overall, though that is probably a result of being more intensely studied than most places.

Bees have also been seriously affected, with only half of the bumblebee species found in Oklahoma in the US in 1949 being present in 2013. The number of honeybee colonies in the US was 6 million in 1947, but 3.5 million have been lost since.

There are more than 350,000 species of beetle and many are thought to have declined, especially dung beetles. But there are also big gaps in knowledge, with very little known about many flies, ants, aphids, shield bugs and crickets. Experts say there is no reason to think they are faring any better than the studied species. A small number of adaptable species are increasing in number, but not nearly enough to outweigh the big losses. “There are always some species that take advantage of vacuum left by the extinction of other species,” said Sanchez-Bayo. In the US, the common eastern bumblebee is increasing due to its tolerance of pesticides.’