The recently published article “Worldwide decline of the entomofauna: A review of its drivers”, by Francisco Sánchez-Bayo from the Sydney Institute of Agriculture in the School of Life and Environmental Sciences (University of Sydney), and Kris A.G. Wyckhuys (University of Queensland and the Institute of Plant Protection, China Academy of Agricultural Sciences) has received abundant popular news media coverage and it has created justified anxiety among the public.
I think it is always a good idea to refer readers to the source. So, these are the highlights of the paper and its abstract, verbatim:
Highlights
- Over 40% of insect species are threatened with extinction.
- Lepidoptera, Hymenoptera and dung beetles (Coleoptera) are the taxa most affected.
- Four aquatic taxa are imperiled and have already lost a large proportion of species.
- Habitat loss by conversion to intensive agriculture is the main driver of the declines.
- Agro-chemical pollutants, invasive species and climate change are additional causes.
Abstract
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.
The paper can be found here, but is paywalled. It costs $35.95 (although other publications often make special articles like that freely available in the public interest, regrettably Elsevier decided to charge for it; likewise, although researchers often make available free pre-print versions of their papers, it seems there is no such version of this paper).
Anyway, a review paper is meant to do that: it reviews a number of articles on a subject, collates and summarises their findings. That’s what the Sánchez-Bayo/Wyckhuys paper does with 73 pre-existing articles.
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A digression is necessary at this point. That some insect species had been declining and that this may have different causes are not new findings. It has been known for a while that honey bee and bumble bee populations, for example, had been not only decreasing but going locally extinct in some parts of Europe and North America. The suspected causes of those declines are many: pesticides, monoculture, disease, climate change, for example.
The finding that those declines were widespread and not limited to a few insect species, however, is much more recent. The path-breaking article was published in October 2017: “More than 75 percent decline over 27 years in total flying insect biomass in protected areas”, by Caspar A. Hallmann and 11 co-authors.
The unusual history of that discovery is fascinating in itself, definitely well-worth your time. Gretchen Vogel tells it here. Suffice it to say it was largely fortuitous and made possible only because over decades some very enterprising and dedicated German amateur naturalists from the city of Krefeld at their own expenses collected the data, consistently using the same methods, even before they had a clear idea of what to do with that. Eventually they were discovered by some very lucky and open-minded Dutch, German and British professional researchers. That’s how that paper was born.
Researchers aren’t usually that lucky. Science in general has neglected collecting the kind of data those amateur naturalists keenly collected. There are many reasons for that. A partial explanation will have to wait for the near future. At any rate, here it’s enough to say that entomology is not a sexy area of research and most research on insects focuses on commercially important species (like bees, which in 2017 deserved consideration even in parliamentary halls) and on eliminating pests.
The bottom line is that researchers into the decline of insect populations either work with treasure troves of data like that where and if they find them, or must come up, on a case-by-case basis, with indirect evidence (Vogel mentions an example for a Canadian case: sifting through deposits of chimney swifts droppings in an attempt to reconstruct the bird’s insect diet).
Admittedly, that isn’t an ideal situation and is not conducive to produce a more complete geographical coverage to document insect population decline globally. But that’s the situation we have and the data available. With that data Sánchez-Bayo and Wyckhuys managed to get a global picture, however tentative. They also managed to eliminate disease as a general explanation. And they did that in short notice: about a year and half after the Krefeld paper.
Short of going back in time to start collecting that data, there’s no easy way around: there’s no Krefeld Entomological Society in the Amazonian rainforest, nor many chimneys, abandoned or not, in the Kimberley.
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The point of that digression is that it has been observed that scientists dealing with catastrophic environmental events often adopt an overly cautious stance. Sometimes this manifests itself as demanding standards of evidence which, while in more propitious circumstances would be ideal, in the current reality are unreasonable.
This excessively cautious stance has been noticed in the specific case of climate change and is cause of serious concern. Its symptom there is extremely optimistic predictions, like those the IPCC formulate about climate change. They often fall well short of reality: oceanic warming and acidification, carbon emissions growth, average temperatures increase, Arctic meltdown, sea-level rise, are all proceeding considerably faster than predicted. And yet, conservative predictions continue to be formulated.
One of the reasons advanced to explain that systematic underprediction is the desire to avoid “alarmism”.
Now ABC News, ABC The World Today, and NewScientist report similar reactions to the Sánchez-Bayo/Wyckhuys paper. The suggestion that one must wait until more research is carried out in places less covered by data -- like Africa, Asia and Australia -- is not only hard to qualify, but is probably destined to fail: there is no reason to believe reliable studies will be carried out if no data exist.
That kind of reaction is not only troublesome, but probably entirely unjustified, as the chart below suggests. In a country like Australia, where in a hellish summer we’ve seen temperature records broken everywhere, followed by an unseasonal snow fall in Tasmania, mass animal deaths, unprecedented bushfires which in Tasmania alone reduced 3% of its area to ashes and once-in-a-century floods in Queensland, the Banking Royal Commission and Brexit (yes, believe it or not) compete for the public’s attention.
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| Screen capture taken on 13/02/2019. |
I suspect scientists have little reason to fear widespread panic. And I suggest right now some level of alarm would be a healthy reaction.
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Francisco Sánchez-Bayo comments.
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