Insect declines

So much has been written about the ‘insect apocalypse’; so many books, papers and articles are appearing all the time, that it can be difficult to make sense of it all. Unfortunately, and although there are a lot of ‘ifs’ and ‘buts’ and caveats, things do look rather alarming, particularly when we take a global perspective. Rather than trying to summarise the vast literature, I thought it would be useful to highlight a few recent reports from around the world that have caught my attention. I have also littered the text with my own photographs to remind ourselves what incredible organisms we are talking about!

The giant honey bee (Apis dorsata) workers, Thailand. Photo by Raymond JC Cannon

I don’t like to be a doom and gloom merchant, but where there is a real problem, we all need to become aware of it and try to fix it. And since at least 87 of major food crops, or ~85% of all cultivated crops (accounting for 35% of the world food production) depend on insect pollination (van der Sluijs, 2020), we need to get going. And it’s not just honey bees; wild bees are declining worldwide (Zattara & Aizen, 2019). As these authors say: the “Bees cannot wait“!

I think we humans have a sort of built-in, default position which assumes that things will be OK; that nature, or the planet, or Gaia, or God, will somehow take care of things and sort out the mess we have made. This at least explains why so many people reject the evidence of climate change. In the long run, in the very long run (say 50 to 100 million years) this may indeed happen. New species will evolve and diversity will increase again. But these geological time scales are of no relevance to us humans and the problems we face now.

Idea species from Malaysia. Photo by Raymond JC Cannon

Daniel H. Janzen is a distinguished biologist who has been working in Costa Rica since 1953. When he says there is a problem (Janzenm & Hallwachs, 2021), we really need to pay attention! These scientists have been monitoring and observing insects in the Guanacaste Conservation Area of NW Costa Rica or decades. What they are reporting is that ‘insect species richness and density have gradually declined since the late 1970s, and more intensely since about 2005’. According to these authors, the main reason for this perturbation is climate change. Alarmingly, they state that:

the biomass and species richness of insect individuals and species, and their interactions with everything, are decomposing“.

Guanacaste reserve, Coata Rica. Tizianok, CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons

Janzen & Hallwachs (2021) have lots of suggestions and concrete examples of how to turn things around. These include involving local and national stakeholders to “be be kind to the [insect] survivors” through education, building bioliteracy – ‘learning the language of nature’, as this blog describes it – so that everyone values what they have left. Barcoding is the way to make bioliteracy easier and more accessible, according to Janzen.

Cloudless Sulphur (Phoebis sennae) and White-angled sulphur (Anteos clorinde) and Large orange sulphur (Phoebis agarithe) butterflies from Argentina. Photo by Raymond JC Cannon

These sentiments about education and valuing wildlife apply equally to ourselves in Europe, as they do to people in the tropics. Perhaps more so, as we have a long history of destruction and de-wilding (albeit we are starting to think about re-wilding!). The Big Butterfly Count for 2020 saw the lowest numbers of butterflies recorded in 11 years; and the downward trend continued this year (2021). On average, butterfly numbers in the UK have declined by about 50% since 1976 (Warren et al., 2021), the year I graduated! The take-home-message seems to be that scarce, and/or specialized butterflies ‘have largely disappeared’ (Thomas, 2016), leaving ecosystems dominated by common generalist ones. This trend towards generalist species is seen elsewhere in Europe (Habel et al. 2019).

Small pearl-bordered fritillary (Boloria selene) female. Photo by Raymond JC Cannon

Butterflies are declining across large parts of Europe; the main reasons for this decline are thought to be habitat loss and degradation, and chemical pollution. Personally, I am more inclined to point the finger at habitat loss and land degradation, but as Prof Dave Goulson points out in this report on Insect declines and why they matter, every year, farmers make more pesticide applications to their crops, to provide us with the food we sometimes take for granted. This trend is even more apparent on a worldwide basis. China is the major user, followed by the USA and Argentina; in 2020, the global pesticide usage was estimated to be 3.5 million tonnes (Sharma et al., 2019).

The angleshades moth (Phlogophora meticulosa). Large moths doing better? Photo by Raymond JC Cannon

But, like I said, there are caveats, and it’s not all doom and gloom. Some species are becoming more common! Long-term datasets of macro-moths in Great Britain (The Rothamsted Insect Survey) have revealed that “Some species are not only persisting in the face of unprecedented anthropogenic pressure but appear to be thriving” (Boyes et al., 2019). The drivers (causes) of these changes are uncertain, but this study concludes that

“the increasingly widespread view that insect biomass is collapsing finds little support in what is perhaps the best insect population database available anywhere in the world.” (MacGregor et al., 2019).

So the reality is that although we know about some types of insects in certain areas of the world, where they are well-studied, our ‘knowledge of insect declines is still incomplete and scattered’ (Montgomery et al., 2020).

I will continue this theme, looking at some other examples from around the world, in another blog.😊

References

Boyes, D. H., Fox, R., Shortall, C. R., & Whittaker, R. J. (2019). Bucking the trend: the diversity of Anthropocene ‘winners’ among British moths. Frontiers of Biogeography11(3).

Goulson, D. (2019). The insect apocalypse, and why it matters. Current Biology29(19), R967-R971.

Habel, J. C., Trusch, R., Schmitt, T., Ochse, M., & Ulrich, W. (2019). Long-term large-scale decline in relative abundances of butterfly and burnet moth species across south-western Germany. Scientific reports9(1), 1-9.

Janzen, D. H., & Hallwachs, W. (2021). To us insectometers, it is clear that insect decline in our Costa Rican tropics is real, so let’s be kind to the survivors. Proceedings of the National Academy of Sciences118(2).

MacGregor, C. J., Williams, J., Bell, J., & Thomas, C. (2019). Moth biomass increases and decreases over 50 years in Britain. Nature Ecology and Evolution, 1-16.McDermott, A. (2021). News Feature: To understand the plight of insects, entomologists look to the past. Proceedings of the National Academy of Sciences118(2).

Montgomery, G. A., Dunn, R. R., Fox, R., Jongejans, E., Leather, S. R., Saunders, M. E., … & Wagner, D. L. (2020). Is the insect apocalypse upon us? How to find out. Biological Conservation241, 108327.

Murphy, S. M., Richards, L. A., & Wimp, G. M. (2020). Arthropod interactions and responses to disturbance in a changing world. Frontiers in Ecology and Evolution8, 93.

Thomas, J. A. (2016). Butterfly communities under threat. Science353(6296), 216-218.

Thomas, C., Jones, T. H., & Hartley, S. E. (2019). “Insectageddon”: A call for more robust data and rigorous analyses. Global change biology.

van der Sluijs, J. P. (2020). Insect decline, an emerging global environmental risk. Current Opinion in Environmental Sustainability.

Warren, M. S., Maes, D., van Swaay, C. A., Goffart, P., Van Dyck, H., Bourn, N. A., … & Ellis, S. (2021). The decline of butterflies in Europe: Problems, significance, and possible solutions. Proceedings of the National Academy of Sciences118(2).

Zattara, E. E., & Aizen, M. A. (2019). Worldwide occurrence records reflect a global decline in bee species richness. Available at SSRN 3669390.

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