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Decline in insect populations

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An annual decline of 5.2% in flying insect biomass found in nature reserves in Germany – about 75% loss in 26 years.

In the 21st century, there appears to be a widespread decline in the number of insects. About 40% of species are threatened by extinction and the types most affected include ants, bees, butterflies, moths and wasps. While some species such as flies and cockroaches might increase as a result, the total biomass of insects is decreasing by about 2.5% per year. The phenomenon is due to multiple factors including habitat destruction, pesticides, introduced species and climate change.

Reviews and studies

In 2012, the Zoological Society of London produced a survey of the prospects of the world's invertebrates: Spineless. It estimated that about 20% of all species were threatened with extinction and that species with the least mobility and smallest ranges were the most at risk.

A comparison of the amount of arthropods in the El Yunque National Forest showed a large decline from 1976 to 2012. Depending on the method of collection, the declines ranged from a factor of 4 to 60. A corresponding decline in the number of insect-eating species such as birds, frogs and lizards was also observed. The decline was attributed to a rise in the average temperature as tropical insect species cannot tolerate a wide range of temperatures.

A 2014 review in Science – Defaunation in the Anthropocene – found that "Of all insects with IUCN-documented population trends, 33% are declining ... Globally, a compiled index of all invertebrate population declines over the past 40 years shows an overall 45% decline".

In 2016, the Entomologischer Verein Krefeld produced a report from their long-term records of insect collections in nature reserves in Germany. This showed that, in the period 1990 to 2016, there had been a decline of 75% in the amount of flying insects.

A 2018 study of rainforests in Puerto Rico reported "biomass losses between 98% and 78% for ground-foraging and canopy-dwelling arthropods over a 36 year period, with respective annual losses between 2.7% and 2.2%"

In 2019, a systematic review of the issue – Worldwide decline of the entomofauna – was published in the journal Biological Conservation. This analysed 73 reports and studies and found that, overall, there were "dramatic rates of decline".

From our compilation of published scientific reports, we estimate the current proportion of insect species in decline (41%) to be twice as high as that of vertebrates, and the pace of local species extinction (10%) eight times higher, confirming previous findings (Dirzo et al., 2014). At present, about a third of all insect species are threatened with extinction in the countries studied (Table 1). Moreover, every year about 1% of all insect species are added to the list, with such biodiversity declines resulting in an annual 2.5% loss of biomass worldwide (Fig. 2).

— Francisco Sánchez-Bayo, Kris Wyckhuys, "Worldwide decline of the entomofauna", Biological Conservation (2019)

Limitations of studies

In their 2019 systemic review, Sánchez-Bayo & Wyckhuys pointed out that most scientific and public attention was focused on the conservation of larger, charismatic vertebrates, that insect biodiversity was low on the agenda and that few studies had been done on such insect groups as Diptera, Orthoptera and Hemiptera. Data from the past from which to calculate trends was largely unavailable, and what did exist mostly related to Western Europe and North America, with the tropics and southern hemisphere being under-represented. The insect studies that had been undertaken were largely concentrated on the more popular insect groups: butterflies and moths, bees, dragonflies and beetles.

A reason that studies are limited is that the science of studying insects – entomology – is itself in decline. General biology courses in college give less attention to insects and the number of biologists specialising in entomology is reducing as other specialities such as genetics expand.

Studying insect populations tends to be done by collecting them and killing them in traps. This is an ethical problem for conservationists.


Responses

A March 2019 statement by the Entomological Society of America said there is not yet sufficient data to predict an imminent mass extinction of insects. They did though agree that the various studies finding declines are "very concerning". Entomology professor Simon Leather suggested that reports of an "Ecological Armageddon" may be exaggerated and believes more funding is needed, to allow better collection of long term data on the decline.

Conservation measures

Following the 2016 report of the Entomologischer Verein Krefeld and other studies, the German environment ministry – the BMU – started its Action Program for Insect Protection (Aktionsprogramm Insektenschutz). This initially contained nine goals:

  1. "Promote insect habitats and structural diversity in the agricultural landscape"
  2. "Restore and connect habitats for insects in other landscape areas"
  3. "Strengthen protected areas as habitats for insects"
  4. "Reduce the use of pesticides"
  5. "Reduce inputs of nutrients and pollutants in soil and water"
  6. "Reduce light pollution"
  7. "Deepening research - multiplying knowledge - closing gaps"
  8. "Improve funding - create incentives"
  9. "Promote the commitment of society"

In a 2019 paper, scientists Olivier Dangles and Jérôme Casas suggested previous attempts to arrest the repeatedly reported "massive insect decline" have been largely ineffective. They argue that the best approach may be for the global policy making community to transition from the current "insects as providers of ecosystem-services" view to one that see "insect as solutions for SDGs". They list 100 studies and other references showing how insects can assist with meeting the Sustainable Development Goals

The Entomological Society of America advise that measures regular people can take include maintaining plant diversity in their gardens, and leaving "natural habitat, like leaf litter and dead wood."

Citizen science is used to monitor insect populations. People have noticed a decline in the number of insects splattered on car windshields when they drive across their country – the windshield phenomenon. Phone apps such as iNaturalist can be used to photograph and identify specimens and these are being used in programs such as the City Nature Challenge. Activities and projects may focus upon a particular type of insect such as National Moth Week and monarch butterfly conservation in California.

See also

References

  1. ^ Hallmann, CA; Sorg, M; Jongejans, E; Siepel, H; Hofland, N; Schwan, H (18 October 2017), "More than 75 percent decline over 27 years in total flying insect biomass in protected areas", PLoS ONE, 12 (10), doi:10.1371/journal.pone.0185809{{citation}}: CS1 maint: unflagged free DOI (link)
  2. McGrath, Matt (11 February 2019), Global insect decline may see 'plague of pests', BBC {{citation}}: Cite has empty unknown parameter: |1= (help)
  3. ^ Sánchez-Bayo, Francisco; Wyckhuys, Kris A.G. (31 January 2019), "Worldwide decline of the entomofauna: A review of its drivers", Biological Conservation, 232: 8–27, doi:10.1016/j.biocon.2019.01.020
  4. ^ Damian Carrington (10 February 2019), "Plummeting insect numbers 'threaten collapse of nature'", The Observer
  5. Vogel, Gretchen (10 May 2017), "Where have all the insects gone?", Science
  6. Collen, Ben; Böhm, Monika; Kemp, Rachael; Baillie, Jonathan E. M., eds. (2012), Spineless – Status and trends of the world's invertebrates (PDF), Zoological Society of London, ISBN 978-0-900881-70-1
  7. Borrell, Brendan (4 September 2012), "One Fifth of Invertebrate Species at Risk of Extinction", Scientific American {{citation}}: Cite has empty unknown parameter: |1= (help)
  8. Lister, Bradford C.; Garcia, Andres (October 2018), "Climate-driven declines in arthropod abundance restructure a rainforest food web", Proceedings of the National Academy of Sciences, 115 (44), doi:10.1073/pnas.1722477115
  9. Guarino, Ben (15 October 2018), "'Hyperalarming' study shows massive insect loss", The Washington Post {{citation}}: Cite has empty unknown parameter: |1= (help)
  10. Jarvis, Brooke (27 November 2018), "The Insect Apocalypse Is Here", The New York Times
  11. Dirzo, Rodolfo; Young, Hillary; Galetti, Mauro; Ceballos, Gerardo; Isaac, Nick; Collen, Ben (25 July 2014), "Defaunation in the Anthropocene" (PDF), Science, 345 (6195): 401–406, doi:10.1126/science.1251817
  12. McGrane, Sally (4 December 2017), "The German Amateurs Who Discovered 'Insect Armageddon'", The New York Times {{citation}}: Cite has empty unknown parameter: |1= (help)
  13. Lister, BC; Garcia, A. (October 2018), "Climate-driven declines in arthropod abundance restructure a rainforest food web", PNAS, 115: E10397–E10406, doi:10.1073/pnas.1722477115
  14. Alexandra Sifferlin (14 February 2018), "Fewer Scientists Are Studying Insects. Here's Why That's So Dangerous", TIME
  15. Leather, Simon (January 2007), "British Entomology in terminal decline?", Antenna, 31 (4): 192
  16. Gangwani, Kiran; Landin, Jennifer (12 December 2018), "The Decline of Insect Representation in Biology Textbooks Over Time", American Entomologist, 64 (4): 252–257
  17. Blakemore, Erin (12 December 2018), "Insects are disappearing from science textbooks—and that should bug you", Popular Science
  18. Hart, Adam, "Inside the killing jar", The Biologist, 65 (2): 26–29 {{citation}}: Cite has empty unknown parameter: |1= (help)
  19. Fischer, Bob; Larson, Brendan (25 February 2019), "Collecting insects to conserve them: a call for ethical caution", Insect Conservation and Diversity, doi:10.1111/icad.12344
  20. ^ Global Insect Biodiversity:Frequently Asked Questions (PDF), Entomological Society of America, March 2019 {{citation}}: Cite has empty unknown parameter: |1= (help)
  21. Leather, Simon (20 December 2017), ""Ecological Armageddon" – more evidence for the drastic decline in insect numbers", Annals of Applied Biology, 172: 1–3, doi:10.1111/aab.12410
  22. Bélanger, J.; Pilling, D., eds. (2019), The State of the World’s Biodiversity for Food and Agriculture (PDF), Rome: FAO Commission on Genetic Resources for Food and Agriculture, p. 133
  23. Action program insect protection (in German), Bundesministerium für Umwelt, Naturschutz und nukleare Sicherheit, 10 October 2018
  24. Dangles, Olivier; Casas, Jérôme (February 2019), "Ecosystem services provided by insects for achieving sustainable development goals", Ecosystem Services: Science, Policy and Practice, 35: 109–115, doi:10.1016/j.ecoser.2018.12.002
  25. Katherine Roth (15 January 2019), Apps let everyone help track health of insect populations, Associated Press
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