Posted by: recordingsofnature | April 20, 2018

Decline in insect populations – is silence spreading over the land?

Recent research report on significant decline in insect populations. In Germany a 75 percent decline in total flying insect mass has been observed over a duration of 27 years in natural reserves (Hallmann, 2017[1]). Another study reports on a 45 percent decline in invertebrate populations over the past 40 years based on global monitoring data (Dirzo, 2014[2]), see figure below.

F1.large_C

Dirzo, 2014 [2]

The reason behind is not 100% clear, but the obvious suspects are pesticides use, intensive agriculture, shrinking habitats, urbanization, use of fertilizers amongst others. [3], [6]

I think this is disturbing news. A future scenario where major insect populations have collapsed and insects are largely abundant looks quite realistic with the current decline rates. This would be just sad in every aspect. Insects are fundamental drivers of ecosystems, food chains, biological processes and biodiversity.

It is hard to imaging how such decline is going to affect the biosphere and natural world. At a distance, I guess, most could still look quite normal, since many plants could still be growing well, but below this superficial beauty, one would find a very limited and monotone ecosystem, without complexity, substance, nerve or bite. Wild nature could become like over-maintained city parks; tamed and boring, only filled with predictable sounds or eerie silence.

Personally, I have not given a decline of insects much direct thought before reading about this. What I have noticed, however, is a decline in characteristic farmland singing birds; notably skylark, starling, linnet, yellowhammer and others. Looking into the official Danish breeding bird index for these birds [4] and comparing it with the insect index for ‘other invertebrates’[2] there is actually a striking similarity:

linnet and insects3_

At a European scale, the trends for common farmland birds and common forest birds  (EBCC [5]) also show a clear decline for the farmland birds, while forest birds are on a stable level.

european_

Many birds are declining, but there are also examples of bird species which are radically increasing in Denmark, including the insect feeding (and beautifully singing) blackcap, chiffchaff and redstart [4].

gransanger munk rodstj_

So, in the present picture it looks like the main problem regards the farmland. Here the decline of insects and birds seems to be going hand in hand. For forest and other habitats, there is less of a clear overall trend, but still a lot of change with species increasing and declining.

In my view, I strongly suspect certain modern pesticides to be getting a bit too effective and even accumulating and spreading far outside the area where sprayed, causing mass dead of insects in much larger areas and on a much larger scale than intended.  At the same time, more and more land is included for intensive agriculture and urbanization, globally.

In my view, some of the important steps to fight this development will be to:

  • Carry out more systematic monitoring of insects, to be able to understand and address the problem optimally, and to cover up for current lack of systematic long term observations.
  • Use alternatives to chemical pesticides
  • Use highly biodegradable pesticides and identify and ban certain pesticides which are particular problematic to insect populations.
  • Apply pesticides more effectively and in smaller precise amounts, e.g. by use of precision agriculture.
  • Stress the importance of having areas (of significant sizes) of wild and untouched nature.

But, despite many good intentions and efforts, easiest solution in many cases will still just be to use some cheap pesticide. So I am actually not too optimistic for the future. It will likely only go in one direction.

This is definitely a complex topic which I am going to follow closely in the future.

 

All graph data have been extracted and digitized using the http://www.graphreader.com online tool.

[1] Hallmann et. al., More than 75 percent decline over 27 years in total flying insect biomass in protected areas, Oct 2017. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0185809

[2] Dirzo 2014, Science. http://science.sciencemag.org/content/345/6195/401/

[3] Warning of ecological Armageddon after dramatic plunge in insect number, https://www.theguardian.com/environment/2017/oct/18/warning-of-ecological-armageddon-after-dramatic-plunge-in-insect-numbers

[4] Moshøj, C.M., D.P. Eskildsen, T. Nyegaard, M.F. Jørgensen, T. Vikstrøm (2017). Overvågning af de almindelige fuglearter I Danmark 1975-2016. Årsrapport for Punkttællingsprogrammet. Dansk Ornitologisk Forening. https://www.dof.dk/images/projekter/punkttaelling/dokumenter/702884_DOF_Overvaagningsrapport_online.pdf . Latest Danish bird monitoring indexes and data:  http://www.dof.dk/fakta-om-fugle/punkttaellingsprojektet/indeks-og-tendenser

[5] ECBB European indicators (1980-2015) for forest birds, farmland birds and common birds: http://www.ebcc.info/index.php?ID=588 .  Index graphs (1980-2015) for individual European bird species (if you know the Latin name..): http://www.ebcc.info/index.php?ID=587

[6] What’s Causing the Sharp Decline in Insects, and Why It Matters 2016, https://e360.yale.edu/features/insect_numbers_declining_why_it_matters

 

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