Where have all the insects gone?

A new study shows an alarming decline of insects across nature reserves in Germany. This has led to warnings of 'ecological Armageddon’. We need to act now, rather than delaying to gather more information or to argue over the causes.
Flying insects caught in a malaise trap, used by entomologists to collect samples. Photograph: Entomologisher Verein Krefeld

Amateur entomologists from the Krefeld Entomological Society have been trapping insects on nature reserves in for 27 years (refs 1, 2, 3). They used Malaise traps which are large, tent-like structures: insects fly into the tent wall and are funnelled into a collecting vessel attached to highest point.

Malaise Trap
The original uploader was Ceuthophilus at English Wikipedia - Transferred from en.wikipedia to Commons by Richard001 using CommonsHelper., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=6317383

They sampled 88 sites on a total of 15,249 trapping days between 1989 and 2014, catching some 51kg of insects.
The grim finding is that the biomass of flying insects in German nature reserves has declined by 80% over these 27 years. In the early days of the study, a typical catch was 9g of insects per day; by 2014 this was down to an average of 1g per day.
These are protected sites, so what is going on?
Analysis has shown that the decline is not due to changing land use around the sites, nor to site management regimes. Variation is weather accounts for only a small amount of the change.
Nobody knows the reasons, but there are several hypotheses:

  • Significant habitat destruction in the 20th century as a result of industrial farming led to an “extinction debt”, as the creatures left of fragmented nature reserves are not viable in the long term.
  • Or it could be the increased use of pesticides, including the systemic and highly toxic  neonicotinoids, which were introduced in the 1990s. These could be contaminating the nature reserves directly, or making the surrounding areas inhospitable to insects (acting as a ‘population sink’).
This decline is alarming, because if the insects disappear the environment will descend into chaos. Insects are vital parts of the food chain (e.g. for birds and bats), they pollinate trees and plants, they help with the decay of dead matter, and they act as pests to maintain an environmental balance.
This is a case where we cannot afford to wait for more information before doing something. There’s already enough evidence to show that “landscape-scale” approaches to the environment are needed - connecting up fragmented habitats. And we know that pesticides - not least the neonics - are harmful to insects, so why not curtail their use now?

 References

  1. Hallmann CA, Sorg M, Jongejans E, Siepel H, Hofland N, Schwan H, et al. (2017) More than 75 percent decline over 27 years in total flying insect biomass in protected areas. PLoS ONE 12 (10): e0185809. https://doi.org/10.1371/journal. Pone.0185809
  3. British Wildlife, Vol. 29 No. 1 Oct 2017, Editorial by Dave Goulson

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