Global insect decline may see ‘plague of pests’

  • 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.

A scientific review of insect numbers suggests that 40% of species are undergoing “dramatic rates of decline” around the world. The study says that bees, ants and beetles are disappearing eight times faster than mammals, birds or reptiles but researchers say that some pest species, such as houseflies and cockroaches, are likely to boom.

The general insect decline is being caused by intensive agriculture, pesticides and climate change.

Insects make up the majority of creatures that live on land, and provide key benefits to many other species, including humans. They provide food for birds, bats and small mammals; they pollinate around 75% of the crops in the world; they replenish soils and keep pest numbers in check.

Many other studies in recent years have shown that individual species of insects, such as bees, have suffered huge declines, particularly in developed economies but this new paper takes a broader look. The study is published in the journal Biological Conservation and reviews 73 existing studies from around the world published over the past 13 years.

The researchers found that declines in almost all regions may lead to the extinction of 40% of insects over the next few decades. One-third of insect species are classed as endangered. “The main factor is the loss of habitat, due to agricultural practices, urbanisation and deforestation.” said lead author Dr Francisco Sánchez-Bayo, from the University of Sydney. “Second is the increasing use of fertilisers and pesticides in agriculture worldwide and contamination with chemical pollutants of all kinds. Thirdly, we have biological factors, such as invasive species and pathogens; and fourthly, we have climate change, particularly in tropical areas where it is known to have a big impact.”

Some of the highlights of study include the recent, rapid decline of flying insects in Germany, and the massive drop in numbers in tropical forests in Puerto Rico, linked to rising global temperatures.

The authors are concerned about the impact of insect decline up along the food chain. With many species of birds, reptiles and fish depending on insects as their main food source, it’s likely that these species may also be wiped out as a result.

Cockroaches and houseflies may thrive while others decline, say experts
While some of our most important insect species are in retreat, the review also finds that a small number of species are likely to be able to adapt to changing conditions and do well.

More research is also badly needed as 99% of the evidence for insect decline comes from Europe and North America with almost nothing from Africa or South America.

Ultimately, if huge numbers of insects disappear, they will be replaced but it will take a long time.

To read the full paper see visit here

Worldwide decline of the entomofauna: A review of its drivers
Francisco Sánchez-Bayoa and Kris A.G.Wyckhuysbcd
https://doi.org/10.1016/j.biocon.2019.01.020

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