The global decline of insects in recent decades has been evidenced by numerous studies, and is caused by human activity.
This decline has been particularly well documented in flying speciesand in areas of North America and Europe.Losses have also been recorded for other insect groups and in different parts of the world. The following data can give an idea of the magnitude of the problem and the lack of knowledge that still exists for various insect groups:
- It is estimated that only around a 20 % of all insect species on the planet have been described.
- According to the International Union for Conservation of Nature (IUCN), in 2013, 33 % of the insects with known demographic trends was in decline.
- The European Red List of Bees includes 1942 species, of which 77 are threatened. In addition, 1101 species do not have sufficient information to determine their conservation status.
- The European Red List of Butterflies contains 435 species, of which 37 are threatened and 4 have insufficient data to assess their conservation status.
The main causes of threat linked to insect decline are:
1. Habitat degradation
The conversion of wild areas in areas of human activity, such as agriculture, or in residential areas, is the greatest threat to biodiversity.
Tropical forests are home to the highest species richness of insects on the planet. Given that the insect fauna in these areas is not fully known, it is very likely that deforestation is causing the loss of some species that have not yet been scientifically described.
The intensification of agriculture brings with it a set of practices that are highly detrimental to insects such as the use of pesticidesthe monocultures and the cultivation of genetically modified plants that produce toxins against insects.
Finally, the small farms that previously maintained semi-natural grasslandshave been replaced in many cases by commercial areas, residential areas, or intensive agricultural areas. In other cases, these farms have been abandoned and have been transformed into forests,. These changes in land use lead to the loss of species, or, if habitats are not deforested, to their replacement by other species.
2. Use of insecticides
Although insecticides are designed to eliminate specific pests, these products affect many non-target species, and their mixtures can have effects on many other species. unknown on other insects. In addition, because of their persistence and dispersal in the environment, they can contaminate aquatic and wild habitats.
In addition to the lethaleffects, insecticides and other pesticideshave sub-lethal effects in insects such as stress, disorientation, or weakening of the immune system, which can reduce insect populations.
3. Climate change
Climate change affects insects in a variety of ways, including rising temperatures, extreme weather events, droughts and alterations in rainfall patterns, as well as the flora on which they depend. This phenomenon could become the biggest threat for insects in the future, along with habitat loss.
4. Nitrification
The burning of fossil fuels releases nitrogen into the atmosphere, which is subsequently deposited in the soil. Nitrogen is often a limiting nutrient for vegetation, so an increase in nitrogen in the soil leads to changes in plant communities. Approximately half of all known insect species feed on plants, so these changes in the distribution and abundance of plant species directly affect the insects that depend on them.
5. Alien and invasive species
The introduction of alien species of plants, animals and pathogens is another threat to local insects, especially on islands and in areas of high human activity.
6. Light pollution
Although studying the effect of light pollution in isolation, without taking into account other factors such as habitat destruction, is complex, it has been shown that this pollution negatively affects the nocturnal insects. Among other effects, artificial light sources disorientate insects, causing them to fly around themand making them more vulnerable to predators.
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