Climate change and intensive agricultural practices have wiped out nearly half of the insects in some parts of the world, a report published Wednesday suggests.
The warning is the first time a study has tested the link between rising temperatures and land use, and swingeing losses across numerous insect groups around the world.
Limited available evidence means the established 49 per cent reduction "may only represent the tip of the iceberg", too, said the lead author, Dr Charlie Outhwaite, UCL Centre for Biodiversity & Environment Research.
Scientists believe the phenomena pose a severe threat to human existence.
“Losing insect populations could be harmful not only to the natural environment, where insects often play key roles in local ecosystems, but it could also harm human health and food security, particularly with losses of pollinators," said Dr Outhwaite.
Humans have been instrumental in causing the losses which are now rebounding upon them, the study found.
“Many insects appear to be very vulnerable to human pressures, which is concerning as climate change worsens and agricultural areas continue to expand," said Dr Outhwaite.
"Our findings highlight the urgency of actions to preserve natural habitats, slow the expansion of high-intensity agriculture, and cut emissions to mitigate climate change."
More biodiversity, more insects
The researchers analysed a large dataset of insect abundance and species richness from areas across the globe, including three-quarters of a million records for about 20,000 insect species.
The team compared insect biodiversity in different areas depending on how intensive agriculture is in the area, as well as how much historic climate warming the local area has experienced.
They found that in areas with high-intensity agriculture and substantial climate warming, the number of insects was 49 per cent lower than in the most natural habitats with no recorded climate warming, while the number of different species was 29 per cent lower.
Tropical areas saw the biggest declines in insect biodiversity linked to land use and climate change.
Conversely, in areas where there is less intensive land use and climate degradation, losses were pared.
Where 75 per cent of the land was covered by natural habitat, insect abundance only declined by 7 per cent, compared to a 63 per cent reduction in comparable areas with only 25 per cent natural habitat cover.
The worst is yet to come?
The researchers believe insect declines due to human influences may be even greater than their findings suggest. This is because many areas with long histories of human impacts would have already seen biodiversity losses before the start of the study period. The study also did not account for the effects of other drivers such as pollution.
“We need to acknowledge how important insects are for the environment as a whole, and for human health and wellbeing, in order to address the threats we pose to them before many species are lost forever,” said joint first author, Peter McCann.
The research was published in Nature journal.