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A mass extinction is underway, but many people remain oblivious to it. One reason involves insects, which often escape our attention except when they bother us.
In addition to honey bees and beautiful butterflies, insects tend to be unloved creatures, however we should pay much more attention to them, as their situation is quite dire in Europe, the United States, and beyond. In the UK, for example, a third of the 353 species recently surveyed, including wild bees and flying flies, have dropped in their ranges. Some insect populations have plummeted so precipitously that they risk going completely extinct in England, Scotland and Wales.
Numerous studies have painted similarly bleak pictures. In fact, experts have warned of the unfolding "insect apocalypse." Bees and bumblebees have been among the insects particularly affected by human-caused environmental stressors, including climate change and the widespread use of pesticides. The massive death of insects should be a matter of serious environmental concern because the disappearance of the creepy critters will have collateral effects for entire ecosystems: plants will lose their pollinators and various animals such as birds will lose their main sources of food.
Now a new study, published in the journalScience , gives us more information on the state of insects around the world. An international team of researchers, whose members work at two German institutions, set out to understand the severity of the problem by looking at studies of insect abundance from around the world. They collected data from 166 long-term surveys at 1,676 sites between 1925 and 2018 with the goal of understanding trends in insect population changes over time.
"Overall, we found considerable variation in trends even between adjacent sites, but an average decrease in the abundance of terrestrial insects by 9% per decade and an increase in the abundance of freshwater insects by 11% per decade," they write. the researchers in their study.
“Both patterns were largely driven by strong trends in North America and some European regions. We found some associations with potential drivers (eg land use drivers), and trends in protected areas tended to be weaker ”
Specifically, researchers have detected a global decline of 0.92% each year in populations of terrestrial insects such as butterflies, grasshoppers and ants. That annual rate of decline adds to a total decline of 24% in just three decades and 50% fewer insects in 75 years. Among the main causes of the dramatic decline are extensive agriculture, habitat loss and climate change.
This is the bad news for insects. But there are good news.
During the same period, the number of insects that live in fresh water, such as mosquitoes and flies, increased at a similar rate, by 1.08% each year on average. According to experts, this could be due to more effective water protection measures in many countries. Population trends can also be highly variable, they explain, with areas less affected by human activities showing more robust insect population health than nearby more impacted areas.
"For example, in countries where many insect surveys have been conducted, such as Germany, the United Kingdom, and the United States, some locations experienced declines, while others very close by showed no change, or even increased," says a statement on the findings. “The decline in insects was strongest in some parts of the US (West and Midwest) and in Europe, particularly Germany. For Europe as a whole, the trends turned more negative on average over time, with the strongest declines since 2005. ″
People in many European countries have observed the decline in the rate of flying insects simply by finding fewer squashed insects on their car windshields while driving.
"Our analysis shows that flying insects have decreased on average," says Jonathan Chase, professor of ecology at the German Center for Integrative Biodiversity Research, who co-authored the study. "However, most insects are less visible and live out of sight, on the ground, in the treetops or in the water."
And many of these less conspicuous insects, like dwarfs and mayflies, are still doing relatively well. Their populations appear to have increased 1.08% each year, corresponding to an overall increase of 38% in 30 years. This positive trend has been especially notable in northern Europe, Russia, and the western part of the US.
"These numbers show that we can reverse these negative trends," says Chase. “In the last 50 years, various steps have been taken to clean up our polluted rivers and lakes in many parts of the world. This may have allowed many freshwater insect populations to recover. It makes us hope that we can reverse the trend of the stocks that are currently declining. "
Insect abundance trends are complex phenomena, says Ann Swengel, a study co-author who has been studying butterfly populations at hundreds of sites in Wisconsin and other US states.
“We have seen a lot of decline, even in many protected sites. But we have also seen some places where butterflies are still doing well, ”says Swengel. “It takes many years and a lot of data to understand both failures and successes, species by species and site by site. Much is beyond anyone's control, but the choices we make at each site really matter. "