The following is an excerpt from Wikipedia on insect collapse:
“Several studies report a substantial decline in insect populations. Most commonly, the declines involve reductions in abundance, though in some cases entire species are going extinct. The declines are far from uniform. In some localities, there have been reports of increases in overall insect population, and some types of insects appear to be increasing in abundance across the world. A 2020 meta-analysis published in the journal Science found that globally, terrestrial insects appeared to be declining in abundance at a rate of about 9% per decade, while the abundance of freshwater insects has increased by 11% per decade.
Some of the insects most affected include bees, butterflies, moths, beetles, dragonflies and damselflies. Anecdotal evidence has been offered of much greater apparent abundance of insects in the 20th century; recollections of the windscreen phenomenon are an example.
Possible causes of the decline have been identified as habitat destruction, including intensive agriculture, the use of pesticides (particularly insecticides), urbanization, and industrialization; introduced species; and climate change. Not all insect orders are affected in the same way; many groups are the subject of limited research, and comparative figures from earlier decades are often not available.
In response to the reported declines, increased insect related conservation measures have been launched. In 2018 the German government initiated an “Action Programme for Insect Protection”, and in 2019 a group of 27 British entomologists and ecologists wrote an open letter calling on the research establishment in the UK “to enable intensive investigation of the real threat of ecological disruption caused by insect declines without delay”. 
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