Climate change, insecticides, herbicides, light pollution, invasive species and changes in agriculture and land use are causing Earth to lose probably 1% to 2% of its insects each year, said University of Connecticut entomologist David Wagner, lead author in the special package of 12 studies in Monday's Proceedings of the National Academies of Sciences written by 56 scientists from around the globe.
Wagner said scientists need to figure out if the rate of the insect loss is bigger than with other species.
Co-author and University of Illinois entomologist May Berenbaum, a National Medal of Science winner, said, "Insect decline is kind of comparable to climate change 30 years ago because the methods to assess the extent, the rate (of loss) were difficult.".
Two well known ones - honeybees and Monarch butterflies - best illustrate insect problems and declines, he said.
Scientists have identified 1 million insect species, while probably 4 million more are still to be discovered, Berenbaum said.
University of Delaware entomologist Doug Tallamy, who wasn't part of the studies, said they highlight how the world has "spent the last 30 years spending billions of dollars finding new ways to kill insects and mere pennies working to preserve them."
"The good news is, with the exception of climate change, individuals can do much to reverse insect declines," Tallamy said in an email