Insect species are most diverse in the tropics, but are largely unresearched, with many species not described by science. But entomologists believe abundance is being impacted by climate change, habitat destruction and the introduction of industrial agribusiness with its heavy pesticide use.A 2018 repeat of a 1976 study in Puerto Rico, which measured the total biomass of a rainforest’s arthropods, found that in the intervening decades populations collapsed. Sticky traps caught up to 60-fold fewer insects than 37 years prior, while ground netting caught 8 times fewer insects than in 1976.The same researchers also looked at insect abundance in a tropical forest in Western Mexico. There, biomass abundance fell eightfold in sticky traps from 1981 to 2014. Researchers from Southeast Asia, Australia, Oceania and Africa all expressed concern to Mongabay over possible insect abundance declines.In response to feared tropical declines, new insect surveys are being launched, including the Arthropod Initiative and Global Malaise Trap Program. But all of these new initiatives suffer the same dire problem: a dearth of funding and lack of interest from foundations, conservation groups and governments. In recent months a debate over whether a global insect apocalypse is underway has raged in the mainstream media and among researchers. To assess the range of scientific opinion, Mongabay interviewed 24 entomologists and other scientists working on six continents, in more than a dozen countries, to better determine what we know, what we don’t, and most importantly — what we should do about it. This is part 3 of a 4-part exclusive series written by Mongabay senior contributor Jeremy Hance. Click on the following links to read part 1 and part 2. Early in the 1980s, a beetle-mad scientist named Terry Erwin decided to count the number of Coleoptera species — the insect order containing beetles and weevils — chilling in the rainforest canopy. He was trying to answer a really big question: how many total species live on Earth? And he figured beetles, one of the planet’s super-families, was the place to start. So he packed off to Panama and picked 19 trees of a single species, Luehea seemannii. Then, he bombed them with pesticide — a method dubbed “fogging,” well known to entomologists and exterminators. Counting the dead, Erwin identified 988 distinct beetle species. Then he did some back-of-napkin-calculations, estimating how many of those beetles might be endemic to Luehea seemannii, and how many rainforest tree species there might be in the world, etc., etc., until he concluded there could be 30 million tropical arthropod species on the planet. Most scientists today have considerably curbed that estimate, putting the total count for all species of plant and animal at around 8+ million. But even though that total is smaller, Erwin’s work proved vital in two ways: it showed that insect diversity was far greater than anyone had then imagined in tropical rainforests, and that rainforests were among the most biodiverse places on the planet. In other words, when it comes to the insect kingdom, the tropics are king.