Scientists have discovered only a tiny fraction of living insect species, but up to as many as 20 million insect species may exist

Amazing stuff!

"... according to a new study ... Using statistical methods borrowed from another field, a team of entomologists estimates there may be as many as 20 million insect species on our planet—more than three times the previous estimate. ...

Scientists have long debated exactly how many insect species there are, with the previous consensus being about 6 million. 

Over the past 3 centuries, entomologists have described about 1 million insect species, but finding and describing them all would be a daunting—if not impossible—task. ...

To obtain an improved estimate of insect diversity, Colwell and colleagues studied years of data from insect surveys in Costa Rica’s Guanacaste National Park and applied statistical methods borrowed from epidemiology. The researchers started by taking a closer look at a subfamily of parasitoid wasps known as Microgastrinae, which infamously lay their eggs inside living caterpillars. These wasps are extremely well-studied: Scientists have described about 3000 species of Microgastrinae, many of which are found in Costa Rica. So, the team decided to test how well insect surveys within the park have captured the diversity of the wasps living there.

Over the past several years, scientists conducting surveys of flying insects in the park have identified 388 species of Microgastrinae within a core set of traps and 578 within an additional set. Independently, when scientists looked at caterpillars that had been parasitized within the park, they identified 889 wasp species.

However, when Colwell and his colleagues examined these data sets, they were surprised to find little overlap in the species captured with traps and by examining caterpillars. That mismatch showed both methods must only be tallying a fraction of the total number of Microgastrinae species within the park. To estimate that total, the researchers used a statistical method developed by epidemiologists to estimate the size of a population affected by a disease based on incomplete tallies of the ill—as if the true number of wasp species was like the true number of sick people in an outbreak. The approach indicated the park is home to a whopping 2394 Microgastrinae species. ..."

From the significance and abstract:

"Significance

For more than 40 y, entomologists have attempted to estimate the number of insect species on Earth, with the current consensus—the figure most experts accept—at about six million. Using genetic information (DNA barcodes) for 1.6 million individual tropical insects, a deep census of a highly diverse group of parasitoid wasps, and powerful statistical strategies, we conservatively estimate that the true number of insect species is at least 14 to 20 million—two to three times higher than current estimates. Already known to be the most diverse group of animals, a doubling or tripling of estimated insect diversity has profound implications for our understanding of the scale, richness, and future of biodiversity on Earth.

Abstract

Estimating the number of insect species on Earth is a daunting challenge. The current consensus estimate—about six million species—is likely far too low, as we will show.

Our estimate of the global number of insect species rests on a sample of more than 1,600,000 DNA-barcoded insect specimens representing 53,945 species from 15 “core” Malaise traps deployed in dry forest, cloud forest, and rainforest ecosystems of the Área de Conservación Guanacaste (ACG) in Costa Rica. Even this massive sample fails to reveal the full extent of ACG insect species richness. To estimate total ACG insect richness, we adjust the observed count of insect species by an “undersampling ratio,” computed for a hyperdiverse subfamily of parasitoid wasps (Braconidae: Microgastrinae).

The ratio compares microgastrine richness from the core Malaise traps to a lower-bound estimate of true microgastrine richness—including undetected species—based on 21,669 specimens from three sources: the 15 core Malaise traps, 15 “peripheral” Malaise traps spanning all three ecosystems, and 11,373 DNA-barcoded specimens reared from some 1,500 species of microgastrine-parasitized caterpillars (Lepidoptera).

To estimate global insect richness, we apply Earth/ACG ratios for tree species and several animal taxa to upscale our estimate of ACG insect richness (nearly 333,000 species). Adopting conservative assumptions, we reach an estimate of 14 to 20 million insect species on Earth, depending on the upscaling group—two to three times the current consensus estimates. Upscaling instead from a point estimate of ACG richness with a wide CI, global estimates reach nearly 30 million species."

Scientists have discovered only a tiny fraction of living insect species | Science | AAAS "About 1 million insect species have been described, but a new analysis suggests tens of millions more may be out there"

Constructing a lower-bound estimate of the global number of insect species on a hyperdiverse empirical foundation (open access)