A new study reveals that the planet could hold 14.2 million to 20.3 million insect species, far above the long-accepted figure of about 6 million.
The findings published in the journal Proceedings of the National Academy of Sciences.
Scientists have formally described about 1.2 million insect species so far, leaving the vast majority still unknown. The new study highlights how much remains to be discovered and underscores the urgency of documenting insect biodiversity before more species disappear.
The researchers carried out a large-scale insect survey in the Area de Conservacion Guanacaste (ACG), a nature reserve of 169,000 hectares in northwestern Costa Rica in Central America. It includes dry forest, cloud forest, and rainforest, making it one of the world's richest natural laboratories for studying insects.
Researchers focused on Microgastrinae, a highly diverse group of parasitoid wasps (a taxonomic rank between family and genus) that lay their eggs inside caterpillars. As the wasp larvae develop, they consume the caterpillar from within before emerging. Because these wasps are exceptionally diverse and closely associated with their hosts, they provide an effective way to estimate overall insect richness.
To collect Microgastrinae, the team deployed 15 Malaise traps—tent-like insect capture devices—in both the core and peripheral areas of the Guanacaste Conservation Area. Altogether, the researchers captured 1.63 million tropical insects.
Using DNA barcoding, a technique that distinguishes species by analysing short DNA sequences, the researchers identified 53,945 insect species from the core-area Malaise traps alone.
Combining insects collected from Malaise traps in both the core and peripheral areas with those obtained from caterpillars, the team found a total of 1,414 Microgastrinae species.
Applying statistical methods to the detected species, the researchers estimated that the actual number of insect species present in the Guanacaste Conservation Area is around 332,846.
To estimate global insect diversity, the researchers then compared the number of tree species in the reserve between 1,200 and 1,500—with the roughly 73,000 tree species known worldwide.
Using trees as a reference group to scale up insect diversity, they arrived at a preferred estimate of 20.3 million insect species globally.
Alternative calculations based on trees, amphibians, mammals and saturniid moths produced estimates ranging from 14.2 million to 20.3 million species, which the researchers describe as conservative.
The findings suggest that earth's insect diversity is far richer than previously recognised.
As human activities drive an unprecedented global decline in insect populations, the researchers believe their work offers important clues for conserving the insect diversity that still remains.