(CNN)There has been an overwhelming drop in the number of wild bee species that are reported in public records over the past 30 years, according to a new study.
Researchers looked at bee records in the Global Biodiversity Information Facility, an online biodiversity data collector, and found there were about 25% less bee species reported between 2006 and 2015 compared to the 1990s.
Study author Eduardo Enrique Zattara, adjunct researcher at Argentina's National Scientific and Technical Research Council, realized in 2018 that he could track the global population of bee species using the online data to see long-term trends of bee populations.
His research team began searching for possible explanations as to why so many bees are missing.
Zattara first looked at reasons the data could be artificially low, meaning that the data might not accurately reflect the number of bee species.
One hypothesis is that less people are reporting on bee species, which means there would be less data inputted into the system. Bee trackers might also be reporting only well-known bee species as rarer ones become harder to find or identify.
"We analyzed several of these alternative reasons, but could not find any that on its own could explain such a large drop in the number of reported species," Zattara said.
With a decline in plants and animal populations on the planet, including the honeybee, a decline in bee diversity is the most likely culprit for the drop in reported species numbers, he said.
Why could bees be dying?
Loss of habitat and climate crisis could be playing a role in the declining numbers, said Kirsten Shoshanna Traynor, research associate at the Global Biosocial Complexity Initiative at Arizona State University, who was not involved in the study. As more land is urbanized, bee habitats are destroyed, which kills the next generation of bees.
The climate crisis may be forcing bees out of their native climate zones and exposing them to dangerous weather events, Zattara said.
He also said invasive bee species could be to blame. When foreign bees are introduced to a particular area, they can kill off the native bees.
Looking forward, he wants to study a case in which a foreign bee was introduced in Patagonia so he can research how to reverse the damage.
"Our insights could then be applied to prevent or reverse the decline of wild bees on other parts of the world," Zattara said via email.
Consequences of the decline
Wild bees are responsible for the pollination of 85% of the world's crops, according to the study, which was published Friday in the One Earth journal.
Many of the foods people enjoy, such as avocados and nuts, rely on pollination, Traynor said.
Plants have a difficult time moving the pollen, which is the male part of the plant, to the female part, so the plant can be fertilized and reproduce. Traynor calls bees "plant sex on wings" because they are great at pollinating plants.
If there is a decline in wild bee populations, it will be significantly harder for plants to reproduce.
"As bees disappear, so do the animals that depend on them and the plants they pollinate," Traynor said.