'Super Cool' Mapping Tracks Down Tiny Invaders

Scientists in search of insects can spend 1,000 hours checking roughly 10,000 trees across 40 acres. Or, with a more convenient approach, they can do the same in about an hour. More and more, researchers are turning to remote sensing technology to ease the burden of searching landscapes for difficult-to-spot plants and wildlife. For more than a decade, they've spoken of the potential of lidar (light detection and ranging), traditionally used to document archaeological sites, to uncover invasive species, including an invasive grass that fuels forest fires in Australia. And in a study published March 12 in Methods in Ecology and Evolution, a team describes how lidar was used to identify tiny ants in Kenya's whistling thorn acacia trees with more than 80% accuracy.

"It's super cool; it does exactly what they say," University of Michigan ecologist Nate Sanders, who wasn't involved in the study, tells Science. "They're using really efficient technology to sample biodiversity they otherwise wouldn't be able to sample." Harvard University behavioral ecologist Naomi Pierce studies the relationship between acacia trees and the ants that occupy them, but finding the ants is difficult. Researchers hoped lidar might present a better way. As Science explains, Crematogaster nigriceps ants chew leaves from a tree's outer branches, shrinking the canopy and preventing flowering. This leaves an infected tree looking quite different from others nearby.

Researchers trained a lidar system to look for trees occupied by the ants, then sent up a lidar-equipped drone to scan 40 acres that were home to 9,680 acacia trees. They then did a field survey of the same area and compared the data. The lidar survey detected the ant-occupied trees with 82% accuracy, according to the study. As Pierce tells Science, "In one hour, you can do what it took us 1,000 hours to do." The technology has the potential to track tree pests like hemlock woolly adelgid and powdery mildew, which also alter the shape of a tree, freeing up funds to address the problems. But it could also be used to search for invasive species or those at risk of extinction. As Sanders notes, "You could survey all of East Africa in a week, who knows?" (More insects stories.)