How dire is the problem? Koh and his colleagues decided to find out by modeling what wild bee populations look like now—and how this might change in coming years. They used publicly available satellite data to classify land cover in the US, dividing the country up into use areas that included agricultural land, grassland, and more. Then the researchers asked fourteen experts in bee ecology to assess which areas could serve as decent habitats for the roughly 4,000 species of wild bees that live in the US today. This data, combined with information from field studies of bees and their habitats, formed the basis for the hot spot maps you see in this article.

After their analysis, the research team found that wild bee populations have declined in 23 percent of the US over the past several years. And this has implications for our future food security. Koh and his colleagues show that 39 percent of croplands that depend on bee pollination are in areas where wild bee numbers are shrinking (see map at the top of the article).

Koh told Ars via e-mail that domestic honey bees can make up for some of these losses, but "we need to do a better job of integrating wild bees in crop pollination systems." Especially given that honey bees are also suffering dramatic losses, we can't afford to lose wild bees that Koh says are "very efficient and give us their pollination for free—all we need to do is provide them with a suitable habitat."

He and his colleagues hope that these maps of wild bee decline can help government agencies and land planners determine the best locations for bee habitat conservation. The fates of our delicious fruits and vegetables may depend on it.

Proceedings of the National Academy of Science, 2015. DOI: 10.1073/pnas.1517685113 (About DOIs).