If you want to save bumble bees, plant these flowers in your yard

(CNN)Researchers have figured out which plant species bumble bees prefer to include in their diets, providing advice to those wishing to help with bee conservation efforts.

During the summer months of 2015 to 2016, authors captured bumble bees on more than 100 plant species across more than 400 plots in the Plumas National Forest in California -- a mountainous, meadowy area with wildlife habitats near running water, where bumble bees are abundant.
The findings, published Tuesday in the journal Environmental Entomology, revealed that the most popular plant species among the bees were Oregon checker-mallow and mountain pennyroyal flowers.
    Many plants rely on bees as natural pollinators to produce some of nature's most nutritious foods. However, species of North American bumble bees have significantly declined in population in recent decades. Between April 2015 and April 2016, beekeepers in the US lost 44% of their colonies.
    Jerry Cole, lead author of the research and biologist at the Institute for Bird Populations in California, said there are a few potential reasons behind the declines: competition with other insect species, transfer of parasites from honey bees to bumble bees, loss of floral resources, or a mismatch between the phenology of plant species and the phenology of bumble bee species.
    Phenology is defined by how plants and animals function in their environments in different seasons. Making sure the two are in sync is important, as our food supply depends on the timing of phenological events.
    "Determining bumble bee species' plant selection is important for retaining and promoting high quality plant resources that will help populations persist," the authors said.

    The plants bumble bees prefer

    The authors assessed the five most abundant bumble bee species' plant selection by comparing the plants they used to what was available. Although they captured bees on more than 100 plant species, just 14 of them were chosen the most.
    Each bumble bee species selected a different group of flowers, even though the bees were foraging across the same plots.
    "It's important to consider the availability of plants when determining what's selected for by bees," Cole said. "Often studies will use the proportion of captures on a plant species alone to determine which plants are most important to bees."
    The American bumblebee is at risk of extinction in Canada, scientists say