Bumble bees for Paintbrush plants for Checkerspots

To create a good home for future populations of Taylor’s checkerspot butterfly, CNLM works hard to establish patches of tasty, nutritious host plants for checkerspot larvae to eat.  Two of the key native host plants are Castilleja species: at some sites we plant native Castilleja hispida, the harsh paintbrush; at others, federally listed Castilleja levisecta, the golden paintbrush. We have had great success in planting these species, yet we would like to know how well they are integrating into the prairie ecosystem and whether they will persist over the years. One key question is whether they are getting visited by our prairie pollinators.

We explored plant-pollinator networks—the web of interactions between all the plants and all the pollinators—at six sites in 2017. The sites ranged from pre-restoration to highly-restored prairie. We observed every flowering species at each site over the course of the season, and identified every insect that arrived to visit a flower. Then we used the data to create interaction webs, and explored the relationships of the two Castilleja species in the interaction webs.

We found some exciting things!  First of all, the interaction webs grew more complex in sites where restoration had progressed longer. This was not entirely unexpected, but it is good to have a signal that restoring plants is having a positive effect on the insects that depend on those plants. Second, we found that harsh paintbrush received far fewer visits from pollinators than golden paintbrush did, which might be important if it means that harsh paintbrush is setting less seed overall. Finally, bumble bees may be playing crucial roles for paintbrush pollination, making it important to keep an eye on the welfare of our bumble bees.

Preliminary pollination network from Glacial Heritage. The black bars on the bottom show plant species, with the width of the bar proportional to the number of times we saw that species receive pollinator visits. The top bars represent visiting insects (with morphospecies names). Red=bees, tan=flies, blue=wasps, gray=beetles, butterflies, moths, and true bugs.