About This Project

Pitcher’s thistle is a rare native plant that is found only one place in the world; the sand dunes of the Great Lakes. The invasion of a seed-eating weevil further threatens the plant's extinction. We will conduct a mark-recapture study to learn more about weevil dispersal and test the use of sticky, 3-D printed decoy flowers as a management strategy. This study has important implications for Pitcher's thistle conservation and invasive insect management.

Ask the Scientists

What is the context of this research?

Pitcher’s thistle (Cirsium pitcheri), is a federally-threatened native plant that is one of the only sources of nectar to pollinating insects along the sand dunes of Lake Michigan. Although facing many threats, this plant is also the victim of a biocontrol-gone-wrong story (Havens et al. 2012). The invasive Larinus carlinae weevils (formally L. planus) were initially distributed in the US to control weedy thistles. Sadly, they are not very good at stopping weedy thistles and readily attack native thistles (Louda and O'Brien 2002), including the rare and charismatic Pitcher's thistle. In early summer, the "evil weevils" chew holes in the unopened flower heads where they lay their eggs. The developing larva eat the developing seeds, preventing the plant population from growing.

What is the significance of this project?

Although the Larinus weevils have been in the US for several decades, they have only recently invaded Pitcher's thistle populations along Lake Michigan. The weevils have greatly increased the threat of extinction for the rare plant, but we are learning important information that we hope can be used to help manage the invasive weevil and conserve the plant, especially in places where the weevil hasn't arrived yet. Our previous research identified areas of the dunes that are more susceptible to weevil attack (Hakes et al. 2018). Weevils are attracted to thistles located at lower dune elevations and in cooler, grassy-areas. It's time to use that knowledge against them! The grassy areas of the dune where weevils are naturally prevalent are the perfect place to test our traps.

What are the goals of the project?

The goals of this project are to 1) better understand how weevils move, find, and select host plants in the dunes, and 2) test the efficacy of using decoy flowers as weevil traps. We know from earlier experiments that the grassy areas of the dunes are where weevils are most prevalent and that grasses may help them get to the host thistles. We don't know how often and how far weevils disperse from plant to plant. By giving each weevil a unique paint marking, we can survey how much they are moving in the dune community. For our second goal, we will place 3D printed decoy plants treated with tangle-foot in the grassy areas where weevils are dispersing. This will test whether visual cues of the host plant are enough to trap weevils. If effective, this management strategy can be amplified.