Plant associations occur when host selection of a focal plant is reduced or increased by the presence of another plant species. Larinus planus is an invasive weevil whose larvae feed in the flower heads of native and federally threatened Pitcher’s thistle (Cirsium pitcheri). Studies have linked the presence of neighboring plants to increased host selection of Pitcher’s thistle by the weevil, but the factors contributing to host selection remain unknown. In our study, we determined if there were differences among abiotic factors, host selection and weevil behavior at Pitcher’s thistles surrounded by beach grass, sand and at high elevation. We used HOBO sensors to assess temperature and light intensity at surface level of individual Pitcher’s thistles. To determine the effects of wind, we recorded the average wind speed using a Kestrel at high and low elevations during a 30-minute time interval. We assessed the influence of abiotic conditions on weevil behavior by observing individual weevils and noting abiotic conditions during the observation period. Our results indicate that there are differences in abiotic factors among thistle habitats, with lower average temperatures and light intensities found at Pitcher’s thistles neighboring other plants and lower average winds at low elevations. The probability of a weevil reaching a Pitcher’s thistle was negatively correlated with temperature. Our results suggest that neighboring plants influence the abiotic factors surrounding individual Pitcher’s thistles.
Level of Honors
magna cum laude
Paniagua Montoya, Monica, "Abiotic conditions of rare Pitcher's thistle attract selection by an invasive weevil" (2017). Lawrence University Honors Projects. 106.