Interactive effects of abiotic environmental conditions and herbivory on an invasive annual vine
Classical biological control of non-native invasive plants offers great promise for invasive plant management. Introduced host-specific insect herbivores from a plant’s native range can suppress growth and reproduction of the invasive plant in its new range, reducing its ability to compete with native plants and dominate the landscape. However, both plants and insects are subject to varying abiotic environmental conditions that can affect their interaction. Our studies focused on the interaction between the stem-boring weevil Rhinoncomimus latipes and the invasive vine mile-a-minute weed, Persicaria perfoliata. Feeding damage by R. latipes has been shown to reduce P. perfoliata percent cover and biomass, and delay and reduce seed production. However, the impact in the field has varied from year to year. We conducted greenhouse studies examining the impact of the weevil on the plant under controlled moisture conditions, and environmental chamber studies at different temperatures to determine the lower developmental threshold and growing degree-day requirements for weevil development. Results were compared with long-term field monitoring studies.
In greenhouse trials, both water limitation and weevil herbivory reduced mile-a-minute reproduction and growth compared to well-watered plants. In environmental chambers, the lower developmental threshold for the weevil was estimated at 10.2 °C, and average time of development from egg to adult varied from 19 days at 30 °C to 39 days at 20 °C. In the field, intensively monitored sites had relatively high P. perfoliata cover and low R. latipes densities in 2009 compared to either 2008 or 2010. Summer temperatures were lower in 2009, allowing fewer R. latipes generations to develop that year compared to 2008 and 2010. Substantially higher spring rainfall probably also helped P. perfoliata develop more abundant cover in 2009 than in 2008 or 2010. Both temperature and moisture effects can help explain varying impacts of the weevil in different years with different weather conditions. This information may also help predict varying impacts of the weevil in different parts of the plant’s range, as both P. perfoliata and R. latipes continue to expand their geographic range in North America, and under changing climatic conditions.