Status of Biological Control for Managing Invasive Arundo Donax in Coastal Floodplains
Tom Dudley1*, Adam Lambert1, K. Sheehy1, C. Braman1 & Z. Ozsoy2
1Marine Science Institute, University of California, Santa Barbara
2Biology, Colorado Mesa University
Giant reed (Arundo donax) is a dominant vegetation type in many low-gradient river systems from Texas to coastal California, often in association with Tamarix spp., where it has displaced native woodlands, promoted wildfire, altered channel geomorphology and offers poor habitat for wildlife. Conventional mechanical-chemical control can be effective, but costs are prohibitive and collateral damage high, so biocontrol has been promoted for improved riparian restoration. In concert with USDA-ARS researchers (Drs. Patrick Moran and Scott Portman) we have initiated efforts to release two APHIS-approved Mediterranean agents into California, a stem-boring wasp, Tetramesa romana, and a rhizome-tapping armored scale, Rhizaspidiotus donacis. However, releases are complicated by the finding of both insects already established in the state, and genetic tests are being conducted to determine how closely related these unintentionally introduced insects are to the imported material. The wasp has much less impact to target plants than those intentionally released in Texas, but the low establishment and impact of T. romana released by USDA in northern California suggests that differences are owing to environmental conditions rather than genotypic traits. The pre-existing R. donacis also performs differently at our sites than is reported from Texas, further indicating a need to compare efficacy of both populations of each insect before widespread releases of European forms are undertaken. Future work should also investigate the potential for host-specific pathogens to suppress Arundo growth and facilitate recovery of native riparian vegetation.