Impact of the biological control agent Tetramesa romana (Hymenoptera: Eurytomidae) on Arundo donax (Poaceae: Arundinoideae) along the Rio Grande River in Texas

ABSTRACT

Five years post-release of the arundo gall wasp, Tetramesa romana, into the riparian habitats of the lower Rio Grande River, changes in the health of the invasive weed, Arundo donax, or giant reed, have been documented. These changes in plant attributes are fairly consistent along the study area of 558 river miles between Del Rio and Brownsville, TX, and support the hypothesis that the arundo wasp has had a significant impact as a biological control agent. Plant attributes were measured prior to release in 10 quadrats at each of 10 field sites in 2007, and measured again at the same undisturbed sites, 5 years after the release of T. romana, in 2014. Above ground biomass of A. donax decreased on average by 22% across the 10 sites. This decline in biomass was negatively correlated to increased total numbers of T. romana exit holes in main and lateral shoots per site in 2014 compared to 2007. Changes in biomass, live shoot density and shoot lengths, especially the positive effect of galling on main and lateral shoot mortality, appear to be leading to a consistent decline of A. donax. Economically, this reduction in A. donax biomass is estimated to be saving 4.4 million dollars per year in agricultural water. Additional impacts are expected as populations of the wasp increase and as other biological control agents such as the arundo scale, Rhizaspidiotus donacis, become more widespread.

KEYWORDS:

• Biological control
• giant reed
• carrizo cane
• invasive weeds
• gall-forming wasp
• pathogenic landscape

Acknowledgements

The authors wish to thank Emmett Kunz, Ann Vacek, and Crystal Salinas (University of Texas – Pan American, Edinburg, TX), Matthew Rector, Madeline Marshall (Texas A&M University Agrilife Research, Weslaco, TX), Amede Rubio (Texas A&M International, Laredo, TX) and Reyes Garcia, III (USDA-ARS, Cattle Fever Tick Research Laboratory, Edinburg, TX) for the field collection and processing of the A. donax samples. We wish to thank Quentin Paynter (Manaaki Whenua Landcare Research, Auckland, New Zealand), John Adamczyk (USDA-ARS, Poplarville, MS), and Julia Goolsby (Stanford University, Palo Alto, CA), Roy Van Driesche (University of Massachusetts, Amherst, MA) and an anonymous reviewer for helpful edits of the manuscript. This article reports the results of research only. Mention of a commercial or proprietary product in this article does not constitute an endorsement by the US Department of Agriculture. The USDA is an equal opportunity provider and employer.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Funds for research support were provided by the Department of Homeland Security, Customs and Border Protection and the Lower Rio Grande Valley Development Council.