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

Author
item Goolsby, John
item Moran, Patrick
item RACELIS, ALEXIS - The University Of Texas-Pan American
item SUMMY, KENNETH - The University Of Texas-Pan American
item MARTINEZ-JIMENEZ, MARICELA - Instituto Mexicano De Tecnologia Del Aguas
item LACEWELL, RONALD - Texas A&M University
item Perez De Leon, Adalberto - Beto
item KIRK, ALAN - Former ARS Employee

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2014
Publication Date: 10/23/2015
Citation: Goolsby, J., Moran, P.J., Racelis, A.E., Summy, K.R., Martinez-Jimenez, M., Lacewell, R.D., Perez De Leon, A.A., Kirk, A.A. 2015. Impact of the biological control agent, Tetramesa romana (Hymenoptera: Eurytomidae) on Arundo donax (Poaceae: Arundinoideae) along the Rio Grande River in Texas. Biocontrol Science and Technology. 26(1):47-60.

Interpretive Summary: The arundo wasp, Tetramesa romana, is a plant-feeding, gall-making insect biological control agent for the invasive weed - Arundo donax, also known as giant reed or carrizo cane. This weed, which is native to Spain, grows along the banks of the Rio Grande (and other rivers in the southwestern U.S.), and causes serious ecological impacts by displacing native vegetation, enhances the survival of cattle fever ticks in the permanent quarantine zone, interferes with law enforcement activities along the international border and competes for scarce water resources in an arid region already experiencing extended drought and potential changes from climate change. The arundo wasp was released in 2009 and is causing visible and measurable damage to giant reed. A comparison was made of stands of the plant at various locations along the Rio Grande in 2007 before release of the wasp and in 2014. Since release, the wasp has reduced above ground growth of the plant by 22% along the 558 river miles between Del Rio and and Brownsville, TX. This reduction is estimated to be saving 4.4 million dollars in agricultural water per year. A second insect, the arundo scale was released in 2012 and a third, the arundo leafminer is proposed release in the fall of 2015. The combination of these insects should reduce the most serious effects of this invasive weed and allow for the re-growth of the native trees and shrubs along the Rio Grande.

Technical Abstract: Five years post release of 1.2 million arundo wasps, Tetramesa romana, into the riparian habitats of the lower Rio Grande River; changes in the health the invasive weed, Arundo donax, giant reed have been documented. These changes in plant attributes are fairly consistent along the 558 river miles between Del Rio and Brownsville, TX and support the hypothesis that the arundo wasp has had a significant impact as biological control agent. Plant attributes were measured in ten quadrats at each of ten field sites in 2007 prior to release and again at the same sites 5 years post-release of T. romana in 2014. Above ground biomass of A. donax decreased on average by 22% across the ten sites. This change in biomass was negatively correlated to the total number of T. romana exit holes per site in 2014 of main and lateral shoots (r = -0.67, P = 0.0341). Live shoot density per m2 in 2014 was negatively correlated total exit holes (r = -0.74, P = 0.013). An increase in dead shoot density and decline in the proportion of live shoots from 2007 to 2014 suggests that T. romana is reducing recruitment of live shoots. Galled main and lateral shoots were more likely to be dead than ungalled. 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 in the riparian zone. 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.