Densities of the Arundo Wasp, Tetramesa Romana (Hymenoptera: Eurytomidae) across its native range in Mediterranean Europe and introduced ranges in North America and Africa

Authors: MADELINE, MARSHALL - University Of Texas Rio Grande Valley; Goolsby, John; VACEK, ANN - University Of Texas Rio Grande Valley; KIRK, ALAN - University Of Montpellier; Moran, Patrick; CORTES, ELENA - University Of Spain; CRISTOFARO, MASSIMO - Bbca-Onlus, Italy; BOWNES, ANGELA - University Of South Africa; MASTORAS, ACHILLEAS - US Department Of State; KASHEFI, JAVID - US Department Of State

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2018
Publication Date: 7/3/2018
Citation: Madeline, M., Goolsby, J., Vacek, A.T., Kirk, A., Moran, P.J., Cortes, E., Cristofaro, M., Bownes, A., Mastoras, A., Kashefi, J. 2018. Densities of the Arundo Wasp, Tetramesa Romana (Hymenoptera: Eurytomidae) across its native range in Mediterranean Europe and introduced ranges in North America and Africa. Biocontrol Science and Technology. 28(8):772-785.

Interpretive Summary: Arundo donax L., also known as giant reed and carrizo cane, is native to Mediterranean Europe. It has become naturalized and invasive in many tropical, subtropical, and warm-temperate regions of the world. Arundo donax was introduced into North America from Mediterranean Spain in the early 1500s by colonists for use as roof thatching and quickly became naturalized. It is now found throughout the southern half of the United States from Maryland to California, but is most invasive in the southwestern United States and northern Mexico. Arundo donax is an extremely invasive weed of riparian habitat, drainage ditches and irrigation canals of the Rio Grande River Basin of Texas and Mexico (RGB). Arundo donax has historically dominated these habitats where it competes for scarce water resources and reduces riparian biodiversity. Arundo donax also facilitates the invasion of cattle fever ticks from Mexico into Texas, and impedes law enforcement activities along the international border. Biological control of Arundo donax a.k.a carrizo cane with insects may be the best long-term option for managing this highly invasive weed. A bi-national biological control program was initiated in 2009. Two specialist, insect biological control agents from the native range of Arundo donax in Spain, the arundo wasp, Tetramesa romana and the arundo scale, Rhizaspidiotus donacis have been released and established in Texas and Mexico, as well as in California. A third specialist insect, the arundo leafminer, Lasioptera donacis was permitted in 2017 and released in Texas. The attack by this combination of beneficial insects stimulates regrowth of native riverine plants. Transition of the riverine environment back to native vegetation conserves water, reduces risk of cattle fever tick invasion, and increases visibility of the international border for law enforcement. This paper compares the population levels of the arundo wasp in Texas with several locations in Mediterranean Europe where it is native. Population levels are estimated based on the tiny exit holes left in the Arundo donax cane after the wasp has completed its life cycle and chewed its way out. Population levels are up to 39 times higher in Texas, along the Rio Grande as compared to Europe. We present evidence that this difference is due to a more favorable climate in Texas as compared to Europe. The total daily accumulated heat units for one year in Texas are are 4500 to 5500 as compared to 2000 to 3000 in Europe. In addition, very few specialized parasitic insects attack the wasp in Texas as compared to Europe. In summary, favorable weather conditions and reduced parasitism in Texas along the Rio Grande, as compared to the native range, allows the arundo wasp to reach higher population levels and cause considerable damage to Arundo donax.

Technical Abstract: Tetramesa romana, the arundo wasp is a biological control agent of the giant reed, Arundo donax (Poaceae: Arundinoideae), which is an invasive weed in the riparian habitats of the Rio Grande Basin of Texas, the southwestern USA and northern Mexico. Field studies were conducted in the native range of T. romana in Mediterranean Europe and in the introduced ranges of Texas, California, and South Africa to compare densities of the wasp. We used timed counts of T. romana exit holes as a measure of population density across all sites. Exit holes are made by adult wasps as they complete their life cycle and chew out of A. donax galls. Tetramesa romana galls were collected at field sites and held in the laboratory for emergence of wasps and parasitoids to calculate percentage parasitism. Population densities and percentage parasitism levels for 2017 were compared to meteorological variables (average temperature, precipitation, and heat units). In the introduced ranges of Texas (intentional) and South Africa (adventive), T. romana population densities were 39 and 10-fold higher than in the native range, respectively. Percentage parasitism of T. romana in Texas and in the native range of Thessaloniki, Greece were 2.0% and 34.3%, respectively. Annual heat unit accumulation was 1.3 to 2.7-fold higher at Texas sites than at other introduced or native sites, and heat units were positively associated with exit hole counts at all sites. Annual precipitation was 2-fold higher at Texas and South African sites than in California and the native range sites. In summary, we found that favorable weather conditions and reduced parasitism of T. romana in Texas along the Rio Grande, as compared to the native range, has allowed the arundo wasp to reach higher population levels over time and cause significant damage to A. donax.