Introduction

Species of Tamarix (Caryophyallales: Tamaricaceae) are native of Eurasia and Africa and, due to their extraordinary biological features and adaptive capabilities (Fornasari 2004), have been introduced and established in 44 countries throughout the world.

At least four species of Tamarix (T. gallica, T. ramosissima, T. chinensis and T. parviflora) and their hybrids occur in Argentina (Gaskin and Schaal 2003; Natale et al. 2008). They were introduced to cover human necessities, mostly as windbreaks, to fix dunes, to control soil erosion, to supply shade, and in some desert places tamarisks are the lone surviving woody plants (León 2006).

However, tamarisk is now an alien plant that invaded the Pampean grasslands, mostly in coastal dunes or in riparian habitats, where it is more invasive, spreading over natural or semi-natural ecosystems (Zalba and Villamil 2002). In addition, tamarisk became a noxious weed in Llancanelo and Guanacache lagoons, both protected RAMSAR sites in Cuyo region, because its invasiveness produces soil salinization, water obstructions, and habitat modifications altering the riparian/wetland trophic structure (Sosa 2003). Consequences of tamarisk's invasiveness, such as water uptake and low diversity of dependent wildlife, have made it the target of classical biological control in the United States (Fornasari 1997, 2004).

Few insects are cited as affecting Tamarix spp. in Argentina: Ceroplastes sp., C. formicarius Hempel and Coccus hesperidum (L.) (Hem: Coccidae), Automeris aspersa (Felder) (Lep: Saturniidae), Oiketicus platensis Berg (Lep: Psychidae), Bostrichopsis uncinata Germ. (Col: Bostrichidae), and Praxithea deroudei (Chabrillac) (Col: Cerambicidae)(Cordo et al. 2004).

Methods and Materials

The geographic range of wild populations of Tamarix spp. cover most of Argentina, except the northeast (Natale et al. 2008). Seven out of 12 provinces where Tamarix spp occurs were surveyed. All the specimens were collected using entomological nets and manual aspirators. Specific identification was made using the keys provided by Oman (1936) and Linnavuori (1959), using both external and male genitalia's characters. Voucher specimens of O. stactogalus resulting from this study are deposited in the collections of the Museo de Ciencias Naturales de La Plata, Buenos Aires (MLPA) and Fundación e Instituto Miguel Lillo at San Miguel de Tucumán (IMLA), Argentina.

Results

Gonatocerus tuberculifemur Ogloblin (Hym: Mymaridae) is an egg parasitoid candidate for the control of Homalodisca vitripennis (Hem: Cicadellidae) in the United States (Jones et al. 2005). During the process of selecting leafhopper species for the study of their host range, abundant populations of a small leafhopper were found on Tamarix sp. in several sites in the Pampas and Monte provinces (Neotropical region, Chacoan subregion), and central and subandean patagonia provinces (Andean region, patagonian subregion) (sensu Morrone 2001); it was identified as the Holartic species Opsius stactogalus Fieber, 1866 (Hemiptera: Cicadellidae) known as the “Tamarix leafhopper”.

Opsius stactogalus (Deltocephalinae: Opsiini) is a leafhopper native to Europe and is strongly associated with the shrubby tree tamarisk (Wiesenborn 2001, 2002). The distribution is primarily Paleartic, but now nearly cosmopolitan, and always associated with tamarisk. Linnavouri & De Long (1977) found this species associated with Casuarina sp. in Chile. This species was previously mentioned by Metcalf (1967) for “Argentina” without locality or region reference, but the known distribution that was published by several authors subsequent to the Metcalf catalogue (Linnavuori 1959; Linnavouri and De Long 1977; Evans 1977; Oman et al. 1990; Zanol 2006) did not mention Argentina. The Tamarix leafhopper is a sap-feeder, and the aggregate feeding imposed by their populations can reduce tamarisk's growth (Liesner 1971, as cited by Wiesenborn 2002). Given the plant's pervasiveness and its undesirable qualities, new distributional data were obtained.

Discussion

Opsius stactogalus was found in all provinces sampled, except Córdoba (National Road n°7 km 526, near Gral. Levalle), in 12 out of the 13 sites surveyed. In all sites O. stactogalus was very abundant, however damage produced by this leafhopper on the sampled plants was not observed. Therefore, the potential usefulness of this hopper as a biocontrol agent for the invasive tamarisk populations established in Argentina is doubtful. Opsius stactogalus was also recorded in the United States of America, and again it did not cause significant damage to Tamarix spp. (De Loach 2001).

These findings encourage exploration for possible natural enemies of O. stactogalus, either natives of Argentina or others that arrived with this leafhopper, in order to better understand the community history of tamarisk in Argentina.