RHINELLA MAJOR MULLER & HELMICH, 1936 (ANURA: BUFONIDAE): NEW HOST OF AMBLYOMMA ARGENTINAE NEUMANN, 1905 (

.— During herpetofauna monitoring in Misión Nueva Pompeya locality, Chaco province, Argentina, an adult individual of the toad Rhinella major was captured. We examined the specimen and found a tick attached to the ventral surface of its body. The tick was identified as a nymph of Amblyomma argentinae , an ectoparasite considered specific to reptiles. This finding is the first record of this parasite-host association

Currently, the genus Rhinella includes 92 species distributed in the Neotropical region (Pereyra et al., 2021), of which 18 are present in Argentina (Vaira et al., 2012). Rhinella major Müller & Helmich, 1936 occurs in the Chaco region, Argentina, Bolivia and Paraguay, and in open formations along the rivers Beni, Madeira, Amazonas, Tapajós, and Xingú, and in the Amapá state, Brazil (Narvaez & Rodrigues, 2009). Its distribution in Argentina includes the provinces of Chaco, Corrientes, Formosa, Jujuy, Salta, Santiago del Estero, and Santa Fe. This toad is categorized as a non-threatened species (Vaira et al., 2012). It is moderately sized, insectivorous and inhabits grasslands near water bodies (Zaracho et al., 2011).
The genus Amblyomma comprises a group of hard ticks distributed widely across Neotropical and Afrotropical regions (Nava et al., 2017). Amblyomma contains 136 species, 25 of which have been recorded in Argentina (Guglielmone et al., 2021). Amblyomma argentinae Neumann, 1905 only has been reported in some Argentinean provinces, in the domain and province of Chaco with predominance in the Chaco and Serrano districts, and the province of Monte (Guglielmone & Nava, 2006;Guglielmone et al., 2021). This tick parasitizes a few species of turtles, lizards, snakes, and on single species of the Amphibia Class, the toad Rhinella sp. belonging to the family Bufonidae (see Guglielmone et al., 2021;Ruiz García et al., 2023). Herein, we report the first record of ectoparasitism of R. major by the tick A. argentinae in the Dry Chaco of Argentina.
On February 25, 2013, during a reptilian and amphibian survey in Misión Nueva Pompeya locality (24.9388°S, 61.4908°W, 158 m s.n.m.), General Güemes Department, Chaco province, Argentina, an adult male granulated toad R. major was collected by JARG and JAC (70.93 mm SVL; Fig. 1A). According to Morello et al. (2012), this locality belongs to Dry Chaco Ecoregion (Semiarid Chaco Subregion), complex Bermejito-Teuco-Bermejo. In this complex, the mean annual rainfall varies between 800 mm to the East and 600 mm to the West, concentrated in summer.
Annual mean temperatures varies between 21 °C to the East and 23 °C to the West.
We examined this specimen and found one tick attached to the ventral surface of the toad's body (Fig. 1B). The tick   The tick was identified as a nymph of A. argentinae (Fig. 1C  and 1D) according to Martins et al. (2014) and Nava et al. (2017). The characterisitc morphological structures used to identify this immature stage are the presence of the coxa II with only one spur and the scutum with deep punctations evenly distributed, larger and deeper laterally. The length and breadth of the scutum are: 0.71 mm and 1.02 mm, respectively. The main host of the A. argentinae is the Chaco tortoise Chelonoidis chilensis, with which its shares the distribution range and its abundance probably reflects the population dynamics of its principal host (Guglielmone et al., 2001;Nava et al., 2017).
Recent records mention the importance of lizards and snakes as the natural host of A. argentinae (Debárbora et al., 2015;Ruiz García et al., 2023). In Brazil, R. major is a common and relevant host of A. dissimile and A. rotundatum (Guglielmone & Nava, 2010;Calcavante Torres et al., 2018;Alves Coêlho, et al., 2019;Pedroso-Santos et al., 2020). However, although R. major is a frequently recorded species in the dry Chaco of the Chaco province, we do not know the role of this species on the populations of A. argentinae due to the little ecological information regarding this tick. In this sense, Guglielmone et al. (2001) mention that it is unclear whether amphibians have the potential to contribute to the maintenance of A. argentinae populations or only represent spillover onto ecologically associated hosts.
Although the majority of records of A. argentinae are associated with reptiles, in Neotropical hard ticks strict host specificity is not common (Nava & Guglielmone, 2013). Five species (33%) of A. argentinae hosts are under some degree of threat (Table 1), therefore, athough this report is based on an occasional finding, it is necessary to increase sampling efforts in the study area to obtain more ecological information on these association, and to update the hosts of this species.
Finally, our study reports for the first time R. major parasitized by A. argentinae. Moreover, it represent the second record of an amphibian as a host for this specie and extends the number of hosts up to 16 species (Table 1).