Hybrid forms of the Culex pipiens Complex ( Diptera : Culicidae ) : New records in

The Culex pipiens Complex is widely studied because of its medical and veterinary relevance as a vector of pathogens that cause various diseases to humans as well as animals (e. g., encephalitis arboviruses, filariasis, and avian malaria; Mitchell et al. 1985; Díaz et al. 2006; Vezzani et al. 2006). Members of this complex can be differentiated by certain ecophysiologic characteristics such as the production of the first egg raft without previously feeding on blood (autogeny), the ability to mate in small spaces (stenogamy), and the preference for open spaces to mate (eurygamy); molecular-genetic techniques (e. g., gene mapping by PCR); and morphometric indices (Vinogradova 2003; Vinogradova et al. 2007). Among the latter are the siphonal index (S. I.) and the DV/D ratio. The S. I. is the ratio between the length of the siphon, (measured as the distance from the base to the apex of the siphon, on the dorsal surface, excluding the spiracular apparatus), and the basal width of the siphon, (measured at right angles to the longitudinal axis of the siphon) (Brogdon, 1981, 1984). The DV/D ratio, as applied to the male genetalia, is the ratio of the distance between the ends of the dorsal and ventral arms of lateral plate of the phallosome on one side and the distance between the two dorsal arms (Barr, 1957). In Argentina, Culex pipens Complex is represented by: Culex (Culex) quinquefasciatus Say, Culex (Culex) pipiens Linnaeus, and hybrids between the two species. The range of its distribution, as well as of its hybrids, is not entirely clear. Culex quinquefasciatus occurs in the central and northern regions, whereas Cx. pipiens is found from central and southern Argentina (south of Santa Cruz Province) (Duret, 1953; Mitchell et al. 1984; Mitchell and Darsie, 1985). Therefore, distribution of both species overlaps in the central region (Mitchell et al. 1984; Brewer et al. 1987; Almirón et al. 1995; Diez et al. 2011). With respect to the hybrids, Brewer et al. (1987) recorded their presence in Quebracho Flojo Village, Córdoba capital city, and the city of Cruz del Eje, all in Córdoba Province, situated between Abstract: The present investigation revealed the existence of hybrids belonging to the Culex pipiens Complex in four localities of La Pampa Province, Argentina, thus expanding the distribution of the hybrid form south to the northeast of that province. The identification was based on characters of the male genitalia and the siphonal index of the fourth-instar larval exuviae. A summary of the geographical distribution of species of Culex pipiens complex in Argentina is also presented here. 1 Universidad Nacional de La Pampa, Facultad de Ciencias Exactas y Naturales. Avenida Uruguay 151, (L 6300 CLB) Santa Rosa, La Pampa, Argentina. 2 Centro de Estudios Parasitológicos y de Vectores (CEPAVE) CCT La Plata, CONICET UNLP Calle 2 No 584, (B1902CHX) La Plata, Argentina. * Corresponding author. E-mail: fddiez@gmail.com Fernando Diez 1*, Víctor Julián Breser 1, Estela Maris Quirán 1 and Gustavo Carlos Rossi 2 Hybrid forms of the Culex pipiens Complex (Diptera: Culicidae): New records in La Pampa Province, Argentina

Fernando Diez1* , Víctor Julián Breser 1 , Estela Maris Quirán 1 and Gustavo Carlos Rossi 2   Hybrid forms of the Culex pipiens Complex (Diptera: Culicidae): New records in La Pampa Province, Argentina latitudes 30° S and 32° S. In addition, Almirón et al. (1995) recorded hybrids in the city of Rosario, Santa Fé Province, latitude 36°13'37" S; and Morais et al. (2010) did it in La Plata, Buenos Aires Province at a latitude of 35° S. (Fig. 1) Culex quinquefasciatus (Carpintero and Leguizamón, 2004) and Cx.pipiens (Diez et al. 2011) were also recorded in La Pampa Province, although no hybrids were found there.The objectives of this study were: to assess the presence of hybrids of Culex pipiens and Culex quinquefasciatus in the northeastern section of La Pampa Province; and to clarify the distribution of species of Culex pipiens Complex in Argentina.
In each locality, we investigated two pneumatic-tire yards and the local cemetery.In the first area (Winifreda), 322 containers (glass, metal, plastic, and ceramic jars of from 0.5 to 2 liters) were surveyed, among which only 7 samples were positive.Larvae and pupae were taken from the containers and transported to the laboratory.Similar numbers of positive samples were taken from the other sampling sites to maintain a constant sampling volume along the entire experiment.From the several samples from used-tire warehouses, 5 were found positive as regards the presence of immature Culex pipiens Complex mosquitoes.
The immature mosquitoes were transported to the Biología de Invertebrados II laboratory at UNLPam.Larvae and pupae from each location were both kept in 1,500 ml containers, containing 750 ml of chlorine-free water at 25 ± 4 °C in a 14:10-h.light-dark photoperiod.Larvae were fed 200 mg commercial chicken food every 4 days up to the pupae stage.During this period, the fourth-instar larval exuviae were separated to assess the S. I. under a Kyowa stereoscopic microscopic at a 72X magnification.Once emerged, the adults were sugar-fed on raisins along three days.The distance between the ends of the dorsal and ventral arms of lateral plate of the phallosome on one side, and between the two dorsal arms were measured under a Nikon YS100 binocular microscope at a 100X magnification with the aid of an ocular micrometer.Both the siphons and the genitalia were placed on microscope slides immersed in a drop of 80% ethanol without cover slips in order to avoid distortions.Specimens with S. I. values of 4.30 or higher were identified as Cx.pipiens; those with values of 3.40 or lower were identified as Cx.quinquefasciatus; and those with S. I. values >3.41 but <4.29 were considered to be hybrids (Brogdon, 1981(Brogdon, , 1984)).Specimens with DV/D ratios of 0.20 or lower were identified as Cx.pipiens; those with ratio of 0.40 or higher as Cx.quinquefasciatus; and those with ratio >0.21 but <0.39 as hybrids (Barr, 1957).
A total of 845 Culex pipiens Complex larvae were collected, 368 of which were males and 477 females.All siphons of fourth-instar larval exuviae were measured and

Table 1 .
Presence of hybrids of Culex quinquefasciatus and Culex pipiens, in four localities of La Pampa Province.