Worldwide, syrphids (Diptera: Syrphidae) play important ecological roles in nature. Adults are usually conspicuous flies that feed on pollen and nectar from a wide range of plants in numerous habitats (Rotheray and Gilbert, 2011). In Europe, syrphids are one of the better studied Diptera families. However, the taxonomy of certain groups is still provisional and uncertain, such as the genus Chrysotoxum Meigen, 1803 (Speight, 2013).
Chrysotoxum species are present in all bio-geographic regions except for Australasia. In the Palaearctic region 71 species are recorded, 24 of which are present in Europe (Vockeroth, 1969; Violovitsh, 1974; Peck, 1988; Nedeljković et al., 2013). These wasp-mimics can be separated from other syrphid genera by the yellow and black body colouration (yellow maculae in thoracic pleura and yellow fasciae in abdominal terga), the very long antenna and the convex, margined abdomen (Thompson and Rotheray, 1998). Chrysotoxum adults are found in many habitat types (Speight, 2013) and their poorly known larvae are associated with ants and/or root aphids (Rotheray, 1994).
The taxonomy of certain Chrysotoxum species has proven difficult due to subtle morphological differences (Nedeljković et al., 2013) and high levels of intra-specific variability (Sang-Wook and Ho-Yeon, 2013). In these circumstances, integrative taxonomy is useful for testing species concepts. Integrative taxonomy is a multidisciplinary approach to taxonomy that aims to delimit the units of life’s diversity from different and complementary perspectives (e.g. comparative morphology, population genetics, ecology, behaviour) (Dayrat, 2005). Many species have been described among syrphids using an integrated approach (e.g. Marcos-García et al., 2011; Radenković et al., 2011; Skevington and Thompson, 2012; Locke and Skevington, 2013; Vujić et al., 2013; Haarto and Ståhls, 2014). To find genetic differences between similar species, analyses of both mitochondrial (e.g. COI) and nuclear (e.g. ITS2) genes have been used (e.g. Masetti et al., 2006; Vujić et al., 2012, 2013). In other Diptera families such as Drosophilidae wing shape is highly dependent on genetic inheritance and therefore minimally affected by temperature (Birdsall et al., 2000), altitude, and season (Bitner-Mathé and Klaczko, 1999). Wing morphometry has been used in integrative taxonomic studies of syrphids (e.g. Ludoški et al., 2008; Francuski et al., 2009, 2011; Vujić et al., 2013; Nedeljković et al., 2013). Male-genitalia morphometry has also been used (Nedeljković et al., 2013). Ecology plays an important role in diversification processes and ecological analyses have proven useful in supporting species concepts (Bond and Stockman, 2008; Nosil, Harmon and Seehausen, 2009; Wooten and Gibbs, 2012; Zhu et al., 2013). Funk et al. (2006) reported a highly significant positive association between ecological divergence and reproductive isolation across taxa. Although ecological analyses have not been used in integrative taxonomy of Syrphidae, unpublished data suggest they could be important (Ačanski J, Miličić M, Likov L, Radenković S, Vujić A, unpubl. data).
A preliminary examination of named specimens of Chrysotoxum vernale Loew, 1841 resulted in the identification of two different morphotypes according to the colour of long pile on thoracic scutum of males: yellow (morphotype A) and black (morphotype B) (Nedeljković, 2011). In addition, a new Chrysotoxum taxon sharing with morphotypes A and B an antenna with basoflagellomere shorter than scape and pedicel together and abdominal terga with yellow fasciae not reaching the lateral margins was recognized. The main objective of the present study is to test using an integrated approach, whether these morphotypes correspond to different species.