The specificity of the specialisation of Phengaris Doherty, 1891 caterpillars to their host ants is still not fully understood. In this report, we summarize all available records of Phengaris in ant nests from the Czech Republic. P. alcon (Denis & Schiffermüller, 1775) was found exclusively in nests of Myrmica scabrinodis Nylander, 1846 at four sites, and one P. nausithous (Bergsträsser, 1779) caterpillar was found in a nest of M. scabrinodis. According to published records, P. nausithous may use M. scabrinodis at the edges of its range but should be adapted exclusively to M. rubra (Linnaeus, 1758) in the centre of its range. No records of P. arion (Linnaeus, 1758), P. teleius (Bergsträsser, 1779) and P. alcon populations feeding on Gentiana cruciata (Gentianaceae) (“P. rebeli”) are available from the Czech Republic.

Phengaris Doherty, 1891 (=Maculinea van Eecke, 1915) butterflies are among the most studied insects in Europe due to both their vulnerability and unique myrmecophilous life habits (Settele et al. 2005). Females lay eggs on the flowers of species-specific host plants, and hatched caterpillars feed on unripe seeds inside the flowers. After the first three instars, caterpillars leave their host plants and fall to the ground, where they are immediately adopted by ants of the genus Myrmica Latreille, 1804. Then, caterpillars feed on ant brood or mimic ant larvae and are fed directly by ant workers. They overwinter once or twice inside ant nests before they pupate (Chapman 1916; Settele et al. 2005).

The level of Phengaris specialisation on host ant species has been much discussed during the past few years. According to previous thinking, each species (or population) of Phengaris should be specialised to one species of Myrmica as their “primary host” and possibly one or several more species as “secondary host” ants (Thomas et al. 1989; Settele et al. 2005). The survival of caterpillars should be much higher in the nests of primary hosts than in the nests of secondary hosts. Caterpillars may be adopted by many ant species, but they die in nests of non-host ants. As more records of caterpillars in Myrmica nests have appeared, however, the intimacy of the Phengaris specialisation has become questioned (Pech et al. 2007). Today, the level of specialisation and character of the Phengaris-Myrmica host system is still not completely understood (Filz and Schmitt 2015) and new data are needed for future analyses.

Most Phengaris host specificity data were obtained in central and eastern Europe, especially in Poland and Hungary (Stankiewicz et al. 2005; Tartally et al. 2008; Tartally and Varga 2008; Witek et al. 2008; Sielezniew and Dziekańska 2009; Sielezniew and Stankiewicz-Fiedurek 2009). The use of this information is quite problematic for Phengaris populations in other parts of Europe, because the Phengaris host specificity shows geographical variability, at least in some cases (Als et al. 2002; Stankiewicz et al. 2005). For example, M. scabrinodis Nylander, 1846 is the most common host of P. alcon (Denis & Schiffermüller, 1775) in central Europe, but not used in development of caterpillars at all in Denmark (Als et al. 2002).

The area of the Czech Republic is very interesting from a biogeographical point of view as a result of quarternary history. The ranges of many closely related species from different taxa (originating from a common ancestor in refugees of southern Europe during the last glacial) meet in or close to the Czech Republic, e.g. snails (Horsák and Novák 2005), slow worms (Gvoždík et al. 2010), hedgehogs (Bolfíková and Hulva 2012), as well as ants (Seifert 1995; Schlick-Steiner et al. 2006) and butterflies (Konvička et al. 2008). Knowledge of the host specificity of Phengaris blues in the Czech Republic (as well as in Germany) will add a potentially interesting piece to the mosaic of the Phengaris-Myrmica system. We have tried to summarize all published records of Phengaris caterpillars in ant nests available from the Czech Republic and unpublished records from Czech lepidopterologists and other conservationists interested in Phengaris blues. Because there is only one paper dealing with Phengaris host specificity data from the Czech Republic (Witek et al. 2008) and we can not find anyone having unpublished records available, we have decided to publish data (however scarce) from our field research. Although our data are far from complete and exhaustive, we believe that even anecdotal records may contribute to the mosaic of our present knowledge about the geographical variation of Phengaris host specificity.

All searched sites of P. alcon (Placy, Mečichov, Jindřichovice, Nahošín) and P. nausithous (Bergsträsser, 1779) (Josefov) are wet meadows with Molinia caerulea L. (Moench) (Poaceae) as a dominant component. In Placy (central Bohemia, 49°40’N, 14°06’E), five plots (1×2m, all in the close vicinity of Gentiana pneumonanthe L., Gentianaceae) were searched. All nests in the plots were opened using a garden rake to collect a sample of ants and to check for the presence of Phengaris at the surface. In Jindřichovice (49°23’N 13°51’E) and Nahošín (49°21’N 13°50’E) (both south-western Bohemia), 10 whole nests from the vicinity of host plants (G. pneumonanthe or Sanguisorba officinalis L., Rosaceae) were dug out and searched through in the lab. In Mečichov (49°20’N, 13°47’E; south-western Bohemia), many ant nests were opened using a garden rake in 2000–2001, with nests checked in a 325 m² area independently of the position of host plants. This research was not aimed at studying the Phengaris host specificity and the numbers of infested ant nests were not recorded precisely; thus, these results are not useful for quantitative analysis. To obtain some basic quantitative data, 15 whole nests were dug out and searched in the same manner as in Jindřichovice and Nahošín. In Josefov (eastern Bohemia, 50°20’N, 15°55’E), a caterpillar was found incidentally during the investigation of two Myrmica nests, which were dug out and searched through in the lab to count ant workers and juveniles.

There are very few records of Phengaris caterpillar or pupae in Myrmica nests from the Czech Republic. In addition, there are as yet no records of P. arion (Linnaeus, 1758) or P. alcon populations feeding on Gentiana cruciata L. (Gentianaceae) (“P. rebeli”) (see Kudrna and Fric (2013) and Tartally et al. (2014) for a recent view on taxonomical status and biology of P. alcon and P. rebeli (Hirschke, 1904)).

Witek et al. (2008) published data from two localities of P. teleius (Bergsträsser, 1779) from the Czech Republic. M. scabrinodis was the only recorded host ant, but as P. teleius commonly develops in nests of many Myrmica species (Pech et al. 2007; Witek et al. 2008), these exclusive records from M. scabrinodis nests are clearly related to the low number of observations and other host ants cannot be ruled out.

Several records of P. alcon and one of P. nausithous were obtained by our field research (Table 1; Fig. 1). P. alcon used M. scabrinodis as a host at all four localities (Fig. 2). In addition to the data in Table 1, 260 nests of M. scabrinodis, 61 of M. ruginodis Nylander, 1846, four of M. vandeli Bondroit, 1920, three of M. rubra (Linnaeus, 1758) and in total 54 nests of non-Myrmica ants (Lasius niger (Linnaeus, 1758), L. platythorax Seifert, 1991, L. flavus (Fabricius, 1782), Formica fusca Linnaeus, 1758 and F. polyctena Förster, 1850) were opened in Mečichov in 2000–2001. We found many nests of M. scabrinodis infested by P. alcon, but no other ants hosting these caterpillars at this locality. Unfortunatelly, the presence of caterpillars in ant nests was not recorded precisely to allow quantitative analysis, but the observations correspond to the published data, because M. scabrinodis is the most common host of P. alcon in central Europe, although P. alcon is able to develop in the nests of many Myrmica ants (Pech et al. 2007; Witek et al. 2008; Sielezniew and Stankiewicz-Fiedurek 2009; Sielezniew et al. 2015).

Figure 1. 

Location of sites where records of caterpillars of P. alcon (triangles) and P. nausithous (circles) in ant nests are known in the Czech Republic.

Figure 2. 

Pupae of P. alcon in a M. scabrinodis nest. Locality Placy near Příbram in Central Bohemia, 1 July 2015. Photo: Ondřej Sedláček.

Interestingly, a single caterpillar of P. nausithous was found in a M. scabrinodis nest in Josefov (Fig. 3). P. nausithous is the Phengaris species with the lowest number of known Myrmica hosts (two species only). It usually parasitizes nests of Myrmica rubra (Thomas et al. 1989; Tartally and Varga 2005; Witek et al. 2008), and the only other known host species of P. nausithous is M. scabrinodis. However, there are very few such records, all of them from the southwestern or eastern edge of the European range of P. nausithous (Munguira and Martín 1999; Witek et al. 2008; Tartally et al. 2008, 2010). According to Jansen et al. (2012), P. nausithous may depend on M. rubra in the centre of its range, whereas populations at the edges of its range may use M. scabrinodis. The caterpillar was found in December, 3-4 months after the adoption by ants. Because Phengaris caterpillars can be adopted by many ants (including non-host species) (Thomas et al. 1989), but then later die in their nests, our finding may be such a case. However, this is contradicted by the data of Patricelli et al. (2010), who found that P. nausithous juveniles died in nests of non-host Myrmica ants within one month of adoption. Thus we suggest that it is legitimate to consider M. scabrinodis as a true host of this caterpillar.

Figure 3. 

The locality near Josefov, Eastern Bohemia, where the caterpillar of Phengaris nausithous was found in a nest of Myrmica scabrinodis. Photo: Pavel Pech.

The host specificity of P. nausithous and its relationship to host ants thus may be more complicated than previously thought. Our record in Josefov shifts the use of M. scabrinodis 200 kilometres closer to the heart of the European distribution of P. nausithous according to Wynhoff (1998). Unfortunately, there are almost no other data from this part of the P. nausithous distribution. It should be noted that P. nausithous is sometimes common at sites where M. rubra is absent or rare (Czech Republic - pers. observation; Netherlands - Jansen et al. 2012), and, if present, the infestation of M. rubra nests by P. nausithous is usually low (Tartally and Varga 2005; Witek et al. 2008). In such situations, it is unclear whether a rich population of P. nausithous can be supported. At the moment, the relationship of P. nausithous to Myrmica remains to be fully elucidated.

We are obliged to Kristýna Henebergová, Barbora Kupková, Milan Janda and Zdenka Křenová for help in the field and Marcin Sielezniew and an anonymous referee for valuable comments on a previous version of the paper. David Hardekopf improved the English of the paper and Jan Košnar made the map. The research was partially supported by the Ministry of Education, Youth and Sports of the Czech Republic, research project no. 2114/2014.