Ant parasitic fungi

The minute mistery: Rickia wasmannii Cavara, 1899

The genus Rickia it is one of the largest known genera within the Laboulbeniales and it contains around 145 species (Weir, 1998). Tavares (1985) reported 122 species and one variety. In the latest monographic work dealing with the genus Rickia, where 17 species from Sulawesi are reported, 5 of them new. Weir (1998) refers to approximately 145 species. According to the MycoBank databases (http://www.mycobank.org), the genus included 151 species, excluding varieties and duplicities. This genus is mainly tropical, with 84% of the species living in such environments (Weir and Hammond, 1997). Over 17 species were reported in Europe (Majewski, 1994 and De Kesel et al., 2013). The host range of Rickia species encompasses distantly related arthropods such as mites (Acarina), millipedes (Diplopoda), mole crickets (Orthoptera), ants (Hymenoptera) and various beetles (Coleoptera) (Weir, 1998).

The fungus Rickia wasmannii was understudied for a long time but in recent years more reports about its distribution and host ant usage have been published, and these have shown R. wasmannii to be the most widely distributed of the four ant-parasitizing Laboulbeniales species in Europe (Fig. 3., Espadaler and Santamaría, 2012; Haelewaters, 2012, Csata et al., 2013, 2014; Haelewaters et. al., 2015; Santamaría and Espadaler, 2015; Báthori et al., 2014, 2015). Rickia wasmannii was originally described from Germany by Cavara (1899) on Myrmica rubra (Linnaeus), collected in Linz on the Rhine by the renowned myrmecologist Wasmann during 1897 (Weir, 1998).

Head of Myrmica scabrinodis worker covered by Rickia wasmannii thalli (SEM photo by Ciprian Mihali)

Head of Myrmica scabrinodis worker covered by Rickia wasmannii thalli (SEM photo by Ciprian Mihali)

It has been reported from England, France, Germany, Luxembourg, The Netherlands, Switzerland, Poland, Italy, Austria, Slovenia, the Czech Republic, Slovakia, Hungary, Romania and Bulgaria, parasitizing eight species of the genus Myrmica Latreille 1804 (Hymenoptera: Formicidae), such as: Myrmica curvithorax Bondroit, 1920 as senior synomym of M. slovaca Sadil, 1952, M. scabrinodis Nylander, 1846 (Fig. 3.); M. specioides Bondroit, 1918; M. vandeli Bondroit, 1920; M. rubra (Linnaeus, 1758); M. sabuleti Meinert, 1861; M. gallienii Bondroit, 1920 and M. ruginodis Nylander, 1846 (Tartally et al., 2007; Lapeva-Gjonova and Santamaría, 2011; Bezdĕčkova and Bezdĕčka, 2011; Espadaler and Santamaría, 2012; Haelewaters, 2012; Csata et al., 2013; Santamaría and Espadaler, 2014).

The thallus of Rickia wasmannii consists of a multiseriate receptacle which is only one layer of cells thick, while only sexual stages are known (Haelewaters, 2012). The fungal thalli penetrate the outer layer of the cuticle, and appear on the surface of the hosts as clubbed setae-like structures under the stereoscope (Fig. 4, 5). This makes the infected host easy to recognize for the myrmecologist, as highly infected ants appear unusually hairy (Fig. 3).

Thallus of Rickia wasmannii on the gaster of Myrmica scabrinodis (SEM photo by Ciprian Mihali)

Thallus of Rickia wasmannii on the gaster of Myrmica scabrinodis (SEM photo by Ciprian Mihali)

Little is known about the effect of the Laboulbeniales fungi on their hosts, and while the fungi are parasitic and penetrate to the hemocoel of the host, they have been usually regarded as neutral (see Tartally et al., 2007; García et al., 2010; Lapeva-Gjonova and Santamaría, 2011; Bezděčka and Bezděčková, 2011; Espadaler and Santamaría, 2012).

In Romania, it was first reported by Tartally et al. (2007) on Myrmica scabrinodis from two localities: Fânaţele Clujului (Cluj-Napoca) and Luna de Jos, all in Cluj County, Transylvania, central Romania. Since then, ten more locations were found (Fig. 1): between Colţeşti and Izvoarele in Alba County, near Chinteni, near Săvădisla, between Tureni and Miceşti and near Vişea, near Borșa Cătun, and near Dârja in Cluj County, near Sighişoara in Mureş county, in the Vârghiş Gorge near Vârghiş in Covasna County, and near Jigodin-Băi in Harghita County.

In the majority of all known populations, M. scabrinodis is the only or the primary host, with the exception of the population in Tureni, where it was found mainly on M. rubra along M. scabrinodis. At Vişea it was found both on M. scabrinodis and M. curvithorax, near Colţeşti on M. gallienii  and M. rubra as well, while near Sighișoara on M. ruginodis. Myrmica ruginodis is a new host species for R. wasmannii so far (Espadaler and Santamaría, 2012).

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