Andricus Hartig 1840

Andricus Hartig, 1840

The concepts of the gallwasp genera Andricus Hartig, 1840 and Callirhytis Foerster, 1869 are still somewhat chaotic, especially for Nearctic Callirhytis. According to Weld (1951, 1952a) species that have a basal lobe on their tarsal claws (toothed tarsal claw) belong to Andricus, while species without a basal lobe on the tarsal claws (tarsal claw simple) have been placed in Callirhytis. Nieves-Aldrey (1992), in his revision of the European Callirhytis species, showed that the sexual and asexual generations of different Callirhytis species vary in the presence or absence of toothed tarsal claws, and hence that this character cannot be used to distinguish these genera. Originally Callirhytis was erected for the European species by Foerster (1869) and the main generic diagnostic characters he proposed were the transversely striate mesoscutum and the presence of the malar sulcus. Weld (1922a,b, 1926, 1952a, 1959) included many species in Callirhytis and established particular species groups, but neglected the diagnostic characters of Callirhytis given by Foerster (1869). As a result, the Nearctic Callirhytis became a polyphyletic group, as has been demonstrated with multiple datasets (Nylander 2004, Liljeblad et al. 2008, Ronquist et al. 2015). Many North American species assigned to Callirhytis (Weld 1951, 1952a, Burks 1979) have already been transferred to the newly established genera Zapatella, Melikaiella and Kokkocynips (Nieves-Aldrey et al. 2021, Pujade-Villar et al. 2012a, 2014a). The tarsal claw character is equally confusing in Andricus. In some Andricus species, the male of the sexual generation has tarsal claws without a basal lobe, while in the females the basal lobe on the tarsal claws is present, for example, in the Western Palaearctic A. quercusramuli (Linnaeus, 1761) and the Eastern Palaearctic A. mairei (Kieffer, 1906) (Pujade-Villar et al. 2020b). Therefore, in our interpretation of Andricus and Callirhytis we have used other characters and ignored the presence/absence of the basal lobe on the tarsal claws. As a result, all of the relevant new species described herein have been placed in Andricus, regardless of this character. We also note that the presence/absence of a basal lobe on the tarsal claws remains a stable and important character at the species level.

Burks (1979), in accordance with Weld’s (1951) concept of the presence (Andricus) or absence (Callirhytis) of a basal lobe on tarsal claws, assigned 88 species to Andricus. Dailey & Sprenger (1973a) returned one species into Andricus, where it had originally been described but subsequently moved from. Melika & Abrahamson (2002) moved multiple species in and out of Andricus, and also noted several other previously published taxonomic changes involving Andricus species. Since then, Pujade-Villar et al. (2013b) described one species from the south-western USA, Pujade-Villar et al. (2017b) moved two species into the re-established Dros, and Zimmerman (2018) reestablished Trichoteras for a set of Andricus species galling Quercus section Protobalanus oaks. A new species of Andricus, A. notholithocarpi Melika, Nicholls & Stone, 2018, was described from California (Nicholls et al. 2018a), joining the species A. mendocinensis Weld, 1957 as the only Andricus species not galling a Quercus host, instead attacking the close relative Notholithocarpus (previously known as Lithocarpus densiflorus). Most recently Melika et al. (2021) moved one Andricus species into the new genus Disholandricus. Hence currently 91 Andricus species are known from America north of Mexico, associated with five different oak sections or genera of Fagaceae (Table 1).

Only two Andricus species, A. quercusfoliatus (Ashmead, 1881) and A. quercuslanigera (Ashmead, 1881), are known to associate with the oak section Virentes. Only one Andricus species, A. projectus Weld, 1952, is associated with Protobalanus oaks, while the species A. formosalis Weld, 1944, A. quercusformosus (Bassett, 1864) and A. longipennis (Ashmead, 1887) gall section Lobatae oaks.

Herein we describe 16 new species of Andricus of which five species are associated with Quercus section Lobatae, 10 species with section Quercus, and one species with section Virentes.