Echinothallis Skelley, Leschen & Liu 2021

Dacnini Character Variation and Tribal Placement of Echinothallis

Apart from the separate status of Languriidae sensu lato from the rest of Erotylidae (see Węgrzynowicz 2002, Le- schen 2003, and others), another family-group issue was reviewed by Boyle (1956: 77): “What to do with Dacne Latreille?” Long ago, Dacnini together with Tritomini (Böving & Craighead 1931), or Dacne alone (Edwards 1949) were once treated as Dacnidae. In this context, Boyle (1956) discussed the female terminalia of Dacne which have denticulate lamellae or comb rows on segment IX which is membranous (Figs. 12, 22). These were first described by Verhoeff (1895) and may be a unique feature in Coleoptera. They are found in other genera of dacnines and are used for boring holes into host fungi for egg deposition, as eloquently described in Boyle’s treatise. The distribution of the lamellae on segment IX is variable, and in Dacne there is always a dorsal and ventral pair, but a shorter lateral pair may be present and used to support the naming of subgenera. Lamellae are not, however, present in all dacnines and based on our available material, they are absent in Cardiodacne Philipp, Cnecosa Pascoe *, Combocerus Bedel, Cryptodacne Sharp *, Dacne (Afrodacne) Delkeskamp, Kuschelengis Skelley & Leschen *, Madadacne Philipp, Microsternus Lewis, and Neosternus Dhai & Zhao. Also, non-lamellate forms may instead have rows of asperities or straplike structures present on the membranes (see Skelley & Leschen 2007 figs. 32–33). Furthermore, the ovipositors may be modified from a normal form (Figs. 4, 37) by having hardened gonocoxites (Figs. 12, 22) that are chisel-like or stylate with reduced, laterally-placed, or absent gonostyli, occurring in non-lamellate (* above) and lamellate forms like Dacne (Dacne), Dacne (Xenodacne) Boyle, Microdacne n. gen., Masahiria Węgrzynowicz, Neothallis Fauvel and at least four species of Thallis Erichson which we have dissected, including the type species Thallis janthina Erichson (Lawrence 1988). This kind of variation in ovipositors may be linked to host fungal use and the hardness of their substrates like other erotylids (Węgrzynowicz 2002; Leschen 2003), but these characters will also be important in classification (e.g., Lawrence 1988). Furthermore, the variation in the distribution of glandular ducts (Drilling et al. 2013) among dacnines indicates a more complex pattern of relationships that may be tied directly with natural history.

Based on the inclusion of only three dacnine genera (Dacne, Combocerus, and Cryptodacne), Węgrzynowicz (2002: 470) characterized the Dacnini as beetles having a small body size, the last maxillary palpomere cylindrical, wing with cross-veins r 3 and r 4 close to, or touching one another, “the mesothoracic episternites meeting the mesepimera far anterad of the meso-metathoracical suture in the coxal cavity”, tarsomeres 1–4 cylindrical, and tarsomere IV either densely pubescent below or bearing two setae. The taxon sampling of Dacnini and included characters in Węgrzynowicz (2002) were not robust enough to draw any solid conclusions for the monophyly of all dacnines, but it is the first valuable attempt to define Erotylinae tribes based on morphology by coding of exemplar genera (Erotylinae were treated as tribes in Leschen 2003).

Returning to Echinothallis, this genus has some, but not all, defining characters of the dacnines. It also has a distinctly widened apical maxillary palpomere, unlike most members of the tribe. While some non-lamellate forms have a weakly dilated palpomere, the more securiform palpomere of Echinothallis is present in one form or another in all tribes. In the dacnines, dilated palpomeres are present in Cryptodacne and Cnecosa, the latter of which has ventrally recessed mouthparts that differ from Encaustini (Lawrence 1988). Echinothallis and Cryptodacne are also flightless and corresponds partly to the description of Sen Gupta’s (1970) Cryptodacnini, a synonym of Dacnini (Skelley & Leschen 2007; Bouchard et al. 2011). Cnecosa also has a securiform palpomere but it is fully winged (Skelley & Leschen 2007). Echinothallis also has a monocondylic meso-metaventral articulation coupled with a narrowed metaventral process, but not Cryptodacne, which has the typical dicondylic articulation and a widened metaventral process. Hoplepiscapha Lea has moderately widened metaventral process with either weakened dicondyly (Lawrence 1988) or a straight-line form. The meso-metaventral articulation varies in cucujoids (e.g., Leschen et al. 2005) and the dicondylic form is one synapomorphy for Erotylinae + Cryptophilinae, with some reversals (Leschen 2003). By including a large sampling of dacnine genera in a cladistic analysis and exploring the variation of female terminalia, traditional characters like the maxillary palpomere and meso-metaventral articulation, and novel characters like those identified on the metendosternite (Pecci-Maddalena et al. 2020), the monophyly of Dacnini can be better understood. For the time being, we tentatively retain various genera in the Dacnini and include Echinothallis.