Geochus

Leschen, Richard A. B., Davis, Steven, Brown, Samuel D. J., Brav-Cubitt, Talia & Buckley, Thomas R., 2022, The Enigmatic Dead-Leaf Miner Geochus Broun (Coleoptera: Curculionidae): Phylogenetic Placement, a New Species, and Lectotype Designations, The Coleopterists Bulletin 76 (1), pp. 1-35 : 5-8

CLASSIFICATION OF GEOCHUS

The unstable classification of Geochus , mainly by Thomas Broun, exemplifies the difficulties in- volved in the higher classification of the Curculionidae . The general lack of synapomorphies for many, if not most, weevil tribes and subfamilies creates problems when attempting to place anomalous taxa such as Geochus . Here, we review the various hypotheses for the placement of Geochus and, based on molecular data, we argue that it is a member of the Viticiini. Future molecular study of Cyclominae and Phrynixini within the context of a broader study of the CEGH clade would help to strengthen this hypothesis.

Diabathrariini. Geochus was placed here by Broun (1880), Klima (1935), and Kuschel (1990). The current conception of the tribe is presently lim- ited to three African genera, Aphanonyx Marshall , Onychogymnus Quedenfeldt , and Diabathrarius Schoenherr (Caldara et al. 2014: 607) , although historically some Australian genera have been sug- gested to be in the group ( Klima 1935; Oberprieler 2010). Like Geochus , these Diabathrariini have lost tarsomere 5. However, unlike Geochus , they are not present in leaf litter and have a dense vestiture of broad, fluted scales, a deep prosternal depression into which the rostrum can be concealed, and strong unci on the tibia. No representatives of the Diabathrariini have yet been included in any published phylogenetic analyses. However, their current classification in the Curculioninae (Caldara et al. 2014: 607) conflicts with the results of our phylogeny that places Geochus outside the CCCMS. Although our molecular data are insufficient to reject the hypothesis of Geochus being related to Diabathrarius , we consider a relationship between the genera unlikely based on the different biology, vestiture and tibial armature. However, further research will be required to critically examine the relationship of Geochus with respect to the Diabathrariini.

Cylindrorhinidae/Brachyderidae/Otiorhynchidae. Geochus was placed in these family-group taxa by Broun (1880, 1881, 1886, 1893a, b). These taxa are currently tribes within the Entiminae ; however, Broun’s composition of these groups differed substantially from modern conceptions. Most of the taxa that Broun placed in these groups (e.g., Cylindrorhinidae [ Inophloeus Pascoe ]; Brachyderidae [ Nicaeana Pascoe ]; Otiorhynchidae [ Brachyolus White ]) are now considered to be Entiminae : Tropiphorini (Alonso-Zarazaga and Lyal 1999; Leschen et al. 2003). However, Broun also included some non-entimine weevil genera: e.g., Paedaretus Pascoe (in Cylindrorhinidae; now Molytinae incertae sedis), Lyperobius Pascoe (in Cylindrorhinidae; now Molytinae : Hylobiini ), Aglycyderes Sharp (= Aralius Kuschel ) (in Brachyderidae; now Belidae : Oxycoryninae), and Rhadinosomus Schoenherr (in Brachyderidae; now Cyclominae : Aterpini). In common with Geochus , all these genera share a relatively short rostrum. However, Geochus cannot be retained in the Entiminae because of the absence of mandibular cusps (present in most entimine weevil groups; Marvaldi et al. 2014) and long larval antennae. In our phylogeny, Geochus did not form a clade with the sampled entimine genera ( Chalepistes Brown , Irenimus Pascoe , Epitimetes Pascoe , and Catoptes Schoenherr ). We reject this hypothesis.

Hylobiidae (sec Broun). Geochus was placed in this nominal family-group taxon by Broun (1914a); however, Broun’s conception of the taxon differed substantially from Hylobiina ( Molytini ) as presently classified ( Lyal 2014), and none of the taxa he included in this group ( Eiratus Pascoe , Exeiratus Broun , and Dryopais Broun [now in Steriphus Erichson ]) are presently considered to belong to the Molytini . Eiratus differs from Geochus by having a long, subparallel rostrum, with oblique scrobes; the funicle inserted sub-apically into the scape; tarsomeres 1 and 2 being much thinner than tarsomere 3 and nearly nude underneath; and tibiae possessing premucrones and large unci that arise from the dorsal margin. Geochus has a short rostrum which wid- ens apicad and deep, nearly vertical scrobes; the funicle is inserted apically into the scape; tarsomeres 1 and 2 are about as broad as tarsomere 3 and are densely clothed with setae ventrally; and the tibiae have a mucrone that arises submedially and lack premucrones. Eiratus and Exeiratus were both included in our phylogeny but were not closely related to Geochus . Nor were they particularly closely related to each other, with Eiratus being resolved as sister to Catolethrobius Voss and Allaorus Broun , and Exeiratus being resolved as sister to Phronira . These genera were in separate clades, which were part of an unresolved trichotomy with Cossoninae + Rhamphini . We reject this hypothesis.

Cryptorhynchini . Geochus was placed here by Lea (1927). He did not elaborate on his rationale, although we surmise that phenetic similarities between Geochus and the many small leaf-litter inhabiting cryptorhynchine weevils with which Lea was familiar (e.g., Hoplodecilaus Lea , Gymnoporopterus Lea , and species of Decilaus Pascoe ) are likely to have influ- enced this decision. Cryptorhynchini have a deep prosternal channel with a mesoventral receptacle into which the rostrum rests when in thanatosis (Riedel et al. 2016). Geochus lacks this mesoventral receptacle, at most possessing a slight depression that may be margined laterally and posteriorly. Geochus was not grouped with the cryptorhynchine weevil taxa includ- ed in our phylogeny ( Adstantes Lyal , Zeacalles Broun , Scelodolichus Broun , Synacalles Lyal ). For these rea- sons, we reject this hypothesis.

Cryptoplini (= Haplonychinae). Geochus was placed here by Broun (1914b, 1921, 1923), Marshall (1946), and Zimmerman (1994). This tribe currently includes five genera: Cryptoplus Erichson , Haplonyx Schoenherr , Menechirus Hartmann , Sigastus Pascoe , Zeopus Pascoe , and Kuschelorhynchus Jennings and Oberprieler. The group notably shows a graded reduction in the development of their tarsal claws, with species of Sigastus having two tarsal claws, most Haplonyx having a single claw, and most species of Cryptoplus and Zeopus having no tarsal claw what- soever (Jennings and Oberprieler 2018). However, these latter genera retain tarsomere 5, albeit heavily reduced. This reduction of the tarsal claws and ap- parent loss of tarsomere 5 were presumably key mo- tivations for linking Geochus with the Cryptoplini . However, this has not been explicitly stated by most of the authors who have made such an action. The members of Cryptoplini share a long rostrum; flattened tibiae, frequently armed with a tooth on the ventral margin; a premucro and an uncus on the pro- tibial apex; a spermathecal gland with a sclerotized base; and a penis with a tectal plate fused to the base of the pedon (Jennings and Oberprieler 2018). In contrast, Geochus has a short rostrum; cylindrical tibiae that are never armed along the ventral margin and have a submedial mucrone at the apex; an unsclerotized base of the spermathecal gland; and a penis that lacks a tectal plate. Although no representatives of Cryptoplini were present in our data set, specimens of Cryptoplus and Haplonyx were weakly placed in a clade with Orthorhinus ( Molytinae ) and strongly resolved within the CCCMS clade in other published phylogenies (Gunter et al. 2016).We reject this hypothesis.

Rhamphini . Geochus was placed here by May (1993) and Kuschel in Leschen et al. (2003), as a result of the discovery that the larvae of Geochus are leaf-miners. Rhamphini is best known from the Northern Hemisphere, although members of the tribe are present in Australia and the South Pacific (Kojima and Morimoto 1996). Members of Rhamphini also typically have enlarged metafemora for jumping, slender tarsomeres 1 and 2, and long, ventrally directed rostra with the antennae inserted medially or basally with vague scrobes. These differ from the simple femora, broad tarsomeres and short rostrum with deep scrobes possessed by Geochus . May (1993) mentioned that the leaf-mining larvae of Rhamphini ( Curculioninae ; Rhamphus and Rhynchaenus ) resemble Geochus , but differ from Geochus by having a more falcate mandible and a broader and possibly more setose labrum. Other larval features shared by these taxa, such as the flattened form with lateral extensions, reduced cephalic chaetotaxy, and the endocarina extended posteriorly, may represent convergent morphologies from their similar biology. The Rhamphini were resolved as monophyletic by Gunter et al. (2016), while our phylogeny did not resolve the relationships between the included Rhamphini ( Orchestes Illiger , Isochnus Thompson , and Rhamphus ), Exomesites , and Afrogeochus . However, our molecular data do not place Geochus in this clade, and we reject the hypothesis of Geochus being in the Rhamphini .

Phrynixini. Geochus was placed here by Pullen et al. (2014), Lyal (2014), and Legalov (2020). Legalov (2020) established a subtribe, Geochina Legalov, within the Phrynixini to accommodate Geochus , Afrogeochus , and a genus he later described from the Philippines as Orientogeochus Legalov ( Legalov 2021) . Phrynixini is a group of apterous species Kuschel (1964, 1972) named for taxa occurring in Australia, Chile, New Zealand, and New Caledonia. The members of the tribe share many adult characters with Geochus , including the metanepisternal suture (if present), which lacks sclerolepidia. The prosternal groove is absent in Phrynixini ( Kuschel 1964, 1972), and in Geochus there is an impression, but not a well-formed groove as is found in many molytine weevils. These tho- racic features are valuable in higher-level placement but are often lost in flightless forms that have reduced or completely absent hind wings ( Fig. 9F ), as is the case for Geochus and all Phrynixini ( Kuschel 1964, 1972). The rostrum retains several important features, including the pharyngeal plate (Davis 2017). The pharyngeal plate in Geochus shows similarity to those found in Phrynixini and some Entiminae (Davis 2014, 2017), albeit slightly reduced in form, in the weak, anteriorly converging posterior arms of the plate, the complete sclerotiza- tion of the plate (absence of any holes), and poste- rior-projecting lateral margins of the plate ( Figs. 10E , 11E–F ). However, Geochus differs from phrynixines by its leaf-mining larva and, in the adult, a reduced tegmen which forms a complete membranous ring, lacking the parameres in some species, and a sternite IX (spiculum gastrale) which lacks posterior arms. Furthermore, the ovipositor is entirely membranous in Geochus and present in Phrynixini but is lost in some Cyclominae ( Oberprieler 2014) and a very few Entiminae ( Marvaldi et al. 2014) . Our molecular data do not support a placement with the phrynixine genera included, and we reject this hypothesis.

Afrogeochus . The similarities of Afrogeochus to Geochus are superficial. Our molecular data support its placement in Cossoninae , supported by the 5-5-5 tarsal formula and tarsomere 4 inserted into a broad- ly bilobed tarsomere 3, which is also present in the similar Philippine genus Orientogeochus ( Legalov 2021) . Furthermore, both genera differ from Geochus by having the funicle inserted subapically into the scape and tarsomeres 1 and 2 being signifi- cantly narrower than tarsomere 3.

Placement of Geochus in Viticiini. Based on phylogenetic analysis of the molecular data collect- ed during this research, we conclude that Geochus is closely related to Viticis within the larger PHCE grade. Our results unequivocally exclude placement of Geochus within the Curculioninae or Molytinae and concur with Lyal (2014) and Pullen et al. (2014) that the genus is located somewhere among the CEGH clade. In addition to Viticis , the Viticiini Morimoto, 1983 include the genera Austrocis Zimmerman and Oberprieler , Peliocis Lea , Aviticis Kojima and Morimoto , Samoacis Zimmerman , Eupholocis Lea , Platynotocis Lea , and Tivicis Morimoto. Like Geochus , many of the genera currently included in the tribe have been variously placed in the Entiminae ( Ottistirini ) (Zimmerman 1939), Diabathrariini (Zimmerman 1936), Cyclominae (Alonso-Zarazaga and Lyal 1999) , and Curculioninae (Alonso-Zarazaga et al. 2017; Caldara et al. 2014). All species for which the biology is known are leaf-miners, mainly of Elaeocarpaceae or Moraceae ( Kojima 2006; Maunsell et al. 2017; Oberprieler 2010; Pullen et al. 2014). Morphological features that unite Geochus with Viticis and Samoacis include funicles which are apically inserted into the scape (possibly subapically in Tivicis ); a short, oblique comb on the anterior face of the tibiae; broad tarsomeres 1 and 2; and ovipositors with gonocoxites strongly reduced, largely membranous, and which lack styli.

The reduction or lack of tarsomere 5 (onychium; see Caldara et al. 2014), with or without claws, is a feature of this group. Although no viticiine weevil larvae have been described in detail, the “long antenna” that the larva of Austrocis bicaudatus Zimmerman and Oberprieler is reported to possess ( Oberprieler 2010) may be a synapomorphy shared with the long antenna found in Geochus larvae ( May 1993). Our placement of Viticis among the broader CEGH group is consistent with previous phylogenetic results (Gunter et al. 2016) and contradicts the placement of the tribe in Curculioninae (e.g., Caldara et al. 2014). The Viticiini are themselves divided into two groups according to Caldara et al. (2014), one corresponding to the original definition of the tribe ( Morimoto 1983) having the funicle with six antennomeres, separated procoxae, and dentate femora; the other having the funicle with seven antennomeres, contiguous procoxae, and unarmed femora. Geochus has characters of both groups, having seven-segmented funicles and unarmed femora, but separated procoxae. Geochus is quite unusual in form from other Viticiini, for example, with respect to the equal widths of the tarsomeres. Unlike Geochus , both Viticis and Samoacis have tarsomeres 1 and 2 becoming progressively narrower than tarsomere 3, whereas tarsomere 1 is about as wide as tarsomeres 2 and 3. Otherwise, all Viticiini have tightly articulated tarsomeres, with tarsomeres 2 and 3 equal or subequal in size.

We believe that Orientogeochus does not belong among Viticiini: the long, subcylindrical form of the scape in Orientogeochus differs from the short, clavate, and slightly curved shape of the scape in Viticiini. The pedicel of Viticiini is relatively large and globular. The scape is inserted laterally into the middle of the rostrum in Viticiinae , with a definite ventrally directed scrobe, unlike the sub-apically inserted scape with a foveiform scrobe present in Orientogeochus . The tarsi of Orientogeochus show a much greater ratio in the width of tarsomeres 3 and 2 than can be seen in the other Viticiini. Other features of the Orientogeochus description which are inconsistent with other Viticiini are the length of the rostrum, the structure of the ventral teeth on the femora (a single large and medially sited tooth in Orientogeochus ; two small basally sited teeth in Viticis but absent in many other Viticiini, including Geochus ), and the structure of the abdomen (Viticiini have abdominal ventrites 1 and 2 subequal in length and being somewhat convex, but longer than the metaventrite, and each one being longer than ventrites 3–5 combined). The placement of Orientogeochus needs further study.

Concerning the validity of Geochina as a subtribe within Viticiini, a more detailed morphological study of the tribe is required, in addition to more comprehensive genetic sampling.

Figures

Fig. 9. Geochus kuscheli, new species, male (A–C) and female (D–E) terminalia, confocal microscope images. A) Aedeagus, dorsal view, B) Aedeagus, lateral view, C) Sternites VIII (with spiculum gastrale) and IX (arrow), D) Sternite VIII and spermatheca, E) Enlargement of spermatheca in D.

Fig. 10. Geochus kuscheli, new species, confocal microscope images. Mouthparts: A) Labium, ventral view, B) Maxilla, ventral view, C) Left mandible, dorsal view, D) Right mandible, dorsal view. E) Dorsal view of the apicoventral portion of rostrum showing pharyngeal plate (arrow), F) Lateral view of meso- and metathorax showing reduced hind wing.

Fig. 11. Geochus inaequalis, confocal microscope images. Mouthparts: A) Labium, ventral view, B) Maxilla, ventral view, C) Left mandible, dorsal view, D) Right mandible, dorsal view. E) Ventral portion of rostrum apex with mouthparts (mandibles removed), showing pharyngeal plate (arrow), F) Pharyngeal plate showing the location of the anterior and posterior arms, and the fully sclerotized base of the plate (arrow).