Caenotus

Metz, Mark A., 2003, Description of a new species of Caenotus Cole (Diptera: Scenopinidae) from Baja California Sur, Mexico, with a review of the genus, Zootaxa 223, pp. 1-11 : 2-3

Taxonomy of Caenotus

Cole (1923) first described the genus in the family Therevidae based on two new species, C. inornatus Cole and C. minutus Cole , noting, “The genus is not closely related to any other described from North America.” Melander (1928) transferred the genus to the family Bombyliidae in the subfamily Heterotropinae and later ( Melander 1950) described two new species, C. canus Melander and C. hospes Melander. A fifth species, C. thompsonii Evenhuis , was described ( Evenhuis 1977), then Caenotus was placed in Proratinae ( Evenhuis 1991), a bombyliid subfamily described for the genus Prorates Melander ( Theodor 1983) . Yeates (1992) addressed the familial placement of the proratine genera with morphological cladistic analysis and removed the subfamily from Bombyliidae , placing these genera (sans Apystomyia Melander ) in Scenopinidae and described a new scenopinid subfamily, Caenotinae, for the genus Caenotus .

Nagatomi et al. (1994) treated the genus extensively as a member of the Proratinae. They described a new genus, Aceaenotus Nagatomi & Yanagida, for C. canus and described a new species, C. mexicanus Nagatomi & Yanagida , collected from San Luis Potosi, Mexico. They examined all the described species, except C. thompsonii , and had only male specimens of C. minutus and only female specimens of C. inornatus available.

Yeates (1992) demonstrated two non­homoplasious synapomorphies for the genus as a result of his phylogenetic analysis, which included the two species C. inornatus (the type species) and C. hospes . Both species possessed a membranous connection between the prosternum and the propleuron (Character 6. Prosternum separate from the propleuron) and a pair of anteriorly projecting, dorsal structures originating from the dorsum of the phallus (Character 25. Male genitalia with a long, narrow apodeme [phallus sheath apodeme] extending anteriorly and parallel to the ejaculatory apodeme and gonocoxal apodemes). The presence of wing vein M 3 in C. inornatus was considered a plesiomorphic retention (present in the outgroup taxa) thus making the loss of vein M3 a homoplasious forward change in C. hospes and in the rest of Scenopinidae ( Yeates 1992, Fig. 65).

Nagatomi et al. (1994) listed putative synapomorphies for their hypothesis of the genus without support from a tree hypothesis based on a data matrix. These included: antennal segment 1 longer than segment 2, mesonotum and scutellum without bristles, vein R5 ending below wing apex, female abdomen longer and roughly 3 times as long as mesonotum + scutellum, and basiphallus with a pair of anterolateral dorsal processes. They did not include the species C. thompsonii in their treatment of the genus. The argumentation for the removal of the species C. canus is indirect, but several morphological similarities to the species in Proratinae sensu stricto suggest this hypothesis will withstand cladistic scrutiny.

The new species described herein possesses the synapomorphies supported by Yeates’ (1992) analysis. The anteriorly projecting structures of the aedeagus apparently originate from the phallus itself, rather than the parameral sheath, suggesting that these structures might be homologous with lateral ejaculatory sclerites. Dissections of preserved adult males would provide definitive support as these structures provide the origin of muscle M32 ( Ovtshinnikova & Yeates 1998). The new species also possesses the characteristics listed by Nagatomi et al. (1994), but I do not consider these diagnostic or synapomorphic for the genus.