Rhadalus LeConte, 1852

Gimmel, Matthew L. & Mayor, Adriean J., 2022, Synonymic and Nomenclatural Notes in the Mauroniscidae and Rhadalidae (Coleoptera: Cleroidea), The Coleopterists Bulletin 76 (3), pp. 419-422 : 420-421

Rhadalus LeConte, 1852

The genus Rhadalus was originally described for a single North American species, Rhadalus testaceus LeConte, 1852 , based on a single male specimen from near the Colorado River in California (photographs at MCZbase 2022). Only one North American species has since been added to the genus, Rhadalus lecontei Casey, 1895 , based on a single female specimen from Benson, Cochise Co., Arizona. Additional species from south of the United States were added to the genus upon the synonymy of Cymbolus Gorham, 1886 with Rhadalus by Peacock (1987: 144).

According to Casey’s (1895: 605) key, the characters to separate R. lecontei from R. testaceus are: eyes small, separated on frons by nearly 3× own width (vs. separated by less than 2× own width in R. testaceus ), and by having a pronotum nearly as wide as the elytra (vs. “very much narrower than the elytra” in R. testaceus ). However, based on our examination of a wide range of specimens, both characters are apparently sexually dimorphic, with the males having much larger eyes than females and females having a wider pronotum than males. Casey (1895) believed LeConte’s type of R. testaceus to be a female based on abdominal ventrite 5 being “evenly and broadly rounded behind”, similar to that of the R. lecontei type. However, ventrite 5 is broadly, very shallowly arcuate in the type of R. testaceus , consistent with our observations of male specimens, which range from shallowly arcuate to truncate. In females, ventrite 5 is broadly but more strongly arcuate than that of males. The antennae are also sexually dimorphic, being distinctly longer in males.

After examination of the original descriptions in light of newly collected material, we propose the following subjective synonymy:

Rhadalus testaceus LeConte 1852: 212 .

Rhadalus lecontei Casey 1895: 606 . New junior synonym.

As a consequence of the above synonymy, only a single species of Rhadalus , R. testaceus , is recognized to occur north of Mexico. We have examined specimens from California and Arizona; additional specimens have been reported from Nevada and New Mexico on BugGuide (www.bugguide.net).

There are six additional species of Rhadalus recorded from Mexico south to Paraguay. However, one species not mentioned in the review by Peacock (1987), Rhadalus asiaticus ( Pic, 1951) , but currently assigned to that genus based on the aforementioned synonymy of Cymbolus with Rhadalus , was described from “Tuhang”, a previously unknown locality in Asia ( Mayor 2007). In this context, Muséum national d’Histoire naturelle, Paris (MNHN) hosts the holotypes of two relevant species briefly described by Maurice Pic (1951): Microcymbolus modestus Pic, 1951 and Cymbolus asiaticus Pic, 1951 . These were examined in detail by the late Karel Majer, but the results of his observations have remained unpublished until now. Our colleague Robert Constantin (in litt.) kindly provid- ed following details on these specimens.

Type Specimens. Microcymbolus modestus , one female, labeled as follows, deposited in MNHN: holotype female [mounted on card], “ SAIGON /1.I.[19]51/ J. Barbier [white printed and handwritten label]//5532 [white handwritten label]// TYPE [red printed label]// Microcymbolus n.g. modestus n.sp. //Dasytide [white handwritten label]// voisin/ Cymbolus [white handwritten label]//genre douteux/ à voir d’autres/désiré [dubious genus/see others/specimen wanted] [white handwritten label]// plus petit/ponctuation plus forte/plus dense au thorax [white handwritten label]//Procerallus haplocnemiformis (voir v. diversepunctatus Pic ) [white handwritten label]// Holo- /typus [red printed label]// Microcymbolus Pic /syn. to Malthacodes ,/ modestus (Pic) , ♀ / K. Majer det. 1989/ Holotypus [white handwritten and printed label]” .

Cymbolus asiaticus , one female, labeled as follows, deposited in MNHN: holotype female [mounted on card, antennomeres 3–11 of right antenna missing], “ PAHANG F. M. S. [Federal Malay States]/ Gunong Tahan Padrang [possibly Gunung Tahan , 4°37′E, 102°12′E]/ Sebrang 4900 ft / Dec 19th 1923 / H.M. Pendlebury [white printed and handwritten label]//? Cymbolus /asiaticus/n. sp. [white handwritten label]// TYPE [red printed label]// Holo- /typus [red printed label]// Cymbolus asiaticus Pic /syn. n. to ♀ / Malthacodes modestus / K. Majer det. 1989/ Holotypus [white hand written and printed label]” .

These two females appear morphologically identical and the synonymy proposed by K. Majer is accepted as such. The subjective synonymy is indicated below:

Microcymbolus modestus Pic 1951: 13 .

Cymbolus asiaticus Pic 1951: 13 . New junior synonym.

Rhadalus asiaticus : Mayor 2007: 415. Distribution: Malaysia (Pahang), Vietnam.

Majer’s determination labels (see above) suggest not only that C. asiaticus is a junior synonym of M. modestus , but that M. modestus should be transferred to the genus Malthacodes Waterhouse, 1876 (type species: Malthacodes pictus Waterhouse, 1876 ). This would mean treating Microcymbolus Pic, 1951 as a junior synonym of Malthacodes , something we are reluctant to do until we have the opportunity to carefully examine all relevant types and type species.

As a consequence of the above synonymy, Rhadalus is recognized as an exclusively New World genus.