Rhizophagus diaboli, Dodelin, 2021

Barnouin, Thomas, Vincent, Alexis & Soldati, Fabien, 2025, Rhizophagus atticus Tozer, 1968 in France: synonymy with R. diaboli Dodelin, 2021, distribution and ecology (Coleoptera: Monotomidae), Zootaxa 5691 (2), pp. 329-340 : 333

Rhizophagus diaboli compared with R. depressus

Dodelin (2021) described several characters that distinguish R. diaboli from R. depressus , which have been tested by studying the material examined.

We confirm that the shape of the antennal club is a valid character to distinguish both species. In R. diaboli , the antennal club is sub-truncate, with the 11 th antennomere embedded in the 10 th ( Fig. 12 ), whereas the club of R. depressus is ovoid, with the 11 th antennomere clearly protruding from the 10 th ( Fig. 13 ). However, this characteristic may sometimes prove ambiguous due to a slight variability in the conformation of the 11 th antennomere in R. diaboli . In addition, the angle of observation can also influence the perception of this morphological character.

Moreover, we can verify that the characters based on the male genitalia distinguish the two species. Firstly, the median lobe of R. diaboli seen in profile is short and regularly curved up to the apex ( Fig. 18 ), whereas that of R. depressus is clearly longer, curved over the basal third of its length and then sub-rectilinear up to the apex ( Fig. 19 ). This character separates the two species. The arrangement of the setae on the median lobe is also a diagnostic feature. However, while the presence of a small tuft of long setae in the apical third of the ventral face of the median lobe is confirmed in R. depressus ( Fig. 19 ), the representation and description of the arrangement of these setae in R. diaboli is imprecise.Admittedly, only small setae are found on the apical margin of the genitalia, but these setae form a crown along the entire margin and not just on the ventral area ( Fig. 18 ). Finally, the sclerites of the endophallus, visible on the dorsal surface of the median lobe, differ in configuration between the two species. The medial sclerite of R. diaboli is broad and rectilinear while it is fine and strongly arcuate in R. depressus . Moreover, the branches of the anterior sclerite are straight while they are strongly sinuate in R. depressus . Although the representations of these internal parts are somewhat approximate, the configurations we observed are quite different and consistent with the proposed photos ( Figs. 15, 16 ).

According to Dodelin (2021), the cuticle on the dorsal surface of R. diaboli is smooth and shiny, the microreticulation visible only at very high magnification (x70), whereas it is strongly micro-reticulated in R. depressus , giving it a dull appearance. The microreticulation of the pronotom and elytra is highlighted by the author as one of the main characters distinguishing the two species. However, the study of abundant material from France leads to the invalidation of this character. Indeed, while a fine but clear microreticulation is always present on the pronotum in R. depressus ( Fig. 10 ), the punctation of the pronotum is highly variable in R. diaboli , ranging from a smooth, shiny pronotum with imperceptible microreticulation ( Fig. 8 ) to a dull pronotum with very strong microreticulation ( Fig. 9 ). Moreover, the dull form is more common and more widespread than the shiny form. Both forms can cohabit at the same site. In this case, one of them dominates, with a ratio of more than 10 to 1.

According to our studied material, there is indeed a subtle difference in the shape of the pronotum between both species. However, the differences described by Dodelin (2021) are exaggerated and, above all, imprecise, as the author does not consider the sexual dimorphism of this character in most of species within the genus ( Peacock 1977). The pronotum of the male of R. diaboli is barely longer than wide, with straight, subparallel to divergent margins, narrowing slightly at the apex ( Fig. 8 ), whereas that of the female is as long as wide, with straight subparallel margins narrowing progressively from the anterior fourth ( Fig. 9 ). In R. depressus , the pronotum of the male is as long as wide, with straight, subparallel or barely divergent margins, narrowing progressively over the anterior third, whereas that of the female, with straight, subparallel margins, narrows abruptly in the anterior quarter ( Fig. 10 ).

Although the use of certain characters has been invalidated (punctation of the pronotum) or clarified (shape of the pronotum and arrangement of the setae on the median lobe of the male genitalia), the diagnosis presented leaves no doubt as to the existence in France of a third species in the subgenus Eurhizophagus , closely related to R. grandis and R. depressus , corresponding approximately to the description of R. diaboli . It may be added that there is an overlap in size between both species, R. diaboli being generally smaller (2.5–3.6 mm; median=2.9 mm) and more compact than R. depressus (2.9–4.2 mm; median=3.3 mm).

Figures

FIGURES 5–13. Figures 5–6. Habitus—5. R. atticus from France, ♀, 3.0 mm. 6. R. depressus from France, ♀, 3.6 mm. Figures 7–10. Pronotum—7. R. atticus, holotype ♂. 8. R. atticus, shiny form, from France, ♂. 9. R. atticus, microreticulate form, from France, ♀. 10. R. depressus, from France, ♀. Figures 11–13. Antennal club—11. R. atticus, holotype ♂. 12. R. atticus, from France. 13. R. depressus, from France. (Photos: Alexis Vincent).

FIGURES 14–19. Figures 14–16. Median lobe of aedeagus with internal sclerites (dorsal view)—14. R. atticus, holotype ♂. 15. R. atticus, from France. 16. R. depressus, from France. (Photos:Alexis Vincent). Figures 17–19. Median lobe of aedeagus (lateral view)—17. R. atticus, holotype ♂. 18. R. atticus, from France. 19. R. depressus, from France. (Photos: Alexis Vincent).