Synobius Sharp, 1899

Halstead, David G. H., 2020, New and little known Coleoptera (Silvanidae: Silvaninae) from Central and South America, Insecta Mundi 2020 (842), pp. 1-37 : 2-3

Synobius Sharp

Synobius Sharp 1899: 558 .

Discussion. Synobius Sharp is a little-known genus containing two described species, Synobius lobicollis Sharp, 1899 , described from Panama, and Synobius lobatus ( Grouvelle, 1896) , from Brazil. Grouvelle originally described his species in Nausibius and, although differing from this genus in general facies, it does seem to be more closely related to it than any other in the family. Grouvelle (1913) transferred his species to Synobius remarking that an examination of the figures of S. lobicollis and S. lobatus showed these species were very closely related. Indeed, one of the labels that he attached to his holotype following the establishment of the new genus by Sharp, suggests he thought that they might be conspecific.

Sharp, when describing the genus, remarked that it was apparently allied to Nausibius , Cathartus Reiche and Hapalips Reitter (the last of these is now placed in the Erotylidae ). He stated that ‘… the greatest peculiarity of the genus is the peculiar, glabrous, rigid antennae.’ and drew attention to the fact that the structure of the sterna is that normal in the ‘Silvanides’. In his accompanying species description, Sharp anticipated a myrmecophilous or termitophilous habit for this insect. The habitat data on the majority of specimens examined (see descriptions below) tends to confirm an inquiline relationship as they were found in nests of bees of the genus Trigona Jurine (Apidae) .

Diagnosis. This genus ( Fig. 1–17 , 123 ), as represented by the two known species, may be distinguished from Nausibius by its antennae, which have a very small, narrow terminal segment; the pronotum, which is without lateral teeth, has a strong indentation before the anterior angles that form rounded and in front slightly declivous lobes; and the elytra, which lack obvious striae (an unusual condition in Nausibius although it does occur). The tarsi in Synobius are simple ( Fig. 2 ) and there are no antennal grooves on the head. Obvious secondary sexual characters have not been found although with larger individuals, more transverse pronota may be indicative of females, as is often the case in Nausibius and some other silvanine genera.

Apart from the types in the MNHN ( S. lobatu s) and NHML ( S. lobicollis ) the species are known to the author only from a small number of specimens from Nevermann’s collection made in the 1930s and now mainly in the USNM, but also NHML and MIZP (just S. lobicollis in these last two depositories). Nevermann believed that his material represented two new species and labelled the specimens as such but did not publish descriptions. Comparison of Nevermann’s specimens with S. lobatus and S. lobicollis has shown that they represent these two extremely similar and very obviously closely related taxa, which are maintained here as distinct species and redescribed.

Figures

Figures 1–6. Synobius lobatus (Grouvelle), male. 1) Habitus. 2) Metatarsus. 3) Antenna, enlarged (1–3 holotype). 4–6) Genitalia. 4–5) Parameres and median lobes to show variation. 4) Narrower median lobe, specimen from Brazil, Est. Paraná, Rio Negro. 5) Broader median lobe, holotype specimen from Brazil, Rio Grande do Sol. 6) Paramere, enlarged apical region. Scale lines for Figure 1 = 2.0 mm, for Figures 4 and 5 = 0.2 mm.

Figures 7–10. Synobius spp. pronota. 7–8) S. lobatus (Grouvelle). 7) Male, 8) Female. 9–10) S. lobicollis Sharp, both male. Scale line = 2.0 mm.

Figures 11–17. Synobius lobicollis Sharp, male. 11) Habitus. 12) Head, anterior lateral region showing antennal base and eye. 13) Antenna, enlarged. 14–17) Genitalia and associated sternites. 14) Genitalia, without internal sac. 15) Paramere, enlargement of apical half. 16) Internal sac, apical third. 17) Sternites 8 and 9. Scale lines for Figure 11 = 2.0 mm, for Figures 14 and 16–17 = 0.5 mm.

Figures 123–124. Color habitus photographs.123) Synobius lobatus (Grouvelle). 124) Pensus hirtus, new species.