Metallactus taeniatellus , Suffrian 1866
Creators: name: Sassi, Davide
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Chrysomelidae
Metallactus
Metallactus taeniatellus

description: Key to species of the Metallactus taeniatellus species group
In the following key some dorsal colour patterns are emphasized in the species identification process, but it should be borne in mind that the colouration is extremely variable within the species group, and intermediate specimens and outliers are rather common. For this reason, the shape of the aedeagal median lobe must always be studied for a reliable identification.
1. Pronotal yellow pattern includes a V-shaped or bilobed yellow spot close to the posterior margin just in front of the scutellum (Figs 4a, 7a, 9a, 10a), sometimes reduced to a narrow transverse marking (Fig. 8a)................................. 2
-. Pronotal yellow pattern lacking a V-shaped or bilobed yellow spot close to the posterior margin just in front of the scutellum. ................................................................................................... 6
2. Elytron yellow with two longitudinal black stripes transversally connected to each other once or twice at middle of elytron and just before the apical clivus (see also the “Remarks” in the description of M. superbiens for specimens coming from Rio Grande do Norte or the neighboring territories)................................................... M. uncinatus (Fig. 10)
-. Elytron mostly dark or yellow with a dark pattern but never arranged as above.................................... 3
3. Dorsal light pattern partly reddish (along elytral sides and, at times, pronotal sides) and partly yellow (pronotal midline, elytral apex, and sutural region). Elytral black pattern mostly consisting of a longitudinal stripe extended outward towards the lateral margin............................................................................. M. multicolor (Fig. 4)
-. Dorsal light pattern differently arranged................................................................... 4
4. Apex of median lobe of aedeagus with sides evenly rounded. Setose depressions weakly impressed, not delimited externally by a raised ridge, scarcely differentiated downward. Vasculum of spermatheca with a corkscrew-like appearance (Fig. 7g). Black colouration on elytra generally predominant............................................... M. superbiens (Fig. 7)
-. Apex of median lobe of aedeagus with more or less angulate sides (Figs 8c, 9c). Setose depressions more impressed, externally delimited by a raised, ear-shaped ridge, and giving rise downward to a deep pit devoid of setosity. Vasculum of spermatheca twisted at base but never corkscrew-like (Figs 8g, 9g). Black colouration on elytra generally less extensive, in form of longitudinal stripes or transverse band.......................................................................... 5
5. Ventral apical surface of aedeagal median lobe with wide, flat carina broadened apically to divide on each side, with a sharp ridge, each setose depression from the underlying pit (Fig. 9c), this pit rounded and deeper than the setose depression. In lateral view, shaft of median lobe with two evident bulges separated by a depression. Distal lobe of spermatheca rather long and slender. Black elytral pattern generally in form of a transverse band and never reaching elytral basal margin.. M. geiseri (Fig. 9)
-. Ventral apical surface of aedeagal median lobe with longitudinal ventral carina narrower (but larger in some specimens from Paraguay and Misiones, N. Argentina), separation between setose depression and underlying pit less evident (Fig. 8c), this pit shallower, more elliptical, and almost on the same plane as the setose depression. In lateral view, the outline of shaft less bulging (but, again, in Paraguayan specimens lateral profile might look rather like the one in M. geiseri). Distal lobe of spermatheca shorter. Black elytral pattern highly variable, often longitudinal and reaching elytral basal margin. Yellow spot close to posterior margin just in front of the scutellum generally reduced to a narrow transverse marking, more rarely V-shaped or bilobed..................................................................................... M. taeniatellus (Fig. 8)
6. Specimens smaller: male body length usually less than 3.5 mm; female body length less than 4.0 mm. Setose depression on ventral surface of aedeagal shaft shallowly impressed, separated by a flat, low carina.Aedeagus in lateral view slightly concave. Distal lobe of spermatheca rather long and slender, proximal lobe slightly swollen. Duct of spermatheca long, with loose turns close to vasculum. Dorsal colouration rather variable, but most common elytral black pattern in form of a transverse median band.............................................................................. M. latiusculus (Fig. 3)
-. Specimens larger: male body length usually more than 3.5 mm; female body length more than 4.5 mm. Setose depression on ventral surface of aedeagal shaft much deeper, separated by a robust, strongly raised longitudinal carina. Aedeagus in lateral view convex or almost straight. Proximal lobe of spermatheca not swollen or, if slightly swollen, distal lobe and duct short.. ................................................................................................... 7
7. Aedeagal apex lancet-shaped, moderately expanded, slightly larger than shaft. Aedeagus in lateral view almost straight with shallow depression toward base. Dorsal colouration of only available specimen extensively black with yellow markings along pronotal margins, middle of pronotal disc, humerus and elytral apex.............................. M. insitivus (Fig. 2)
-. Aedeagal apex truncate, with apical margin large and almost straight. Dorsal colouration variable...................... 8
8. Ventral aedeagal carina long and slender, with apex scarcely enlarged, delimited toward base by a deep notch (Fig. 1e). Distal lobe of vasculum short, proximal lobe slightly swollen. Duct of spermatheca short, rather rigid, with a few loose turns near vasculum. Dorsal colouration highly variable, but elytron most often mostly yellow with single rather short and straight longitudinal black stripe. Female pronotum often yellow with squared black marking on disc................ M. cultus (Fig. 1)
-. Ventral aedeagal carina shorter, with a button-like apex, delimited toward base by a rounded bulge (Figs 5e, 6e). Proximal lobe of vasculum not swollen................................................................................ 9
9. Aedeagal median lobe with apex roughly square, with sides straight, more raised, and not perceptibly notched in lateral view (Fig. 5e). Distal lobe of vasculum short. Duct of spermatheca short, usually with several closer turns near vasculum......................................................................................... M. planipennis (Fig. 5)
-. Aedeagal median lobe with apex roughly subpentagonal, with sides angulate, less raised and perceptibly notched in lateral view (Fig. 6e). Distal lobe of vasculum long. Duct of spermatheca short, with few loose turns near vasculum.................................................................................................... M. quadrinus (Fig. 6)
description: Published as part of Sassi, Davide, 2022, Revision of the Metallactus taeniatellus species group (Coleoptera: Chrysomelidae: Cryptocephalinae), pp. 251-282 in Zootaxa 5125 (3) on pages 254-255, DOI: 10.11646/zootaxa.5125.3.1, http://zenodo.org/record/6443765