Bruchus gibbithorax Schaeffer, 1904:230

Romero, Jesus & Johnson, Clarence Dan, 2003, Revision of the Genus NELTUMIUS Bridwell (Coleoptera: Bruchidae), The Coleopterists Bulletin 57 (2), pp. 219-236 : 225-228

Bruchus gibbithorax Schaeffer, 1904:230 (Pinal Mountains, Arizona); Fall 1910:162;

Pic, 1913:27. Mylabris gibbithorax: Leng 1920:305 . Neltumius gibbithorax: Johnson 1968:1270 ; Bottimer 1968:1025; Center and Johnson

1976:196; Kingsolver et al. 1977:115; Johnson 1978:438, 1980:28; Ward et al.

1977:6; Johnson and Kingsolver 1981:416; Johnson 1983 a:28; Johnson

1983 b:35; Johnson 1983 c:32; Udayagiri and Wadhi 1989:95. N. gibbothorax (sic): Bradley 1947:36; Kingsolver 1964:105. N. gibbothorae (sic): Blackwelder and Blackwelder 1948:45.

Description. Male. Integument Color. Head, thorax, abdomen, and tarsi black; femora and tibiae brown; antenna dark brown.

Vestiture. Frons densely clothed with gray and pale yellow hairs; antenna black with gray pubescence; disk densely covered with pale yellow and gray hairs; antescutellar area lighter gray; scutellum covered with white pubescence; elytra clothed with brown, pale yellow, and gray hairs in distinctive pattern ( Fig. 7 ); sides and venter with intermixed gray and pale yellow hairs, short tuft of gray hairs in middle of first abdominal sternum; legs evenly clothed with gray hairs; pygidium uniformly clothed with gray and pale yellow intermixed hairs, sometimes with indistinct darker spot in middle.

Head. Antenna with first four segments and the last filiform, segments 5–10 subserrate; frons with very fine median carina extending from interocular fovea nearly to the epistomal suture; vertex finely punctate; labrum finely granulate; eyes rounded, dark brown; ocular sinus 0.55 width of eye.

Prothorax. Subconical, pleura slightly concave; gibbosity with vaguely defined paired brown blotches; base lobed at middle; apex rounded.

Mesothorax and Metathorax. Scutellum small, triangular. Elytron evenly convex, slightly depressed in scutellar region; humerus prominent, with a fine, serrate, transverse carina connecting bases of striae 6 and 7, striae deep, narrow, strial punctures unisetose. Metepisternum finely microfoveolate. Hind coxa microfoveolate, setose, short area near trochanteral insertion with setose foveolae, small elongate lustrous area on anterior portion. Hind femur constricted basally and apically, expanded medially to about width of coxa; with very shallowly sulcate ventral margin and one small, sharp spine on medial margin of sulcus 0.25 from apex of femur ( Fig. 2 ); tibia sometimes with but usually without lateral, medial and ventral carinae; apex with five spinules, outer lateral spinule longer than others; claws lobed at base.

Abdomen. First abdominal sternum three times as long as second, with a carina 0.5 of the length of the sternum width near anterior margin; second, third and fourth sterna subequal; fifth slightly longer, deeply, broadly emarginate mesally; sterna 2–5 with a line of strong, black setae. Pygidium ovate and convex.

Size. Length (pronotum-elytra) 2.67 mm. Width 1.14 mm. Maximum thoracic depth 1.5 mm.

Genitalia. Median lobe with ventral valve U-shaped, with a group of setae flanking anterior portion, dorsal valve less sclerotized and U-shaped; armature of internal sac with two anterior masses of spines, a median mass of fine spines mixed with fine scale-shaped spines and two basal subtriangular sclerites ( Fig. 9 ). Lateral lobes cleft to 0.33 their length ( Fig. 10 ).

Female. Similar to male except first sternum without tuft of hairs; fifth sternum not emarginate, pygidium gibbous at apex.

Size. Length (pronotum-elytra) 2.37 mm. Width 1.47 mm. Maximum thoracic depth 1.5 mm.

Host Plants. Old records: Prosopis odorata Torr. and Frém. ( Kingsolver 1964:106; Kingsolver et al. 1977:115; Ward et al. 1977:6; Udayagiri and Wadhi 1989:95). P. pubescens Bentham ( Kingsolver 1964:106; Center and Johnson 1976:200; Ward et al. 1977:5; Johnson 1978:438; Johnson 1980:28; Udayagiri and Wadhi 1989:95)

Distribution. Old Records: USA (Arizona, California, Nevada, Utah) and Mexico ( Kingsolver 1964).

Discussion. This species is closely related to N. arizonensis , from which it can easily be distinguished by the uniformly gray tibiae, anteriorly placed prothoracic gibbosity ( Fig. 8 ), predominantly gray vestiture, the gibbosities are more markedly defined ( Fig. 8 ), and vaguely marked pygidium. The male genitalia of both are almost indistinguishable, except that N. gibbithorax has a group of setae flanking the anterior portion that are more numerous, the median mass of fine spinules is mixed with fine scale-shaped spines, and the two basal subtriangular sclerites are slightly more elongated.

There is considerable flux at present in the taxonomy of the genus Prosopis , but Prosopis pubescens is considered to be the valid name of this host, the screwbean mesquite. Some specialists in the genus advocate that there are only two species of mesquite (screwbeans and the others) and the rest of the 68 names are subspecies ( Hultine 2001). According to the available evidence, there is no interbreeding between the screwbean group and the others. Thus, N. gibbithorax and N. arizonensis follow taxonomic lines in their host preferences.

Figures

Fig. 7. Neltumius gibbithorax, male adult, dorsal view.

Figs. 1–2. Neltumius spp. 1) Antenna; 2) hind femur, medial view.

Figs. 9–10. Neltumius gibbithorax, male genitalia. 9) Median lobe, ventral view; 10) lateral lobes, ventral view.

Fig. 8. Neltumius gibbithorax, male adult, lateral view.