Macrosiagon gracilis Manfrini de Brewer 1966:40

Falin, Zachary H., 2004, Revision of Three New World Macrosiagon Hentz Species (Coleoptera: Ripiphoridae: Ripiphorinae) with a Discussion of Phylogenetic Relationships within the Macrosiagonini, The Coleopterists Bulletin 58 (1), pp. 1-19 : 3-8

Macrosiagon gracilis Manfrini de Brewer 1966:40 .

Description, Male. General body form typical of Macrosiagon , although smaller, more delicate, and not as heavily sclerotized as most species of this genus ( Fig. 1 ). Overall length from frons to elytral apices 3.4–7.6 mm, (avg. 5.6 mm, n ¼ 12). Head smaller, vertex much less elevated and elytra less acuminate than typical. Color variable; head yellow with vertex brown, the dark coloration extending anteriorly along the inner margins of the eyes and as a central truncate stripe nearly to antennal bases in some specimens. Pronotum yellow with broad, longitudinal median brown stripe, some specimens with yellow stripe within brown band. Elytra entirely brown or brownish-yellow with brown apices. Color of thorax, legs and abdomen variable, generally yellow with varying degrees of brown; hind legs brown and abdomen yellow with brownish pygidium in most specimens. Wings fuscous.

Head small; vertex convex antero-posteriorly, transversely planar, shining, shallowly punctate, punctures increasing in density towards dorsal margin of eyes and posterior margin of vertex. Punctures with slight to moderate transverse appearance in most specimens. Area of frons from base of antennae to frontoclypeal margin transversely concave ( Fig. 1 ), giving the appearance of a transverse ridge between bases of antennae, particularly in smaller specimens. Area immediately dorsal to frontoclypeal margin strongly and regularly punctate, otherwise frons lightly and irregularly punctate. Frontoclypeal margin broadly emarginate. Labrum visible beneath frontoclypeus in some specimens, densely and relatively strongly punctate, ventral margin somewhat variable, broadly rounded to nearly truncate, with a fringe of long, downward facing setae.

Antennae typical of males of the genus, 11-segmented, antennomeres I and II simple, subcylindrical. Length of antennomere I 2.5 3 that of II. Antennomeres III–X subequal, cylindrical, biramous, rami threadlike, cylindrical with scattered sensilla, each sensillum slightly longer than width of ramus. Antennomere XI simple, similar in appearance to rami of previous segments, slightly compressed distally.

Pronotum subconical; posterior angles sharp, reaching the posterior margin of the mesepimeron in most specimens. Lateral aspect of pronotum typical of genus, without margins, basal half narrowed dorso-ventrally and strongly expanding anteriorly. Ventral margin of lateral aspect of pronotum flat for approximately 1/2 its length, then uniformly arched anteriorly. Posterior lobe of pronotum a thin, obtusely triangular flange covering the scutellum in some specimens, revealing the posterior apex of scutellum in others. Pronotal disc regularly convex, smooth and shining, its surface finely, densely and regularly punctate, with recumbent setae. Prosternum a flattened, acutely pointed triangular projection extending approximately 3/4 length of procoxae, separating them.

Lateral and ventral aspects of thorax more or less typical of genus, though more weakly and irregularly punctate than that of most species; punctures variable, though less strong and less dense than pronotum. Lateral aspect of meso- and metathorax remarkably planar, not visible from above as in some species of the genus. Mesosternum similar in form to prosternum except broader, not as acute, and lying more ventral to mesocoxae, not effectively separating them. Metasternum broad, expanded, typical of genus.

Legs typical, densely punctate and setose; ventral surface of apical 1/4 of profemora excavated with row of dense setae; apices of all tibiae with two ventral spurs. Tarsi 5-5-4, all tarsomeres more or less cylindrical, second metatarsomere longer than third ( Fig. 3 ). Claws typical; long, curved, laterally compressed and finely bifid at apex.

Elytra subparallel along the lateral margins, medial margin strongly divergent only in apical 1/6; apices relatively blunt for genus. Elytra more or less uniformly convex, a slight longitudinal depression visible in basal 2/ 3 in some specimens. Punctation and setation similar to that of pronotum.

Abdomen typical of genus, punctation fine, regularly spaced, of medium density, with recumbent setae. Abdominal segment IX ( Fig. 7a–c ) trilobed dorsally, median lobe overlapped dorsally by lateral lobes, median lobe subhemispherical and well sclerotized throughout; lateral lobes also subhemispherical, extending antero-ventrally forming a stirrup-like structure, anterior apices fused; the three dorsal lobes with fine, scattered setae. Ventral lobe of segment IX relatively well sclerotized, convex ventrally, deeply emarginate, with scattered setae at the posterior apices, produced anteriorly into a flattened, elongate stirrup-like structure.

Gonoforceps ( Fig. 9a, b ) large, asymmetrical, tightly articulated to dorsal aspect of body of tegmen; one forcep resembling a laterally-projecting thick, curved tooth or hook, the other a dorsoventrally aligned irregular, broad hook. Gonoforceps with scattered setae, longest and densest in the ventral aspect. Tegmen resembles a curved plate surrounding median lobe, also asymmetrical, anterior aspect curving ventrally and to the side. Ventral baculi fused into an irregular, v-shaped sclerite through which median lobe passes. Median lobe relatively broad, gently dorsally arched, approximately 1.5 3 length of tegmen, with blunt, slightly ventrally curved apical tooth.

Female. Externally identical to male except for antennae. Antennomeres I and II as in male; antennomeres III–X subequal, cylindrical, uniramous; rami cylindrical, slightly smaller in diameter than associated antennomeres, acute at apex, nearly 2 3 length of antennomere of origination, appearing longer and more broadly spaced than typical for genus. Most sensillae much shorter than in male, recumbent, interspersed with longer, more erect sensillae.

Immature Stages. Individuals of M. gracilis have been reared from cells of Megalopta species ( Hymenoptera : Halictidae , see below), although no immature stages have been preserved or described.

Type Material. Manfini de Brewer (1966) described Macrosiagon gracilis from one male and one female specimen, both collected in Argentina. The holotype male is labelled as follows: ‘‘R.A. Catamarca, El Alto, 1,000 m, 4-XII-1958, Comisión Lillo’’ handwriting/ ‘‘Holotypo’’ typeface on red paper/ ‘‘ Macrosiagon gracilis Brewer , det. M. Brewer’’ handwriting/ ‘‘Colección Inst.-Fund. M. Lillo, (4000) S. M. Tucuman, Tucuman, Argentina’’ typeface. The female allotype (¼ paratype) is labelled as follows: ‘‘R.A. Catamarca, El Rodeo, 1,500 m, 28-I-1959, R. Golbach’’ handwriting/ ‘‘Allotypo’’ typeface on red paper/ ‘‘ Macrosiagon gracilis Brewer , det. M. Brewer’’ handwriting/ ‘‘Colección Inst.-Fund. M. Lillo, (4000) S. M. Tucuman, Tucuman, Argentina’’ typeface. The left middle leg of the holotype is intact, as is the right hind leg to the apex of the tibia; the other legs are missing at the coxae. The right antenna of the holotype lacks antennomeres III–XI and there is some damage to the abdomen, otherwise the specimen is whole. Only the coxae and one trochanter are left of the front legs of the allotype, and one middle and one hind leg is likewise missing. Both specimens are deposited at the IMLA.

(c) lateral view. 7) M. gracilis ; 8) M. mutilata .

Other Material Examined. 15 specimens total. ARGENTINA : 1 female, Jujuy [Prov.], Posta Lozano , 15 to 17-XII-1967, C.C. Porter [coll.] ( MCZC) ; 1 male, Prov. Salta, Cerrillos , INTA, 5 to 9-II-1982, H. and A. Howden [colls.] ( CMNC) ; 1 female (disarticulated) and 2 specimens (sex undetermined), [at] Miami [in quarantine], [from] Argentina , 8-IV-1969, ‘‘with bromeliads,’’ R.J. Reasoner [coll.] ( USNM). BOLIVIA : 1 female and 1 specimen (sex undetermined), [ Cochabomba Dept. ,] Cochabamba, 9-X- 1948, Pena [coll.] ( CASC). BRAZIL : 1 male, Nova Teutonia, Sta. Catharina , 27-X- 1944, 300– 500 ft elev., F. Plaumann [coll.] ( FMNH) ; 1 specimen (sex undetermined), Brasilia , Capta, D. Swainson [coll.] ( BMNH). COSTA RICA : 1 male, Guan [acaste Prov.], 3 km SE R. Naranjo, 1 to 10-VIII-1992, F.D. Parker [coll.] ( EMUS). PANAMA : 1 specimen (sex undetermined), Canal Zone, 5.0 mi NW Gamboa, 09 8 10 9 N

79 8 45 9 W, 30-III- 1976, 100 m elev., ‘‘canopy fogging experiment in Luehea seemani [,] pyrethrin fog,’’ Montgomery and Lubin coll. ( USNM); 4 females, Canal Zone, Isla Barro Colorado, 09 8 09 9 N 79 8 51 9 W, 1 to 15-VII-1999, W.T. Wcislo [coll.], reared from cells of Megalopta genalis (Halictidae) ( SEMC).

Distribution. Apart from the holotype male and single allotype female, the above specimens are the only representatives of this species known to the author. It appears that this species is widespread in South America at a variety of elevations and reaches at least as far north as central Costa Rica. Additional collections of this species are necessary to more precisely determine its range and habitat preferences.

Bionomics. Macrosiagon gracilis has been reared from the nests of the nocturnal halictid bee Megalopta genalis Meade-Waldo and Megalopta ecuadoria Friese in Panama ( Falin et al. 2001), although its size variation and distributional range suggest that it uses more than these two host species. It is interesting to note that a Panamanian specimen was collected by pyrethrin fogging tree canopies and that three Argentinian specimens were apparently collected during quarantine in Miami ‘‘with bromeliads.’’ This, along with the fact that the two confirmed host species nest in dead wood suspended off of the ground (Wcislo, Arneson and Roubik, forthcoming publication) suggests that M. gracilis does not frequent the lower levels of the forest understory, possibly explaining its relative rarity in collections. No other members of the genus have been collected under these circumstances.

Diagnostic Characters. Macrosiagon gracilis is easily distinguished from all other Macrosiagon species by the combination of its 2-2-2 tibial spur formula and the fact that the second metatarsomere is cylindrical (not dorsally flattened) and longer than the third. Further, the concave nature of the frons and the appearance of a frontal ridge between the antennal bases is unique for the genus and is reminiscent, albeit in a less drastic form, of the dorso-ventrally ‘‘pinched’’ frons found in the genus Metoecus . It can be further separated from the other members of the vittata species group by being more weakly sclerotized, more parallel sided and by the relatively long, slender antennal rami of the females.

Comments. As is common for members of this genus, M. gracilis varies considerably in size and coloration, and appears to have a relatively large, disparate range. Nonetheless, the diagnostic characters easily separate it from all other Macrosiagon . Apart from size and coloration, there is some variation in the density and coarseness of punctation, particularly on the elytra; the single specimen from ‘‘Brasilia, Capta’’ is less densely and less strongly punctured on the elytra than the other specimens. It is possible that this variant represents an independent species, though more specimens need to be examined to make this determination.

In the original description, Manfrini de Brewer (1966) notes a difference in coloration of the pronotum in the one male and one female specimen she examined. Given the additional specimens I have examined, these differences do not appear to be significant. Manfrini de Brewer also states that the elytra are black in this species. While this is true for most specimens, the examples collected in Panama and the one from ‘‘Brasilia, Capta’’ have elytra brownish-yellow with brownish apices. Manfrini de Brewer (1966:43) also remarks that the elytra of M. gracilis are ‘‘much shorter than the body....’’ This is somewhat subjective as the length of the body depends on the relative extension of the telescopic abdomen at the time of preservation. The elytra of the specimens I have examined extend nearly to the tip of the abdomen in most cases and are not significantly shorter than those of other Macrosiagon species. Finally, Manfrini de Brewer notes that abominal segment IX in the male of M. gracilis is similar to that of M. octomaculata (Gerstaecker) , which is itself distinct from that of M. excavata (Champion) and M. flavipennis (LeConte) . It is unclear from her descriptions and illustrations exactly what she meant by this, though it appears that the median dorsal lobe of abdominal segment IX is missing from her illustrations of M. gracilis and M. octomaculata . My own dissections confirm the existence of the median lobe in both these species, albeit abdominal segment IX in the former is somewhat less wellsclerotized than in most other species in this genus.

Figures

Figs. 1–2. Macrosiagon spp., females, lateral habitus. 1) M. gracilis; 2) M. mutilata.

Figs. 3–4. Macrosiagon spp., metatarsus, dorsal view. 3) M. gracilis; 4) M. mutilata.

Figs. 7–8. Macrosiagon spp., male abdominal segment IX; (a) dorsal view, (b) ventral view,

Figs. 9–10. Macrosiagon spp., male genitalia with median lobe in situ; (a) dorsal view, (b) ventral view. 9) M. gracilis; 10) M. mutilata.