Leptocera plax, Buck & Marshall, 2009

Buck, Matthias & Marshall, Stephen A., 2009, Revision of New World Leptocera Olivier (Diptera, Sphaeroceridae), Zootaxa 2039 (1), pp. 1-139 : 119-121

Leptocera plax species group

Species included. L. plax sp.n., L. posteronitens sp.n., L. tapanti sp.n.

Description. Body length 2.0–4.0 mm. Body dark brown, anterior part of frons, ocellar triangle in front of ocellar tubercle, inner surface of pedicel and first flagellomere, and palpus more or less dark reddish to yellowish brown. Apicomedial part of fore coxa (usually), inner surface of fore femoral apex (usually), apical part of mid tibia as well as mid and hind tarsi paler brown. Wing moderately infuscated, especially along anterior margin. Halter white, stem whitish brown. Lower orbital bristle 0.8–0.9x as long as upper one. Facial tubercle more prominent and antennae farther apart than usual. No additional setulae on orbit behind upper orbital bristle. Palpus slender. Arista long, long-pubescent (plumosity longer than in other species groups). Scutum thinly pruinose and quite shining, posterolaterally (i.e., lateral of dorsocentral lines and posterior to presutural intra-alar bristle) with bluish reflections. Scutellum velvety with weak, dark bluish reflections except for subshining anterior margin and areas around sockets of bristles. Scutum with 4–5 dorsocentral bristles, fifth one from behind, if differentiated, small; enlarged paramedian acrostichals large, longest one usually as long as upper orbital bristle, arranged in 2–3 pairs plus 1(–2) unpaired bristle(s) posteriorly on one side; prescutellar acrostichals enlarged, in L. tapanti sp.n. often quite long. Prosternum with (0–)1–2(–3) setulae on each side of midline. Fore tarsus with middle tarsomeres slightly wider in male than in female. Mid tibia with lowermost bristle of proximal posterodorsal series short, 0.5–0.6x as long as lowermost bristle of anterodorsal row (in very small specimens sometimes longer); bristle above distal dorsal short, usually shorter than corresponding bristle above distal anterodorsal; posteroapical bristles short, ventral one absent in L. plax sp.n. Bristles on dorsal surface of hind tibia relatively short, those of distal half longer and slightly raised to semi-erect, no well-differentiated preapical bristle.

Male terminalia: Sternite 5 lacking densely microtrichose posteromedial field (this area either bare or beset with small teeth similar to marginal scales); posterior margin with very stout, tooth-like, enlarged scales (lateral ones either largest or the only ones present). Sternite 8 separate from epandrium in L. plax sp.n., fused in L. tapanti sp.n. Surstylus of characteristic and unusual shape: Anterior section with very long bristles on anterior portion of ventral lobe, posteriorly with 3–4 long bristles (instead of the usual 1–2). Posterior section of surstylus divided into plate like basal portion ( Figs. 280 , 290 : pssb; fused to epandrium in L. tapanti sp.n.), and a narrow, finger-like distal portion ( Figs. 281 , 291 : pssd), which runs parallel (and very close) to the distal part of the postgonite (the two are of similar length and strength and are easily confused with each other under low magnification). The basal and distal portions are connected by a very narrow strand of sclerotization ( Figs. 282 , 292 : pssc) and are otherwise broadly removed from each other. Cercus with long bristles, simple or with medial process ( L. plax sp.n.). Postgonite angulate but without distinct posterobasal notch, shanks short ( Figs. 298, 302 ).

Female terminalia: Tergite 7 very short, shorter medially than laterally. Sternite 7 with hind margin nearly straight or strongly produced medially. Halves of tergite 8 large, valve-like; together with fused tergite 10 + cerci completely covering genital opening and anus in resting position. Sternite 8 wide, more or less angulate laterally, posterolateral lobes subtriangular; one pair of setulae inserted much more anteriorly than the other pair (in other Leptocera the two pairs are usually inserted very close to each other). Fused tergite 10 + cerci large, forming a dark brown, strongly sclerotized plate bearing one pair of relatively long bristles and several short hairs. Spermathecae spherical with numerous spicules near base, surface finely striate.

Taxonomy. The species of this group are fairly uniform externally but show distinct differences in the male and female terminalia. The most important external character is the number of posteroapical bristles on the mid tibia.

Biogeography. The L. plax group is restricted to Central and South America, predominantly the cloud forest zone (700–2,200 m).

Phylogeny. The L. plax group is newly erected for a well defined clade of three Neotropical species. Defining characters include: Male sternite 5 lacking posteromedial field of dense microtrichia, its posterior margin with lateral scales enlarged, stout and tooth-like; anterior section of surstylus with 1–2 rows of very long bristles; posterior section of surstylus with basal and distal portions removed from each other and only narrowly connected; distal portion of posterior section of surstylus lacking large bristles, slender, oriented parallel and close to distal part of postgonite (both similar in shape and length); female tergite 7 very short, shortened medially; fused female tergite 10 + cerci forming a dark, strongly sclerotized plate.

Biology and habitat. As far as is known the species of this group inhabit montane tropical forests. The larval habitat is unknown but one species ( L. tapanti sp.n.) is strongly attracted to decaying vegetation. Within just a few hours the senior author was able to obtain nearly 300 specimens of this species from the foliage of a recently fallen tree at Monteverde , Costa Rica (using a sweep net and yellow pan traps) . Two smaller series of the same species were collected in pan traps on kitchen compost. Only one specimen (collected by E. Barr in Monteverde) was obtained from a dung trap. Leptocera plax sp.n. also appears to be attracted to dung to some degree. We strongly suspect that L. tapanti sp.n. breeds in the decaying foliage of fallen trees (and similar substrates), the other two species will probably show similar biologies. Unexplained is the greatly biased sex ratio in many samples, e.g., L. tapanti sp.n.: 206 ♂♂, 88 ♀♀ from treefall (Monteverde, Costa Rica), 4 ♂♂, 32 ♀♀ from malaise trap (16 km SSE La Virgen, Costa Rica) .

Figures

FIGURES 280–286. Leptocera plax sp.n. (Ecuador). Male terminalia (phallus and postgonites omitted): (280) lateral; (281) posterior; (282) ventral; (283) sternite 5. Female terminalia: (284) dorsal; (285) spermathecae; (286) ventral. aps—anterior process of anterior section of surstylus; ce—cercus; cp—finger-like process of cercus; ep—epandrium; ha—hypandrial apodeme; hy—hypandrium; pa—phallapodeme; pssb—posterior section of surstylus, basal part; pssc—ditto, connection between basal and distal part; pssd—ditto, distal part; S—sternite; sc—enlarged scales; se—subepandrial sclerite; T—tergite (female tergite 8 divided into two halves); vls—ventral lobe of anterior section of surstylus.

FIGURES 290–296. Leptocera tapanti sp.n. (Costa Rica). Male terminalia (phallus and postgonites omitted): (290) lateral; (291) posterior; (292) ventral, distal part of posterior section of surstylus omitted; (293) sternite 5. Female terminalia: (294) dorsal; (295) spermathecae; (296) ventral. aps—anterior process of anterior section of surstylus; ce—cercus; ep—epandrium; pssb—posterior section of surstylus, basal part (fused with epandrium); pssc—ditto, connection between basal and distal part; pssd—ditto, distal part; vls—ventral lobe of anterior section of surstylus.

FIGURES 297–304. Aedeagal complex and subepandrial sclerite of Leptocera plax group. Leptocera plax sp.n. (Ecuador): (297) subepandrial sclerite and posterior section of surstylus, posterior; (298) aedeagal complex, lateral; (299) ditto, dorsal; (300) ditto, posterior; (301) ditto, anterior. Leptocera tapanti sp.n. (Costa Rica), aedeagal complex: (302) lateral; (303) dorsal; (304) anterior. bcp—basal connection between postgonites, bp—basiphallus, dp—distiphallus, ea—ejaculatory apodeme, pa—phallapodeme, pg—postgonites, pss—posterior section of surstylus, se—subepandrial sclerite.