Tarsobaenus Leavengood, Pinkerton and Rifkind, 2022

Leavengood, John M., Pinkerton, Morgan G. & Rifkind, Jacques, 2022, Description of the new genus Tarsobaenus and three new species from Costa Rica (Coleoptera: Cleridae: Clerinae: Hydnocerini), Zootaxa 5138 (2), pp. 167-176 : 168-169

Tarsobaenus Leavengood, Pinkerton and Rifkind , new genus

http://zoobank.org/ urn:lsid:zoobank.org:act:AC3ABD70-7831-480D-AA90-1362CCE833B3

Type species: Tarsobaenus letourneauae, Leavengood, Pinkerton and Rifkind , new species. [male], here designated.

Description: Length: 5.05-5.35 mm. Body generally testaceous to orangish; antennomeres darkening apically; metathoracic macula black; other markings variable. Head: Slightly wider than humeri; surface smooth, impunctate, moderately covered in fine, long, pale, erect, semirecumbent setae; setae on eyes and posterolateral margin of head (behind eyes) longer; eyes prominent, distance across head at eyes distinctly wider than width at pronotal tubercles, sparsely clothed with fine, long, erect, pale setae. Antennae 10-segmented with distinct single-segmented club. Frons with two dorsally converging elongate depressions. Mouthparts with clypeus longitudinally subdivided; mandibles bifid, the right mandible dorsally excavated to receive the left; apical maxillary palpomeres securiform; apical labial palpomeres digitiform. Thorax: Pronotum widest at lateral angles but narrower than width of head, covered in long, erect, pale setae interspersed with short, pale, semirecumbent setae; pronotal disc shiny, sparsely, finely punctate; punctures obsolete on anterior and posterior pronotal collars; disc very convex, anterior collar strongly constricted, upturned at head, transverse impression complete, anterior fringe of short, pale, erect setae projecting over head; posterior collar abruptly curved upward at scutellar margin; posterior collar with fringe of long, pale, erect setae projecting over scutellum; scutellum with long, pale, erect setae projecting over base of elytral suture. Ventral prothorax sparsely covered with long, fine, suberect setae which become shorter, more recumbent towards middle; procoxal cavities open; mesothorax densely covered with white recumbent setae; metepisternum similarly but less densely hairy; metathorax sparely covered with long, pale, erect setae. Metathorax large, somewhat inflated; surface smooth, minutely granulate, shiny. Legs: Surface shiny, covered with long, fine, testaceous, erect setae of varying length; femora expanded, weakly laterally compressed, twice the width of tibia, slightly wider distally; metafemora extending well past apex of elytra when laid alongside; tibiae narrow, elongate, covered with long, fine, testaceous, erect setae of varying lengths, distal third with short fine, testaceous, semirecumbent setae, hind legs slightly longer but of similar form; tarsal claw deeply bifid (ungues present), tarsal puvillar formula 2-2-2 (3-3-3 considering a third on each tarsus that is much less developed). Wings: Elytra parallel to subparallel, widest at humeri, shiny, distinctly punctate with large, widely spaced punctures, apices barely covering abdomen, disc subflattened dorsoventrally, covered in long, fine, pale, erect and semirecumbent setae of varying lengths; internal margin of plica forming subulate excavation with distinct margin, ventral margin of excavation projecting inward more so than dorsal margin ( Figs. 5 , 10 , 15 ); lateral margins weakly serrulate, each serrulate denticle with single seta, serrulations strongest apically, more feeble anteriorly, obsolete in anterior third; strongly dehiscent in apical third beginning at posterior end of midelytral fascia where plicae broaden noticeably, apices distinctly tumid, serrate-spicular, independently rounded or subtruncate, interior angles of truncation negligibly serrate. Hindwing dusky-testaceous radiating from venation, apical 1/3-1/4 entirely cloudy black, not covered by elytra and obscuring apex of abdomen dorsally. Abdomen: weakly shiny, sparsely covered with long, erect, pale setae. Males (of letourneauae ) with sixth visible ventrite entire but deeply emarginate, modified with lateral, inward-curved clasper-like appendages fused at middle. Females with broad, gradual, smooth emargination on posterior margin of fifth sternite, sixth sternite divided longitudinally into two sclerites with widely-spaced, long, testaceous, subapical setae, dense apical fringe of shorter setae on each sclerite, apical tergite unmodified, but with pale setae of varying lengths, some apical and/or subapical setae quite long, curved.

Diagnosis: The species of Tarsobaenus are distinguished from other New World Hydnocerina by the broad, subulate form of the plical excavation along the sutural margin of the elytra, the lower margin of which is modified into a broad flattened flange reaching inward ( Figs. 5 , 10 , 15 ). When present in Phyllobaenus , Wolcottia and Isohydnocera , this plical structure is more elongate and shallow, typically tapering narrowly at either end. Furthermore, the protuberant eyes; convex, shiny pronotum; very large, coarse elytral punctures; serrulate apical elytral margins and especially the conspicuously large, shiny body also help to distinguish Tarsobaenus .

Discussion: Tarsal claw morphology, more specifically the presence and degree of development of the tarsal unguis, has been historically used to distinguish the three genera Phyllobaenus , Wolcottia and Isohydnocera . Like Phyllobaenus , Tarsobaenus has well developed, deeply notched tarsal ungues. The subulate plical modification at the approximate elytral dehiscence is more elongate and narrower in Phyllobaenus , although P. atriceps and P. subvittatus compare to the subulate broadness of Tarsobaenus . However, these Phyllobaenus species do not have tarsal ungues as pronounced as in species of Tarsobaenus . Still difficult to discern is the minute tibial spur formula (e.g., 1-2-2(?)), which may prove informative in inferring intergeneric relationships.

Biology: Members of Tarsobaenus are implicated in a remarkable symbiotic relationship with ants and their plant associates. Describing it as a “parasite of mutualism,” Letourneau (1990) observed a species of “ Phyllobaenus ” ( Tarsobaenus piper ) whose larvae inhabit the petiole chambers of Piper cenocladum C.DC. ( Piperaceae ), feeding on the plant-produced food bodies. Later, larvae of T. letourneauae were observed exhibiting the same behavior, as well as feeding on adult and immature Pheidole bicornis Forel ( Hymenoptera : Formicidae ). Both these species of Tarsobaenus appear to chemically mimic their ant prey in order to induce food body production in the plant, which is normally a species-specific response to the presence of the ants ( Letourneau, 1990, 1993; Letourneau and Dyer, 1998; Dyer and Letourneau, 1999, 2003; Letourneau et al., 2004).

Figures

FIGURES 1–6. Tarsobaenus letourneauae, n. sp. (paratypes): 1—dorsal habitus; 2—head; 3—male, ventral abdomen; 4—female, ventral abdomen; 5—elytral plica; 6—lateral habitus.

FIGURES 7–11. Tarsobaenus piper, n. sp. (holotype, paratype): 7—holotype, dorsal habitus; 8—head; 9—paratype, dorsal habitus; 10—elytral plica; 11—lateral habitus.

FIGURES 12–16. Tarsobaenus hansoni, n. sp. (holotype, paratype): 12—holotype, dorsal habitus; 13—head; 14—paratype, dorsal habitus; 15—elytral plica; 16—lateral habitus.