Elateriformia (Coleoptera)

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J. F. Lawrence, A. M. Hastings, M. J. Dallwitz, T. A. Paine and E. J. Zurcher

THROSCIDAE

(= Trixagidae).

Classification. Polyphaga: Elateriformia.

Distribution. Throscidae occur in most parts of the world, but have not been reported from New Zealand.

Biogeographic regions: Nearctic, Palearctic, Neotropical, Afrotropical, Oriental, Australian.

Biology. Throscid larvae are often taken in the soil, where they feed on ectomycorrhizal fungi on the roots of various trees; however some have been collected in rotten conifer wood and grass tufts. Neocrowsonia adults have been collected in the nests of a termite.

Notes. Throscidae is used here in a restricted sense, excluding both Thylacosterninae and Lissominae; however Muona (1995) made a case for the monophyly of Throscidae in the sense of Crowson (1951, 1955) either as a separate family of Elateroidea or as a clade within Elateridae.

References

Burakowski, B. 1973. Immature stages and biology of Drapetes guttatus (Piller) (Coleoptera, Lissomidae). Annales Zoologici (Warszawa) 30: 335–347.

Burakowski, B. 1975b. Development, distribution and habits of Trixagus dermestoides (L.), with notes on the Throscidae and Lissomidae (Coleoptera, Elateroidea). Annales Zoologici (Warszawa) 32: 375–405.

Cobos, A. 1961. Sobre la posicion sistematica del genero Potergus Bonvouloir y revision de las categorias supragenericas de la familia Throscidae (Coleoptera). Bulletin de l'Institut Royal des Sciences Naturelles de Belgique 37(35): 1–6.

Cobos, A. 1967. Estudios sobre Throscidae, II (Col. Sternoxia). Eos 42 (1966): 311–351.

Crowson, R. A. 1951. The classification of the families of British Coleoptera (part). Entomologist's Monthly Magazine 87: 117–128 (Buprestoidea, Elateroidea, Cantharoidea).

Crowson, R. A. 1955. The Natural Classification of the Families of Coleoptera. Nathaniel Lloyd, London, 187 pp.

Johnson, P. J. 2000. 62. Throscidae. IN: R. H. Arnett, Jr., Jr. and M. C. Thomas (eds.), American Beetles. CRC Press, Gainesville, Florida (in press).

Kistner, D. H. and F. A. Abdel-Galil 1986. A new genus and species of termitophilous Throacidae from South Africa (Coleoptera). Sociobiology 12: 305–313.

Leseigneur, L. 1995. Statut actuel des genres Trixagus Kugelann, 1794, et Throscus Latreille, 1796. Désignation des lectotypes des espèces paléarctiques de H. Bonvouloir (Coleoptera, Throscidae). Bulletin de la Société Entomologique de France 100: 347–359.

Lohse, G. A. 1979. 37. Familie: Throscidae, pp. 201–203. IN: H. Freude, K. W. Harde and G. A. Lohse (eds.), Die Käfer Mitteleuropas. Band 6. Diversicornia. Goecke & Evers, Krefeld.

Muona, J. 1993. Eucnemidae and Throscidae from Baltic amber (Coleoptera). Entomologische Blätter für Biologie und Systematik der Käfer, Berlin 89: 15–45.

Muona, J. 1995. The phylogeny of Elateroidea (Coleoptera), or which tree is best today? Cladistics 11: 317–341.

Schenkling, S. 1928. Pars 96. Melasidae. IN: S. Schenkling (ed.), Coleopterorum Catalogus. W. Junk, Berlin, 110 pp.

Schenkling, S. 1928. Pars 101. Throscidae, Cerophytidae, Perothopidae. IN: S. Schenkling (ed.), Coleopterorum Catalogus. W. Junk, Berlin, 30 pp.

Yensen, E. 1975. A review of the genus Pactopus LeConte (Coleoptera: Throscidae). Coleopterists Bulletin 29: 87–91.

Yensen, E. 1975. A revision of the North American species of Trixagus Kugelann (Coleoptera: Throscidae). Transactions of the American Entomological Society 101: 125–166.

General appearance. Total length 1.5–6 mm. Ratio of body length to greatest body width 1.9–3.42. Body strongly flattened, or slightly flattened to moderately convex, or strongly convex. Sides of body not evenly curved. Body not capable of conglobation (rolling into a ball). Upper surfaces of body glabrous or subglabrous, or clothed with distinct hairs, setae or scales. Vestiture of upper surfaces not including stiff, erect, dark bristles; not including scales or scale-like setae. Upper surfaces of body without deep foveae. Prothorax, metathorax and-or abdomen without extrusible glands. Underside of body without hydrofuge surface(s).

Head. Ratio of head length to its greatest width (excluding eyes) 1 or less. Head width just behind eyes not distinctly greater than prothoracic width. Head not or slightly declined, or moderately to strongly declined; not entirely concealed from above by pronotum; without elongate rostrum; not abruptly constricted posteriorly. Temples absent or not closely adpressed to prothorax; absent. Transverse occipital ridge or carina absent, or present. Occiput without stridulatory file. Longitudinal axis of head (from occipital foramen to mouth cavity) inclined at an angle of less than 45 degrees, or inclined at an angle of 45 to 90 degrees. Frontal region not to moderately, gradually declined, or strongly deflexed, vertical or inflexed from behind eyes. Occipital region without median longitudinal groove or line (endocarina), or with median longitudinal groove or line (endocarina). Frontal region without median groove or line (endocarina), or with median groove or line (endocarina). Head without ocelli.

Compound eyes present, or absent. Eyes not or only slightly protuberant. Vertical diameter of eye less than 2 times horizontal diameter. Eyes finely facetted; without interfacetal setae. Ommatidium of the exocone type. Eye entire. Anterior or mesal edge of eye not or only barely emarginate, or shallowly emarginate or slightly divided by canthus, or deeply emarginate or strongly divided by canthus. Posterior edge of eye not or barely emarginate.

Antennal insertions exposed from above, or concealed from above; moderately to widely separated, or narrowly separated. Antennae not borne on raised tubercles. Antennal insertions flush with head capsule or raised, not in fossae, or countersunk so that they lie within saucer-like fossae. Subantennal groove or cavity on head absent or very weakly developed, or well developed. Frontoclypeal suture absent or incomplete. Clypeus not laterally emarginate. Anterior edge of clypeus or clypeolabrum straight to convex, or deeply emarginate or excavate. Mouth cavity anteriorly or anteroventrally oriented, or ventrally or posteroventrally oriented. Pregular area without laterally opening cavities. Head ventrally without paired subgenal ridges, or with paired subgenal ridges. Head without anteriorly-projecting genal processes. Gular sutures widely separated or absent. Corporotentorium narrow, or incomplete or absent; without median process. Cervical sclerites present.

Antennae. Number of antennomeres 8–9, or 11. Antennae when posteriorly extended not reaching middle of prothorax, or reaching beyond middle of prothorax but not middle of elytra. Antennae filiform, or moniliform, or incrassate or clavate, or capitate. Antennomeres 3, 4 or 5 to 10 without or with single rami (uniramose). Antennae at least partly pubescent or with obvious modifications. Antennal modifications beginning on antennomere 5 or beyond. First antennomere (scape) less than 3 times as long as 2nd (pedicel), or more than 3 times as long as 2nd (pedicel). Antenna not geniculate; without apical club, or with weak apical club, or with strong apical club. Antennal club 3-segmented, or with 6 or more segments; not 5-segmented or with 2nd segment subequal to or larger than 1st; loose, or compact; not lamellate; not or slightly serrate, or strongly serrate or pectinate, or flabellate; not cupuliform; not or slightly flattened; not preceded by a cupule.

Mouthparts. Labrum at least partly visible, or concealed beneath clypeus or apparently absent; free, membranous or separated by suture, or partly or completely fused to clypeus or frontoclypeus, without or with incomplete suture. Major portion of labrum strongly transverse. Apex of labrum subtruncate to slightly convex, or strongly convex, narrowly rounded or acute, or trilobed or with several lobes or teeth. Labrum moderately to heavily sclerotized, except at base and-or apex. Mouthparts not forming a piercing or sucking tube. Mandibles present. Mandible short and broad. Mandibular apex not or slightly and gradually curved mesally, or moderately to strongly, gradually curved mesally; unidentate, truncate or rounded; subacute, bidentate or multidentate. Dorsal part of mandible without tubercle; without setose cavity. Mandible moderately to strongly, more or less evenly sclerotized or pigmented; visible in lateral view. Incisor edge of mandible simple, or with single tooth. Mandible with reduced mola, or without mola; with reduced prostheca, or without prostheca. Prostheca absent or without articulated, sclerotized process. Inner basal angle of mandible without pubescent process. Maxilla with distinct galea and lacinia, or with single apical lobe. Maxillary lobe(s) not stylet-like. Apex of galea or maxillary lobe densely setose or spinose, or without or with few setae or spines; without heavily sclerotized teeth or hooks. Lacinia without hook(s) or spine(s). Apical maxillary palpomere cylindrical to fusiform, or slightly expanded and truncate to subtriangular; at least as wide as or longer than preapical one. Maxillary palp without complex palp organ. Apical labial palpomere cylindrical to fusiform, or slightly to strongly expanded apically. Ligula undivided or finely cleft, or shallowly to moderately emarginate, or indistinct or absent.

Prothorax. Ratio of pronotal length to greatest pronotal width 0.5–0.93. Prothorax widest posteriorly. Sides of prothorax more or less straight, or moderately to strongly curved, or sinuate. Prothorax not laterally compressed to form cavities for legs. Sides of prothorax not or slightly explanate, or moderately to strongly, horizontally explanate, or moderately to strongly, obliquely or vertically explanate. Base of prothorax not or slightly narrower than elytral bases. Greatest prothoracic width not or slightly narrower than greatest elytral width. Lateral pronotal carinae complete, or incomplete; simple; visible for their entire lengths from above, or not visible for their entire length from above; without a raised margin, or with a raised margin or narrow bead. Lateral portion of prothorax without deep pit. Pronotum without anterolateral callosities. Anterior angles of pronotum absent or not produced forward; absent, right or rounded, not produced. Posterior angles of pronotum obtuse or right, or moderately to strongly acute; not produced and acute, or strongly produced and narrowly acute. Posterior edge of pronotum more or less straight or evenly rounded, or distinctly sinuate or variously lobed; simple; not or vaguely margined. Discal carinae of pronotum absent, or located on posterior angles only. Pronotal disc without paired basal impressions. Pronotum without median longitudinal groove or line. Anterior edge of pronotum simple, without margin. Hypomeron without pit.

Anterior portion of prosternum at midline shorter than prosternal process, or longer than prosternal process. Lateral portion of prosternum in front of coxae longer than mid length of procoxal cavity. Anterior edge of prosternum distinctly produced forming chin piece. Prosternum in front of coxae flat to moderately convex, or strongly convex without carina. Prosternum in front of coxae without paired lines or carinae, or with paired lines or carinae. Anterior edge of prosternum without margin; without mesal excavation. Anterolateral or ventrolateral portions of prothorax without cavities or grooves, or with broad cavities, or with narrow grooves. Prothoracic cavities absent, or external, open anteriorly, not visible from above. Prothoracic grooves absent, or longitudinal, below lateral edges of prothorax, or longitudinal or oblique, elsewhere on hypomera or prosternum. Prosternal process complete, or incomplete, or absent; narrowed apically, or parallel-sided, or gradually expanded and then narrowed; flat, concave, or only slightly elevated or curved behind coxae, or strongly elevated and curved dorsally behind coxae, or slightly to strongly elevated but not curved behind; not extending to mesoventrite, or moderately to strongly overlapping mesoventrite, or concealing most or all of mesoventrite. Apex of prosternal process acute or narrowly rounded, or broadly rounded, angulate or truncate. Prosternal process without transverse groove. Accessory (mesal) procoxal articulation absent. Ventral portion of prothorax on each side with notosternal suture only. Propleuron not extending to anterior edge of prothorax. Propleuron or pleurotrochantin not extending behind coxa. Procoxae not or slightly projecting below prosternum, or projecting well below prosternum. Procoxa without or with short concealed lateral extension. Procoxal cavities present, procoxae countersunk. Procoxal cavity circular or longer than wide. Procoxal cavities at middle contiguous, or moderately to widely separated. Procoxal cavities externally open; broadly open. Postcoxal projection absent or very short, or moderately long but not meeting prosternal process. Procoxal cavities without narrow lateral extensions. Procoxal cavities internally open. Prothoracic trochantin or pleurotrochantin completely concealed or absent. Promesothoracic clicking mechanism absent, or present.

Elytra. Elytra present. Ratio of elytral length to greatest elytral width 0.66–2.52. Ratio of elytral length to pronotal length 1.05–4. Elytra apunctate, irregularly punctate, or with 5 or fewer distinct puncture rows or striae, or with more than 5 distinct puncture rows; without scutellary striole. Number elytral puncture rows or striae 9. Sutural stria absent or not deeply impressed near apex. Abdominal tergites exposed by elytra none or apex of 1, or at least 2 but less than 3, or 3 or more. Exposed abdominal segments more or less flexible. Elytral apices meeting or almost meeting at the suture, or independently rounded or acute and separated by broad gap. Elytral suture not deflected near apex. Elytral apex without internal interlocking tongue. Epipleuron absent or incomplete, or complete; not or gradually narrowed, or abruptly narrowed or excavated. Lateral edge of elytron straight or weakly sinuate.

Pterothorax. Scutellum well developed, or absent or not visible; abruptly elevated; anteriorly simple; posteriorly narrowly rounded or acute, or broadly rounded or obtusely angulate. Mesoscutum without stridulatory file. Mesoventrite without paired procoxal rests, or with paired procoxal rests. Paired mesoventral procoxal rests absent, horizontal or slightly oblique, or moderately to strongly oblique. Anterior edge of mesoventrite without prosternal rest, or with median prosternal rest. Mesoventrite not divided by longitudinal groove or discrimen. Anterior edge of mesoventrite at midline on same plane as metaventrite, or on different plane than metaventrite. Mesoventral cavity absent, or moderately to very large and deep. Mesocoxa not conical and projecting. Mesocoxal cavities present, mesocoxae countersunk. Mesocoxal cavities at middle moderately to widely separated. Mesocoxae separated by more than shortest diameter of coxal cavity. Mesocoxal cavities circular to slightly transverse; not or slightly oblique. Mesoventrite separated by complete sutures from mesepisterna, or partly or completely fused to mesepisterna. Mesepisterna distinctly separated at midline; without deep pockets. Mesepimeron not visible from above. Mesocoxal cavities open laterally; not partly closed by metepisterna. Mesoventral process extending at least to middle of mesocoxal cavity. Mesometaventral junction a straight line, or an anteriorly curved, angulate or acute line, or absent due to fusion. Mesoventral and metaventral processes at midline separated by gap, groove, or suture, or solidly fused or separated at most by weakly impressed line. Accessory (mesal) mesocoxal articulation absent.

Metaventral discrimen or median line moderately to very long, or absent. Paired postcoxal lines of metaventrite absent, or present. Postcoxal lines of metaventrite absent, or straight or slightly, mesally curved. Metaventrite longer than first abdominal ventrite, or not longer than first abdominal ventrite. Postcoxal pits of metaventrite absent. Metaventrite flat to slightly convex, or moderately to strongly convex. Transverse groove of metaventrite absent. Anterior edge of metaventrite without transverse carina between mesocoxal cavities. Exposed portion of metepisternum very long and narrow or absent. Metacoxae contiguous or narrowly separated; separated by less than longest coxal diameter; not extending laterally to meet elytra or sides of body, or extending laterally to meet elytra or sides of body; completely separated from metaventrite by suture, or at least partly fused to metaventrite, suture incomplete or absent. Metacoxal plates well developed, more or less uniform, or weakly developed; not concealing most of basal abdominal ventrite. Metacoxae not greatly enlarged; horizontally oriented, or obliquely oriented. Lateral arms of metendosternite short or absent, or moderately to very long. Metendosternal laminae absent. Ventrolateral processes of metendosternite absent or weakly developed. Anterior process of metendosternite moderately long, or short or absent. Anterior tendons of metendosternite moderately or very close together, or on lateral arms or not apparent. Apical portion of metendosternite not or only slightly emarginate.

Hind wing. Hind wing well developed, or highly reduced or absent; with normal transverse folds. Radial cell of hind wing highly reduced or absent; incomplete or absent. Ratio of length of apical area to total wing length less than 0.2, or 0.20–0.35, or 0.36–0.5. Apical area of hind wing without veins or sclerotizations. Medial bar of hind wing not crossed by fold. Free veins in medial area of hind wing 5 or 6, or 4, or 3 or fewer. Oblongum cell of hind wing absent. Medial fleck of hind wing absent; absent or not partly bisected by a vein. Wedge cell of hind wing absent. Anal lobe of hind wing present. Posterior edge of hind wing without fringe of long hairs.

Legs. Femoral attachment of mid trochanter transverse or slightly oblique, or strongly oblique with base of femur separate from coxa. Mesotrochanter not reduced or concealed from below. Metafemur not much wider than mesofemur. Mesotibia not strongly widened. Outer edge of mesotibia simple, crenulate or denticulate, or with distinct teeth or long spines. Outer subapical edge of mesotibia without antenna cleaner. Preapical surfaces of mesotibia without ridges or combs. Outer apical angle of mesotibia simple or slightly produced, without lobe, teeth or spines, or with rounded lobe or process, sometimes bearing spines. Inner apical angle of mesotibia not or slightly produced, without tooth. Mesotibial spurs glabrous or absent; absent. Mesotarsus with 5 distinct tarsomeres (pentamerous). Tarsomeres on hind leg at least as many as on mid leg. Tarsomeres on fore leg at least as many as on mid leg. Mesotarsomere 1 well developed and visible. Preapical mesotarsomeres together longer than apical one. Penultimate mesotarsomere not distinctly shorter than antepenultimate. Ventral mesotarsal lobes absent, or on penultimate tarsomere only, or on more than one tarsomere. Mesotarsal claws paired; subequal in length and similar in form and angle of inclination; simple. Appendage on each tarsal claw absent. Mesotarsal claws without setae near base. Mesotarsal empodium present and exposed, or absent or concealed; absent or with 2 or fewer setae. Outer edge of protibia simple and rounded to carinate but without lobes or teeth, except at apex. Outer apical angle of protibia simple or slightly produced, without lobe, teeth or spines. Inner subapical edge of protibia without antenna cleaner. Protibial spurs absent. Hind legs without swimming hairs. Preapical surfaces of metatibia without ridges or combs. Metatibial articular area not to only moderately expanded, narrowly oval or oblique. Metatibial spurs absent.

Abdomen. Number of abdominal ventrites 2, or 5. Number of basal ventrites connate none, or five or six. Abdominal sternite 2 apparently absent. First ventrite not completely divided by metacoxae. Suture between ventrites 1 and 2 distinct. Suture between ventrites 2 and 3 distinct. Ventrite 4 articulated with or connate with both 3 and 5. Postcoxal lines on ventrite 1 absent, or 1 pair, strongly curved or recurved, or 1 pair, straight or slightly curved. Ventrite 1 not much longer than 2, or much longer than 2. Abdominal process acute or narrowly rounded, or absent. Ventrite 5 in female without circular depression. Posterior edge of ventrite 5 not crenulate, or crenulate. Last visible tergite and-or sternite (7 or 8) not forming terminal spine. Tergite and sternite 7 separated by membrane or distinct suture. Subapical abdominal luminous organ absent. Ventrites without setose patches or foveae. Functional spiracles on abdominal segment 8 present, or absent. Functional spiracles on abdominal segment 7 present. Functional spiracles on abdominal segment 6 present. Functional spiracles on abdominal segment 5 present. 7th abdominal spiracles located in pleural membrane. 6th abdominal spiracles located in pleural membrane. 5th abdominal spiracles located in pleural membrane. Anterior edge of sternite 8 in male without median strut, or with median strut. Pygidium (sclerotized tergite 7 or 8) more or less horizontal. Anterior edge of sternite 9 in male without median strut. Tergite 9 in male truncate, or deeply emarginate, or almost completely divided into two parts, or completely fused to tergite 10. Tergite 10 in male well developed and free, or partly fused to tergite 9, or completely membranous or fused to tergite 9.

Aedeagus trilobate; symmetrical. Anterior edge of tegmen or phallobase without struts. Parameres individually articulated to phallobase or base of penis, or fused to phallobase or base of penis but free from one another, or partly or entirely fused together but articulated to phallobase; not outwardly hooked. Penis without dorsal and ventral lobes. Anterior edge of penis with paired struts.

Illustrations. • Aulonothroscus. Aulonothroscus sp. Locality: Australia. Artist: S. P. Kim. Copyright CSIRO. Reference: Lawrence and Britton 1991. • Neocrowsonia. Neocrowsonia viatorica Kistner & Abdel-Galil. Locality: Southern Africa. Photo: J. Green. Copyright CSIRO. • Pactopus. Pactopus horni LeConte. Locality: Western North America. Photo: K. Smith. Copyright CSIRO. • Potergus. Potergus sp. Locality: New Guinea. Photo: K. Smith. Copyright CSIRO.


The interactive key provides access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting specified attributes, and summaries of attributes within groups of taxa.

Cite this publication as: ‘Lawrence, J.F., Hastings, A.M., Dallwitz, M.J., Paine, T.A., and Zurcher, E.J. 2000 onwards. Elateriformia (Coleoptera): descriptions, illustrations, identification, and information retrieval for families and subfamilies. Version: 9th October 2005. http://delta-intkey.com’.

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