Recognition: The small size, oblong silhouette, depressed dorsum, deflexed head, tightly fitted pronotum against the elytral bases, and capitate antennae distinguish throscids.

 Habitus: Body oblong to elongate, compact; length approximately 1-3 mm; color red brown to black; vestiture fine, suberect. Head hypognathous, narrower than prothorax, deeply inserted into prothorax when reposed. Eyes oval, vertically oriented, coarsely faceted, deeply emarginate, often nearly divided by frontal canthus. Antenna 11-segmented, loosely capitate; insertions distant, on frons between eyes, beneath carinate ridge, received into prosternal grooves. Labrum articulate, visible. Mandible stout. Maxilla with palpus 4-segmented, apical segment triangular; labium with mentum small, narrowed anteriorly, palpus 3-segmented. Prothorax compact; pronotum trapezoidal, fitting closely to mesothorax and bases of elytra; hind angles extended, lateral margins fine, obsolete anteriorly; prosternum briefly lobed anteriorly, extended and narrowed posterior as intercoxal process fitting into mesosternal cavity; pronotosternal suture grooved to accept antenna; hypomeron subtriangular, with deep antennal cavities posteriorly; procoxal cavities open posteriorly. Scutellum small, triangular. Mesothoracic wing short, apical field subequal in length to main portion; venation reduced, radial cell open, wedge cell absent; medial and anal field veins greatly reduced to absent. Mesosternum short, deeply excavated medially; mesocoxae widely separated. Elytra entire, rounded at apex; striae shallow, punctate; intervals flat, finely to moderately punctured; epipleura broad basally, narrow apically. Metasternum large, quadrate, with or without oblique tarsal grooves; metacoxae with broad ventral lamina, shallowly excavate posteriorly to receive femur. Legs retractile; trochanters short, triangular; femora fusiform; tibiae slender, spinose; tarsi 5-5-5, filiform or with segment 4 with ventral membranous lobe, claw simple. Abdomen with 5 ventrites, all connate. Aedeagus trilobed; penis acute at apex; parameres attenuate, densely setiferous laterally; basal piece longer than parameres, proportionately large, deeply emarginate posteromedially. Female gonocoxite lightly sclerotized, narrow, elongate; stylus clavate, apical; baculi long, slender.

 Larvae are lightly sclerotized, grublike. Head small, prognathous, reduced; antenna short, sensorium as long as segment 3; labrum fused to head capsule, forming an inarticulate plate; mandibles narrowly elongate, flattened, fused to head capsule; maxilla reduced to a 3-segmented palpus; labium elongate, palpus 2-segmented. Legs short, 5 segmented, tarsungulus present. Tergite 9 with pair of small urogomphi. Tergite 10 obsolescent. Spiracles biforous, on mesothorax and abdominal segments 1-8; closing apparatus present.

 Ecology: Little is known about throscids. Adults are usually captured in traps or netted in late afternoon flights, at light traps, in flowers, recovered from duff and litter samples, near mammal burrows, in rotted wood, grain storage facilities, and on various foliage. Adults may be generalist pollen and mold feeders. They share an ability to click and "jump" with the Elateridae and Eucnemidae, by rapidly articulating the prothorax and mesothorax against a substrate. Adults are reported to possess four fat-body mycetomes containing three types of bacterial symbionts. Larvae have been found in blocky red rotted portions of oak logs, in fungusy soil samples, and in grass tussocks. Larvae of the European Trixagus dermestoides (L.) were found in a variety of soils, always near tree stumps, and under the litter. They are liquid feeders on outer portions of ectotrophic mycorrhizal roots (Burakowski 1975).

 Status of the Classification: With the removal of Lissominae to Elateridae (Lawrence & Newton 1995), the throscids have become a more clearly defined group. However, the family is in need of general study at all levels, and the position of certain exotic genera remains problematic. The family is closely related to the Eucnemidae and Elateridae. In Central America, Horn (1890) provided the most recent review of most species. The most diverse genus in the region is Aulonothroscus, and this is in need of revisionary study. Yensen (1980) provided a new key to the New World species of Trixagus.

 Diversity and Distribution: There are 152 described species worldwide, with 3 described Aulonothroscus species in the Central American fauna. Two apparently undescribed Trixagus species are known from Costa Rica. Most throscids occur in lowland and mid elevational forested environments.

KEY TO THE COSTA RICAN GENERA

 1. Metasternum with a deep oblique tarsal sulcus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aulonothroscus

Metasternum evenly arched, without sulci. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Trixagus

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 CLASSIFICATION OF THE COSTA RICAN GENERA

Genus: Aulonothroscus Horn, 1890

 Known Species: A. fraternus Horn, A. gradatus Horn, A. schaumii (Bonvouloir)

 Key to species: Horn (1890)

Aulonothroscus fraternus Horn

 Provincial Records: Guanacaste

 General Distribution: Costa Rica, Guatemala, Mexico

 Aulonothroscus gradatus Horn

 Provincial Records: Guanacaste

 General Distribution: Costa Rica, Guatemala

Aulonothroscus schaumii (Bonvouloir)

 Provincial Records: Guanacaste

 General Distribution: Argentina, Brasil, Guatemala, Costa Rica

Genus: Trixagus Kugelann, 1794

 Throscus Latreille, 1796

 Known Species: 2 spp., undescribed

 Provincial Records: Guanacaste

 General Distribution: northwestern Costa Rica

 Key to species: Yensen (1980)

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BIBLIOGRAPHY

BECKER, E.C. 1991. Throscidae (Elateroidea) (= Trixagidae), pp. 418-419. In Stehr, F.W., Immature Insects.

Kendall/Hunt Publ. Co., Dubuque.

BONVOULOIR, H. de 1859. Essai monographique sur la famille des Throscides. Paris.

BURAKOWSKI, B. 1975. Development, distribution and habits of Trixagus dermestoides (L.), with notes on the Throscidae and

Lissomidae (Coleoptera, Elateroidea). Annal. Zool., 32: 375-405.

HORN, H. 1890. Fam. Throscidae. Biologia Centrali Americana, 3(1): 193-209.

LAWRENCE, J.F. 1981. Coleoptera, pp. 482-553. In Parker, S.P., Synopsis & Classification of Living Organisms.

McGraw-Hill Book Co., New York.

LAWRENCE, J.F. and A.F. NEWTON, JR. 1995. Families and subfamilies of Coleoptera (with selected genera, notes, references and

SCHENKLING, S. 1928. Fam. Throscidae. Coleopterorum Catalogus, 11(101): 1-26.

YENSEN, E. 1980. A new species of Trixagus from Panama and a key to New World Trixagus (Coleoptera: Throscidae).

Coleopts. Bull., 34: 257-261.

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