Cucujus Fabricius Platisus Erichson Palaestes Perty

Family Cucujidae Latreille 1802 (Coleoptera: Cucujoidea)

by
Michael C. Thomas
Florida State Collection of Arthropods



Pediacus

Contents




Introduction

    This is a small family of only four genera and 36 described species of mostly medium-sized, brightly colored, dorsoventrally compressed beetles found primarily under the bark of dead trees. (A fifth genus, Phloeostichus Redtenbacher, is discussed and illustrated, but its affinities remain controversial and it is currently placed in the Phloeostichidae.) The literature on the family (in its narrow sense) is composed almost entirely of scattered descriptions and the family as a whole has never been revised, nor have any of the genera. Consequently, except for some regional works, there are no keys to species or any information on phylogenetic relationships within the family or between it and other families in the Cucujoidea. I anticipate revising this family on a worldwide basis in the future, but as that will require a considerable amount of time borrowing specimens, recording data, etc., I have prepared this webpage as a place to organize my thoughts and at the same time to provide some information on these interesting beetles. It should be considered a work in progress and the information presented here should be approached in that light.



Family Description

Adults: Small to moderate in size, 6mm - 25mm; elongate, parallel-sided, strongly dorsoventrally flattened; often brightly colored, red or yellow and black; pubescence inconspicuous to moderately pubescent.
    Head large, transverse, often distinctly triangular with well-developed temples (not Pediacus, although some species have a denticle behind the eye); nearly impunctate to densely punctate; antennae with 11 antennomeres, filiform to nearly moniliform, with or without a distinct club, antennomere III longest; antennae inserted laterally, insertion hidden; labrum very small, transverse, fused to clypeus; mandibles large, robust, with two apical and one subapical teeth (mandibles highly modified in males of Palaestes), mola not ridged; maxillary palpi with four palpomeres, terminal palpomere truncate apically; mentum transverse; ligula strongly V-shaped and membranous (except Platisus, where it is heavily sclerotized); labial palpi with three palpomeres, terminal palpomere truncate apically; eyes moderate, round, somewhat flattened to very convex.
    Pronotum quadrate to very transverse, usually smaller than head, without anterior angles except in Palaestes, laterally margined, dentate or denticulate, nearly impunctate to densely punctate, disc usually with depressions; prosternum broad, prosternal process moderate to relatively narrow; procoxal cavities narrowly separated, open posteriorly, with an anterolateral extension exposing trochantins; mesocoxal cavities open laterally; metasternum elongate; trochantins visible on pro- and mesocoxae; anterior coxae globose, middle coxae globose, hind coxae transverse; trochanters normal; femora pedunculate; tibiae slender, apical spurs small, subequal; tarsal formula 5-5-5 females, 5-5-4 males; protarsi on males with tarsomeres somewhat expanded laterally compared to those of female; claws simple; scutellum quadrate to pentagonal; elytra confusedly punctate, not striate (vague longitudinal lines visible in some species do not appear to be surface structures); scutellary striole absent; epipleural fold complete; metendosternite of normal hylecetoid type; wing venation varies within family, but generally well-developed, with radial cell complete (not Pediacus), radial recurrent present (not Pediacus), medial radial vein complete or nearly so; six veins behind M4 Cu, anal lobe present or absent.
    Abdomen with five visible sterna, sutures entire; intercoxal process acute; surface nearly impunctate to densely punctate. Male genitalia of two types: one inverted, with parameres ventrad of the median lobe and with a flagellum (Cucujus and Pediacus), and one in which the aedeagus lays on its side in the abdomen and lacks a flagellum (Platisus and Palaestes). Female genitalia with proctiger membranous, paraprocts and valvifers reduced to bacula, coxite two-segmented, and stylus apical.

Larvae: Known larvae (Palaestes larvae are unknown) dorsoventrally compressed, orthosomatic, well-sclerotized; vestiture consists of a few simple setae; color yellow to red-brown. Head protracted and prognathous, transverse, flattened and as wide or wider than prothorax; frontal arms lyriform; antennae long, with three antennomeres, antennomere II with sensorium; six pairs of stemmata; frontal suture absent; labrum free; mandibles broad, sclerotized, with three apical teeth, an acute prostheca, and a mola; ventral mouthparts retracted, maxillary articulating area well-developed, mala falciform; maxillary palpi with three palpomeres; labial palpi with two palpomeres. Legs long, five-segmented, and widely separated; abdomen with 10 segments, eighth normal to elongate; tergum IX bearing paired urogomphi supported on a short (Cucujus) to long (Pediacus) or very long (Platisus) median stalk; sternum IX and tenth segment reduced and concealed beneath tergum IX.



Phloeostichus

Phloeostichus Redtenbacher (Phloeostichidae: Phloeostichinae)

    Adults of Phloeostichus denticollis Redtenbacher (the only known species) are similar to adult cucujids in possession of the following character states: head abruptly constricted behind eyes; frontoclypeal suture absent; antennomere III longer than II and IV, and VII noticeably larger than VIII (as in Pediacus); tarsal formula 5-5-4 in males; the structure of the tarsi is identical to that found in Cucujus and Pediacus; lateral margins of pronotum unevenly denticulate; pronotum with dorsal impressions; front coxal cavity with lateral extension exposing trochantin; aedeagus inverted with articulated parameres. The hindwing venation is not inconsistent with the intergeneric variation found in Cucujidae (sens. str.).
    Some of these similarities may very well prove to be plesiotypic (e.g., exposed trochantin) or convergences (e.g., inverted aedeagus, and elongate antennomere III (which is present in some laemophloeids and silvanids, but not all)). The most conspicuous difference between Phloeostichus and Cucujidae (sens. str.) is the possession of longitudinally striate-punctate elytra in the former; all of the genera included in Cucujidae (sens. str.) have confusedly punctate elytra with no trace of striae. Phloeostichus adults are pubescent dorsally, but some species of Pediacus also are noticeably pubescent.
    There is an old description of the putative larva of Phloeostichus (Ganglbauer 1899) but it is not detailed enough to be useful. If Phloeostichus is not a cucujid, it is certainly closely related and may be valuable as an outgroup for phylogenetic analysis. An adequate description of its larva is badly needed.



Distribution

    The family is represented on all continents except Africa, but is richest in the Holarctic Region. Cucujus is Holarctic in distribution, with one species, represented by two subspecies, currently recognized from North America. The largest genus, Pediacus, is also Holarctic, but in the New World extends its distribution south into the Neotropics in Central America at high altitudes. It is the only other genus represented in North America, where seven species occur. Palaestes is confined to the Neotropics, also apparently at fairly high altitudes. Platisus is confined to the eastern half of Australia. Phloeostichus, whose affinities are controversial, is found only in central Europe.



Biology

    Despite the size and attention-grabbing coloration of these beetles, virtually nothing is known about their biology. They have usually been presumed to be predaceous and Smith and Sears (1982) reached that conclusion after a detailed study of the larval mouthparts of Cucujus clavipes in Canada. Adults and larvae both are usually found beneath the bark of dead trees. Larvae are known (if not adequately described) for all genera except Palaestes.




Table. Valid Genera and Species of Cucujidae
  Cucujus Fabricius Palaestes Perty Pediacus Shuckard Platisus Erichson
1 bicolor Smith abruptus Sharp andrewsi Thomas coloniarius Ollff
2 chinensis Lee & Sato freyreissi Heyden ater Grouvelle integricollis Reitter
3 cinnaberinus Scopoli nicaraguae Sharp bhutanicus Sen Gupta moerosus Pascoe
4 c. clavipes Fabricius nigriceps Waterhouse confertus Sharp obscurus Erichson
5 c. puniceus Mannerheim nigridens Sharp depressus (Herbst) zelandicus Marris & Klimaszewski
6 coccinatus Lewis scutellaris Sharp dermestoides (Fabricius)  
7 grouvellei Reitter tenuicornis Waterhouse elongatus Sen Gupta  
8 haematodes Erichson variipes Sharp fuscus Erichson  
9 imperialis Lewis   gracilis Thomas  
10 kempi Grouvelle   hesperoglaber Thomas  
11 mniszechi Grouvelle   japonicus Reitter  
12 nigripennis Lee & Sato   kurosawai Sasaji  
13 opacus Lewis   major Sharp  
14     mexicanus Sharp  
15      montivagus Champion  
16     ommatodon Thomas  
17     rufipes Grouvelle  
18     similis Sharp  
19     smirnovi Nikitsky and Belov  
20     stephani Thomas  
21     subglaber LeConte  
22     tabellatus Wollaston  




Key to the Genera of Cucujidae
1. Tarsomere I and IV much shorter than II and III; aedeagus inverted 2
1'. Tarsomeres I-IV subequal in length; aedeagus resting on side 3
2(1). Temple large, produced laterally beyond eye; large, brightly colored beetles (Holarctic) Cucujus
2'. Temple absent or represented at most by a small denticle; small, dull colored beetles (Holarctic) Pediacus
3(1'). Temple acute; intercoxal process of prosternum not as wide as a coxa (less trochantin); mandibles of males grotesquely modified; brightly colored (Neotropical) Palaestes
3'. Temple obtuse or absent; intercoxal process of prosternum wider than coxa (less trochantin); mandibles of males not modified; generally dull colored (Australian) Platisus




Table. Detail of Dorsal Structure of Heads of Adult Cucujidae
Cucujus Fabricius Platisus Erichson Palaestes Perty




Table. Hindwing Venation of Cucujidae
"Basic Plan" Wing* Cucujus
Palaestes Pediacus
Phloeostichus Platisus
*The "Basic Plan" wing was derived by superimposing images of the wings of all four genera; the assumption being that the common ancestor would have had the most complete venation.



Table. Male Genitalia of Cucujidae
Cucujus Pediacus
Palaestes Phloeostichus




Table. Coxal Cavities of Cucujidae
Cucujus Palaestes Phloeostichus




Table. Hind Tarsi of Male Cucujidae
Cucujus Palaestes




Table. Metendosternites of Cucujidae
Cucujus Pediacus