Overview.
Members of the Hybosoridae are distinguished from other scarabaeoids
by their prominent mandibles and labrum and by their 10-segmented
antenna with a 3-segmented club in which the basal segment is hollowed
out to receive the penultimate and ultimate segments (fig. ). Other
than adults being attracted to lights, little is known about the biology
of members of this subfamily. In the New World fourteen genera occur,
one of which was introduced.
Description. Length 5.0-7.0
mm. Shape oval, dorsal surface convex. Color light brown to black,
shining. Head not deflexed. Antennae 10-segmented with 3-segmented,
opposable club (last 2 segments tomentose), first segment of club
hollowed to receive segments 2 and 3 [fig. ]), basal segment of antenna
expanded apically. Eyes with eucone ommatidia, divided by reduced
canthus. Clypeus lacking tubercle or horn. Labrum truncate, produced
beyond apex of clypeus, prominent. Mandibles produced beyond apex
of labrum, prominent, external edge rounded, apex pointed. Maxillae
with 4-segmented palpi; labium with 4-segmented palpi. Pronotum convex,
base wider than elytral base. Elytra convex, surface polished, glabrous.
Pygidium concealed by elytra. Scutellum exposed, triangular. Legs
with anterior coxae conical, contiguous; mesocoxae contiguous; protibiae
tridentate on outer margin, apex with one spur; meso- and metatibia
with prominent, oblique ridge, apex with 2 spurs; spurs mesad, adjacent
(not separated by basal metatarsal segment); tarsi 5-5-5; claws equal
in size, simple; empodium short, not extending beyond fifth tarsal
segment, with 2 setae. Abdomen with 6 free sternites (first sternite
obscured by hind coxae except at lateral edges); 8 functional abdominal
spiracles, situated in pleural membrane (spiracles 1-7) and in tergite
(spiracle 8). Wings well developed, with 2 apical detached veins.
Male genitalia variable. References: Cooper 1983, Scholtz 1990.
Classification Status.
The Hybosoridae is considered as a family within the Scarabaeoidea
or as a subfamily of the family Scarabaeidae. In this volume, we follow
Gardner (1935), Paulian (1939), and Lawrence and Newton (1995) and
consider the group a family. Hybosorid larvae are distinct and are
the primary reason that the group is treated as a family. Larvae possess
prothoracic and mesothoracic stridulatory structures and three truncate
lobes at the apex of the labrum, both of which are unique to this
group. In adults, the form of the antenna (10-segmented with a 3-segmented
club, the first segment hollowed to receive segments two and three)
is unique. The Hybosoridae is hypothesized to be intermediate between
the Ochodaeidae and Ceratocanthidae (Scholtz et al. 1988) or
intermediate between the Trogidae and Ceratocanthidae (Howden and
Gill 1988). Aside from revisions of some genera and catalogs, little
systematics work has been conducted on this group.
Distribution. The Hybosoridae
contains 28 genera world-wide and about 180 species (Allsopp 1984;
Martinez 1994). Species are widely distributed in the tropics. Fourteen
genera and about 60 species occur in the New World. Phaeochrous
emarginatus Laporte, a species that occurs in Africa, Australia,
and India, was once reported from California, but the species is not
established in California and the record was probably in error (Evans,
pers. comm. 1998).
New
World Genera of Hybosoridae
Hybosoridae
Anaides Westwood 1841
Apolonychus Westwood 1846
Callosides Westwood 1846
Chaetodus Westwood 1846
Coilodes Westwood 1946
Cryptogenius Westwood
Diamothoracodes Petrovitz 1970
Dicraeodon Erichson 1847
Hapalonychoides Martinez
Hybochaetodus Arrow 1909
Hybosorus MacLeay 1819
Pachyplectrus LeConte 1874
Metachaetodus Borre 1886
Ecology. Little life history
information is known for hybosorids. Adults feed on carrion in the
early stages of decomposition and are attracted to lights at night.
Adults of Hybosorus are known to stridulate. Larvae stridulate
by rubbing the front legs against the anterior margin of the epipharynx,
a trait unique to the Hybosoridae (Paulian 1939). Larvae have been
collected in decomposing plant material.
Larvae. Form scarabaeoiform
(C-shaped, cylindrical). Color creamy-white or yellow (except at caudal
end which may be darkened by accumulated feces). Cranium heavily sclerotized,
brown to dark brown. Antennae 3 or 4-segmented (if 3-segmented, then
third and fourth segments fused). Frontoclypeal suture distinct. Labrum
at apex with 3 truncate lobes. Epipharynx with row of setae on each
chaetoparia, a blunt tooth in the haptomeral region, and united tormae.
Maxilla with galea and lacinia distinctly separate; maxillary stridulatory
area consisting of a row of conical teeth; maxillary palp 3- or 4-segmented.
Abdominal segments 1-6 with 3 annuli, each with 1 or more transverse
rows of short setae. Spiracles cribriform, with closing apparatus.
Venter of last abdominal segment with raster consisting of 2 curved
rows of many short setae that converge caudally. Legs 4-segmented,
well developed, with stridulatory apparatus on pro- and mesothoracic
legs, each with a well-developed claw. References: Ritcher 1966; Scholtz
1990.
References
Cited
ALLSOPP,
P. G. 1984. Checklist of the Hybosorinae (Coleoptera: Scarabaeidae).
Coleopterists Bulletin 38: 105-117.
COOPER,
J. B. 1983. A review of the Nearctic genera of the family Scarabaeidae
(exclusive of the subfamilies Scarabaeinae and Geotrupinae) (Coleoptera),
with an evaluation of computer generated keys. Doctoral Thesis, Department
of Biology, Carleton University, Ottawa, Ontario, Canada. 1,121 pp.
GARDNER,
J. C. M. 1935. Immature stages of Indian Coleoptera (16) (Scarabaeidea).
Indian Forest Rec. (New Series) Ent. 1:1-33.
HOWDEN,
H. F. and B. D. GILL. 1988. A fourth genus of unusually modified Ceratocanthinae
(Coleoptera: Scarabaeidae) from South Africa. Canadian Journal of
Zoology 66: 2077-2079.
LAWRENCE,
J. F. and A. F. NEWTON, JR. 1995. Families and subfamilies of Coleoptera
(with selected genera, notes, and references and data on family-group
names), pp. 779-1006. In J. Pakaluk and S. A. Slipinski (eds.),
Biology, Phylogeny, and Classification of Coleoptera. Papers Celebrating
the 80th Birthday of Roy A. Crowson. Muzeum i Instytut Zoologii
PAN, Warszawa, Poland.
MARTINEZ,
A. 1994. Notas sobre Hybosorinae (Coleoptera: Scarabaeidae), II. Elytron
8: 223-239.
PAULIAN,
R. 1939. Les caractères larvaires des Geotrupidae (Col.) et leur importance
pour la position systématique du groupe. Bulletin de la Société Zoologique
de France 64: 351-360.
RITCHER,
P. O. 1966. White Grubs and Their Allies: A Study of North American
Scarabaeioid Larvae. Oregon State University Press, Corvallis.
219 pp.
SCHOLTZ,
C. H. 1990. Phylogenetic trends in the Scarabaeoidea (Coleoptera).
Journal of Natural History 24: 1027-1066.
SCHOLTZ,
C. H., D. D'HOTMAN, A. V. EVANS, and A. NEL. 1988. Phylogeny and systematics
of the Ochodaeidae (Insecta: Coleoptera: Scarabaeidae). Journal of
the Entomological Society of South Africa 51: 207-240.
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