Synonyms
Scymnus (Diomus) Mulsant, 1850: 951. TS: Coccinella thoracica Fabricius, 1801.
Amidellus Weise 1923. TS: Scymnus ementitor Blackburn, 1895.
Diagnosis
Diomus includes small setose coccinellid species that have abdominal postcoxal lines meeting posterior margin of first abdominal ventrite combined with simple pronotum, 11-segmented antenna with 3-segmented club and 3-segmented tarsi.
Description
Length 1.2-3.5 mm. Body elongate-oval and weakly convex; winged; dorsum uniformly hairy; head dorsally not covered by pronotum. Elytral colour variable. Head transverse; eyes finely facetted, weakly emarginate and moderately separate on vertex. Antenna 11-segmented; slightly shorter than head capsule with pedicel narrower than scape; antennomere 3 elongate; antennal club compact, 3-segmented. Terminal maxillary palpomere distinctly expanded apically. Pronotal disc evenly convex. Prosternum moderately long in front of coxae, arcuate; prosternal process broad usually with complete carinae. Anterior margin of mesoventrite straight medially. Mesoventrite slightly narrower than coxal diameter; Metaventral postcoxal lines strongly recurved. Elytral epipleuron very narrow, incomplete apically, not foveate. Tibial spurs absent. Abdominal postcoxal line merging with hind margin of ventrite. Male terminalia. Parameres and phallobase symmetrical; penis guide symmetrical, or asymmetrical. Parameres articulated with phallobase. Penis stout, consisting of single sclerite; basal capsule weak to absent. Apodeme of male sternum 9 very narrow and rod-like. Female terminalia. Coxities broad plates; styli absent; infundibulum absent; sperm duct simple, uniform in diameter. Spermatheca worm-like, without clear ramus or nodulus; spermathecal accessory gland adjacent to sperm duct.
Distribution and Biology
Probably one of the largest genera in Coccinellidae with worldwide distribution. Diomus species occur all over Australia but there is a significant increase of species diversity in the subtropical and tropical regions and adjacent islands. There is approximately 80 described and undescribed species in Australia. Very little is known about biology of the genus. Host lists include mostly aphids, mealy bugs, scale insects and whiteflies. The most common Australian species, D. notescens (Blackburn) has been reared from Eriococcus on Eucalyptus and Acacia.
Genus References
Gordon, R D. 1976. The Scymnini (Coleoptera: Coccinellidae) of the United States and Canada: Key to genera and revision of Scymnus, Nephus and Diomus. Bulletin of the Buffalo Society of Natural Sciences, 28: 1-362.
Mulsant, M E. 1850. Species des Coléoptères Trimcres Sécuripalpes. Annales des Sciencies Physiques et Naturelles, d'Agriculture et d'Industrie, publiées par la Société nationale d'Agriculture, etc., de Lyon, Deuxicme Série, 2: xv + 1-1104 (part 1 pp. 1-450; part 2 pp. 451-1104).
Iablokoff-Khnzorian, S. M. 1976. Die paläarktischen Genera der Marienkäfer - Tribus Scymnini nebst Bemerkungen über Scymnus fuscatus (Coleoptera, Coccinellidae). Etomologia Germanica, 2, (4): 374-80.
Sasaji, H. 1971. Coccinellidae (Insecta: Coleoptera). Fauna Japonica. Academic Press of Japan, Tokyo. 16 pls., 345 pp.
Slipinski, A. 2007. Australian Ladybird Beetles (Coleoptera: Coccinellidae) their biology and classification. ABRS, Canberra. 286 pp.
Weise, J. 1923. Results of Dr. E. Mjöberg's Swedish Scientific Expedition to Australia 1910-1913. 31. Chrysomeliden und Coccinelliden aus Queensland. Arkiv för Zoologi, 15(12): 1-150.
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