Overview of the lady beetle tribe Diomini (Coleoptera: Coccinellidae) and description of a new phytophagous, silk-spinning genus from Costa Rica that induces food bodies on leaves of Piper (Piperaceae)

Abstract

A new genus of lady beetle, Moiradiomus gen. nov. (Coleoptera: Coccinellidae Latreille, 1807: Diomini Gordon, 1999 ), and four new species are described from Costa Rica, representing the first known occurrences of obligate phytophagous lady beetle species outside of the tribe Epilachnini Mulsant, 1846 (sens. Ślipiński 2007). The new species are described, illustrated and keyed, and their life histories discussed. Each species of Moiradiomus occurs on a separate species of Piper L., 1753 (Piperaceae Giseke, 1792), where the larva constructs a small silken tent between leaf veins and inside this shelter induces the production of food bodies, which are its exclusive source of food. Background information is provided on lady beetle trophic relations and other insect/Piper symbioses. The taxonomic history of Diomus Mulsant, 1850 and related species in the tribe Diomini is reviewed and existing errors in observation, interpretation, identification, and classification are corrected in order to provide a more meaningful context for understanding the new genus. The tribe Diomini is rediagnosed and recircumscribed to include Diomus, Decadiomus Chapin, 1933, Heterodiomus Brèthes, 1925, Dichaina Weise, 1923, Andrzej Ślipiński, 2007, and Moiradiomus. Magnodiomus Gordon, 1999 and Erratodiomus Gordon, 1999 are removed from Diomini and transferred to Hyperaspidini Costa, 1849, subtribe Selvadiina Gordon, 1985 stat. nov. Mimoscymnus Gordon, 1994 and Planorbata Gordon, 1994, originally described in Coccidulini Mulsant, 1846 are also transfered to Hyperaspidini and placed in Mimoscymnina subtribe nov. (type genus Mimoscymnus). The main morphological characters distinguishing Diomini and Hyperaspidini are described and illustrated. A key to genera of Diomini sensu novo is provided. The identification of the Australian Diomus species illustrated in Gordon’s publication on North American lady beetles is corrected from D. pumilio Weise, 1885 to D. tenebricosus (Boheman, 1859), however specimens recently collected in California do not match these genitalic illustrations and are identified as true D. pumilio. The following species of Diomus are transferred to Decadiomus as new combinations: D. balteatus (LeConte, 1878), D. floridanus (Mulsant, 1850), D. amabilis (LeConte, 1852), D. liebecki (Horn, 1895), D. myrmidon (Mulsant, 1850), D. humilis (Gordon, 1976), D. pseudotaedatus (Gordon, 1976), D. taedatus (Fall, 1901), D. bigemmeus (Horn, 1895), and D. austrinus (Gordon, 1976). Decadiomus seini Segarra, 2014 is placed as a junior synonym of D. austrinus. The following new species of Moiradiomus are described: M. clotho sp. nov., M. lachesis sp. nov., M. atopos sp. nov., M. nanita sp. nov.