Colocasiomyia (Diptera: Drosophilidae) revised phylogenetically, with a new species group having peculiar lifecycles on monsteroid (Araceae) host plants

Abstract The phylogeny of Colocasiomyia ( D rosophilidae) is analysed using data for 70 morphological characters, many of which are re‐evaluated from or added to those used previously, for an expanded taxon sample of 24 Colocasiomyia ingroup species. A special focus is put on three species, of which two have remained unresolved for their relationships to other Colocasiomyia species, and the other is a newly discovered species. The analysis results in a single, most parsimonious cladogram, in which a clade comprising the three focal species is recognized along with other clades recovered for the known species groups of Colocasiomyia . Based on this, a new species group—the gigantea group—is established, including Colocasiomyia gigantea ( O kada), C . rhaphidophorae G ao & T oda, n.sp. and C . scindapsae F artyal & T oda, n.sp. These species of the gigantea group breed on inflorescences/infructescences of the subfamily M onsteroideae ( A raceae) exceptionally among Colocasiomyia species, most of which use plants of the subfamily A roideae as their hosts. Colocasiomyia gigantea uses Epipremnum pinnatum ( L .) E ngler, C . rhaphidophorae uses Rhaphidophora hookeri S chott and C . scindapsae uses Scindapsus coriaceus E ngler as their hosts. The host plants of the gigantea group are epiphytes and differ in the structure of spadix and the fruiting process from those of the A roideae. To understand how the species of the gigantea group adapt to properties of their host plants, their reproductive ecology—most intensively that of C . gigantea —is investigated. The lifecycle of C . gigantea is characterized by its relatively slow embryonic development (taking approximately 6 days), the very long duration of the full‐grown first instar within the egg capsule (approximately three months) until dehiscence of host infructescence, and its relatively fast larval and pupal development (taking approximately 11 or 12 days). Some morphological adaptations and the reproductive strategy in terms of ‘egg size vs. number’ trade‐off are discussed in relation to their reproductive habits and peculiar lifecycles.