Hidden Diversity-A New Speciose Gall Midge Genus (Diptera: Cecidomyiidae) Associated with Succulent Aizoaceae in South Africa.

Netta Dorchin,Stephany Van Munster,Cornelia Klak,Jonathan F Colville,Rauri C K Bowie

doi:10.3390/insects13010075

Abstract

Simple SummarySucculent Aizoaceae (often called “mesembs” or ice plants) form a dominant component of the Succulent Karoo in southern Africa, constituting one of the most species-rich families within the Greater Cape Floristic Region (GCFR). Despite the diversity and abundance of these plants, the diversity of insects specialized on them has never been surveyed methodically prior to this study. In a three-year study of the galling insects associated with succulent Aizoaceae in South Africa, we found that they support a rich community of gall midges (Diptera: Cecidomyiidae), virtually all of which are new to science. This is not surprising, given that knowledge of the Afrotropical fauna of gall midges is scarce, with most species described in the 1900s. Here, we describe the new genus Ruschiola with ten species from succulent Aizoaceae in Namaqualand, the Knersvlakte and the Cedarberg regions of South Africa based on morphological, molecular and life history data. The genetic data were particularly important in this study for differentiating taxa, given that Ruschiola species are very similar morphologically. Members of this genus develop in leaf galls or in plant tissues without visible gall formation, and are highly host specific.Aizoaceae (Caryophyllales) constitute one of the major floral components of the unique Greater Cape Floristic Region (GCFR), with more than 1700 species and 70% endemism. Within succulent Aizoaceae, the subfamily Ruschioideae is the most speciose and rapidly diversifying clade, offering potential niches for the diversification of specialized herbivorous insects. Nevertheless, insect diversity on these plants has not been studied to date, and knowledge of gall-inducing insects in the Afrotropics is generally scarce. Our recent observations indicate that succulent Aizoaceae in the GCFR support a rich and largely unstudied community of gall midges (Diptera: Cecidomyiidae). Here, we provide a first report of their diversity with a description of a new genus, Ruschiola Dorchin, and ten new species, based on morphological and molecular analyses of material collected during a three-year targeted survey across major GCFR vegetation types. A high degree of morphological uniformity in Ruschiola suggests recent diversification and necessitated the use of molecular data and laboratory rearing from host plants to verify species boundaries and host ranges.

Highlights

Aizoaceae is a large family of mostly leaf-succulent plants with over 1700 described species, the majority of which are confined to the winter rainfall region of southern Africa [1].The Aizoaceae constitute one of the most species-rich families within the Greater CapeFloristic Region (GCFR) and form a dominant component of the Succulent Karoo, an arid to semi-arid biome mostly found along the west coast of southern Africa that is notable for harboring the world’s richest flora of succulent plants [2]
Ruschiola attenuata from Mesembryanthemum splendens was retrieved as sister to all other species included here that develop in Ruschioideae host plants, paralleling the sister position of Mesembryanthemoideae relative to the Ruschioideae within Aizoaceae [5,27]
While it was obvious that these gall midges belong to the Lasiopterini, they were morphologically distinct from all other known genera in that tribe, justifying the description of a new genus

Summary

Introduction

Aizoaceae is a large family of mostly leaf-succulent plants with over 1700 described species, the majority of which are confined to the winter rainfall region of southern Africa [1].The Aizoaceae constitute one of the most species-rich families within the Greater CapeFloristic Region (GCFR) and form a dominant component of the Succulent Karoo, an arid to semi-arid biome mostly found along the west coast of southern Africa that is notable for harboring the world’s richest flora of succulent plants [2]. Aizoaceae is a large family of mostly leaf-succulent plants with over 1700 described species, the majority of which are confined to the winter rainfall region of southern Africa [1]. The Aizoaceae constitute one of the most species-rich families within the Greater Cape. Floristic Region (GCFR) and form a dominant component of the Succulent Karoo, an arid to semi-arid biome mostly found along the west coast of southern Africa that is notable for harboring the world’s richest flora of succulent plants [2]. 70% of Aizoaceae species are endemic to the Greater Cape Flora, i.e., the xeric Extra. The Ruschioideae exhibit a remarkably diverse array of growth forms and climatic and edaphic adaptations within their distribution [8], thereby offering a great number of potential niches for specialized herbivorous insects. The diversity of insects specialized on these succulent plants has never been surveyed methodically prior to the present study

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Results

Conclusion