The South African keystone pollinator Moegistorhynchus longirostris (Wiedemann, 1819) (Diptera: Nemestrinidae): notes on biology, biogeography and proboscis length variation

Moegistorhynchus longirostris Wiedemann, 1819 has the longest proboscis relative to body size of all known insects. It is a keystone species along the west coast of South Africa, where it pollinates, partly or exclusively, the long-tubed flowers of at least 20 species of Iridaceae, Geraniaceae and Orchidaceae. M. longirostris has been widely discussed in the pollination biology literature and has a suggested co-evolutionary arms race between it and the long-tubed flowers it pollinates. A current taxonomic revision has presented new biogeographical and morphometric data. Available records suggest that the species is widely distributed along the west coast of South Africa between about 29 degrees 30'S and 34 degrees 15'S, a distance of almost 500 km. It is restricted to sandy, lowland coastal plains at less than 300 m, where it occurs in nine different vegetation types across seven bioregions and is consequently not a habitat specialist. Proboscis length from 13 localities ranged from 32 to 83 mm, and mean proboscis length at these localities from 32 to 71 mm. There was a decline in proboscis length with increasing latitude south. Research investigating a possible allometric relationship between body size and proboscis length, and between latitude and proboscis length, is required.