The Prosoeca peringueyi (Diptera: Nemestrinidae) Pollination Guild in Southern Africa: Long-Tongued Flies and Their Tubular Flowers

Abstract

A guild <>( 28 winter-and s[)ring-flowering specit-s of two planl faniilics, IriJaceac and Gcraniact^ae.with intense purple to crimson (lowers ajid exlreniely long and slender perianth tubes, is pollinated exclusively hy two long-t<)ngnrd hies of the family Nemestrinidae.The two species of flies, Prosorra peringuryi and P. sp. nor., are active in the late winter and sj)ring, have large Ixxhes, moulhparts 2()-S() mm long, and forage for nectar while hovering.Plant.spollinated l)v these two flies share a suite of converginil floral characteristics, including a straight or sliglitly curved fl(>ral tube at least 20 nun and u[) l() 70 nun long, relatively short petals or tc[)als colored [jredomlnantly dark Mac-or nH|-j)urplc uith pale iH'ctar guides, and anthers and stigmas exscrted from the lube and usually unilateral in orientation.With one exce[)tion, the Dowers of all species secrete large amounts of nectar of relatively constant total sugar concentration, mostly 24-29%, and high sucrose: hexose ratio.M(>st r»iembers of the guild have odorless flowers.The long floral tube makes nectar unavailable to most insects, including a variety (A bees.wasp>, and otln-r flics that pollinate plant-which co-occur with members of the long-tubed flower guiltl.The two Prosocca sp<M'ies have mouthparts long enough to forage effectively on these long-tubed flowers, and they are also effective pollinators because pollen adheres to llieir Inxlies and is transjiorted from flower to flower.The (lies visit a wide range of f)lants but are effective pollinators ordy of those with tube lengths greater that their proboscis lengths.We have identified four imitually exclusive sit<'s of [)otlcn deposition ym the insects' bodies: when two or more members of the guild co-occur, each species ty|)icall\ utilizes a different pollen de[>osilion site.This suggests that jjollen contamination is detrimental to reproductive succ<^ss.Differ-<'nlial jiollen (h^position sites may have evolved in res|>onse to seh^^tion for reduced pollen contamination.Since 27 of the 28 plant species appear to depend ex<lusively on these two s[)ecies of Prosoeca for pollination, these flics must l)c considered kevstone species in the ecos\ stems where the\ occur.' This research was supported by National Geographic Societv (irant 48U>-92.W<* gralefulK acknowledge the work of h.-F.van Wyk.Hand Afrikaans LUiiversity.