Champion Pollinators

CHAMPION POLLINATORS by Peter Goldblatt, Missouri Botanical Garden, St. Louis, Missouri and John C. Manning, Compton Herbarium, National Botanical Institute, Kirstenbosch outhern Africa abounds in coast species Moegistorhynchus Philoliche gulosa and P rostrata, plants that have flowers with longirostris which has a tongue as and several nemestrinids, Slong, slender floral tubes and long as 70 to 80 mm. Several other including six species of the genus in an unusual range of animals flies have tongues up to 40 mm, Prosoeca, one of Stenobasipteron, with long mouthparts that feed on still amazing when one considers and at least two species of the the sugar-rich nectar in genus Moegistorhynchus. the base of the tubes. The These flies with super- animals that feed on the long mouthparts occur nectar, all potential polli- throughout southern nators of these plants, Africa, their collective include sunbirds with range extending from long bills and tongues and southern Namibia to the a variety of different Cape Peninsula in the groups of insects with west, along the elongated mouthparts. mountains of the Among these insects are southern Cape and butterflies and moths, through Lesotho and flies, including bee flies KwaZulu-Natal into (Bombyliidae) and Mpumalanga, Northern acrocerid flies Province and Swaziland. (Acroceridae), and some None of these flies is bees. These flies and bees known from tropical have mouth parts up to Africa, which also seems 8-12 mm long and visit to lack plants associated flowers with floral tubes with long-proboscid fly of moderate length, pollination. usually in the 10-15 mm Our interest in long- range. Such pollinators proboscid fly pollination are not uncommon and began with an investi- they occur all over the gation of the taxonomy, world. biology and evolution of Southern Africa is also the genus Lapeirousia, home to a special group of and subsequently that of long-proboscid polli- the genus Gladiolus, nators: flies with mouth- both members of the parts mostly exceeding Active in the spring in the Western Cape and Namaqualand, plant family Iridaceae. 20 mm, one of only a few Prosoeca peringueyi is the sole pollinator of a range of wild These genera exhibit kinds of organisms flowers with long floral tubes and bright red to purple petals, such major radiation and as Lapeirousia silenoides. Photo: J. Manning. capable of taking nectar speciation in southern from plants with super- Africa, and in both there long, narrow floral tubes that that the fly has no way to retract its has been significant adaptive exceed 20 mm in length. Such flies prodigious appendage, but must fly radiation for a variety of polli- are remarkable among pollinators with it extended forward or tucked nation systems. Many species of for their needle-like mouthparts loosely below its body. Flies with both genera have flowers with are longer than their bodies, these super-long mouthparts particularly long tubes and secrete sometimes up to three times as include some twelve known relatively large amounts of nectar long. Many of the plants that they species in two fly families, the that is rich in sucrose. Our work visit to forage for nectar have Nemestrinidae (tangle-veined flies on Lapeirousia gave us the first slender floral tubes exceeding - a fairly uncommon animal) and indications of the presence of 30 mm in length and sometimes the Tabanidae (horseflies - short- guilds (see accompanying box) of up to 70 mm. Clearly, these long- proboscid species which bother plant species using particular long- proboscid flies and the plants cattle and humans alike as the proboscid fly species to achieve with which they are associated females painfully bite the skin to their pollination. have co-evolved and form a close obtain the blood meal they require In Namaqualand, in the interior ecological mutualism. to complete their life cycle). west coast of South Africa, we Champion among long- The cast of long-proboscid flies discovered that the carmine-red proboscid flies is the Cape west includes the two horseflies, flowers of Lapeirousia silenoides (Springbok painted petals) were named. And on the Hantamsberg probable pollinator of another pollinated exclusively by one near Calvinia, in the western Lapeirousia, 1. anceps (by the species of fly, Prosoeca peringueyi. Karoo, Babiana flabellifolia and - entomologist, A. J. Hesse, and At particular times of the day and Romulea hantamensis, which also reported by the German biologist, in sunny, warm weather this large have long-tubed, purple flowers, Stefan Vogel in 1954). We later fly, which has mouthparts 30 to 40 were visited exclusively by this found this fly pollinating not only mm long, could be found foraging species of Prosoeca. The puzzle as 1. anceps, but several plants with for nectar on the flowers of to why long-tubed purple or similarly shaped and coloured 1. silenoides. Its violet-coloured magenta flowers are so common flowers with long floral tubes. Near pollen deposited all over the face only north of the Olifant's River Yzerfontein on the Cape west coast of the flies can often be seen with valley was explained. They are M. longirostris also pollinates the naked eye. We soon noticed adapted for pollination by these Pelargonium stipulaceum, and that Properingueyi also visited two flies which are found only other species of Iridaceae with similarly coloured and shaped north of Clanwilliam. cream flowers, including Babiana flowers of other plants tubulosa, Geissorhiza that grew nearby. Often exscapa, Gladiolus the flies would visit the angustus and Ixia panic- brilliant magenta flowers ulata. The cream- of Pelargonium incras- flowered orchid, Disa satum, a species of the draconis is also part of Geraniaceae fairly this guild. In the common in Namaqualand. Olifant's River valley Flies would also visit the near Clanwilliam we flowers of Babiana again found this fly, this species (Iridaceae) with time pollinating both long-tubed, dark blue- 1. anceps and 1. fabricii, violet flowers and as well as Geissorhiza Hesperantha latifolia with exscapa and Tritonia deep red flowers. It crispa. gradually dawned on us A second fly, the that a wide range of tabanid Philoliche spring-blooming, intense gulosa, shares this same red, purple or bluish series of plants, but flowers with pale mainly outside the range coloured markings, of M. longirostris. complete absence of scent, Ph. gulosa has slightly and a long floral tube shorter mouthparts than containing sugary nectar M. longirostris and were visited solely, but presumably is at a slight indiscriminately by disadvantage in Prosoeca peringueyi. competing with This pattern was also M. longirostris for nectar. evident to the south in the Their ranges overlap Olifant's River and only to a small extent, Bidouw valleys where With the longest proboscis of any fly, Moegistorhynchus however, and both Prosoeca peringueyi longirostris is the only insect able to reach into the base of the species are able to utilize could be found visiting floral tubes of plants like Lapeirousia anceps to feed on the ample the same set of plants. It the flowers of Lapeirousia nectar located there. Moegistorhynchus appears to be attracted particularly to cream and pink flowers with darker markings. is notable that the length jacquinii, 1. violacea or Photo: J. Manning. of the floral tube usually 1. pyramidalis, different tracks very closely the species of Babiana, Sparaxis A second group of Namaqualand length of the visiting insect's variegata (Iridaceae), and and Cape west coast plant species mouthparts. The floral tube in the Pelargonium magenteum, all formed another guild with flowers plant species is much longer in having violet to dark reddish adapted for pollination by different populations visited by M. longi- flowers with pale markings and a species of long-proboscid flies. rostris than in those visited only by long, nectariferous floral tube in They also have long-tubed flowers Ph. gulosa, graphically illustrating common. On the Bokkeveld with ample amounts of sweet this phenomenon. Plateau near Nieuwoudtville in the nectar, but the flowers are white to In the mountains of the Western Northern Cape Province we found pale pink and have red to purple Cape, including the Cape a local variation of what was markings that seem to function as a Peninsula, we have seen some of becoming a familiar pattern. visual signal. We first saw the. the same plant species that we Purple-flowered and long-tubed nemestrinid fly, Moegistorhynchus found being visited by Moegistor- Lapeirousia oreogena, 1. jacquinii, longirostris on a species of hynchus longirostris and/or Babiana framesii and B. sambucina Lapeirousia, 1. fabricii in Philoliche gulosa, as well as others were being visited by a second Namaqualand. This fly had already with a very similar appearance, species of Prosoeca as yet not been recorded as a visitor and being visited by other flies including P. rostrata and Prosoeca nitidula. These plants evidently belong to a greater Moegistorhynchus Philoliche pollination guild in the southern African winter-rainfall zone that involves cream to pink- flowered plant species that flower in the spring and early summer, September to November or December. All these long-proboscid flies have'a random foraging behaviour. They will visit flowers of the different members of their respective guilds quite indiscriminately, and thus carry pollen of several species on their bodies, a feature easy to determine with the naked eye by the heavy deposits of differ- ently coloured pollen, and by microscopic analysis of pollen removed from their bodies. The problem of pollen clogging (see accompanying box) however, does not occur. This is because at sites where plant species use a particular fly for pollination each species has anthers so positioned that pollen is consistently deposited on a different part of the fly's body. For example, at sites in Namaqualand, pollen of Lapeirousia silenoides is deposited on the frons (front part of the head) of Prosoeca peringueyi, that of Pelargonium on the lower thorax and of Babiana dregei or B.

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