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The Prosoeca peringueyi (Diptera: Nemestrinidae) pollination guild in southern Africa: long-tongued flies and their tubular flowers


Abstract | Materials and Methods | Results | Discussion | Literature

METHODS

Plant Species

Members of the guild were initially identified during the course of field research in 1992 and 1993 in connection with a study of pollination ecology of Lapeirousia subgenus Lapeirousia (Goldblatt et al., 1995). In this study species with purple to crimson flowers, white to cream nectar guides, and a perianth tube in excess of 30 mm were pollinated by Prosoeca peringueyi or P. sp. nov. or occasionally both. We then reviewed the literature for records of species with purple to crimson flowers recorded from the west coast of southern Africa. All species having a perianth tube at least 30 mm long or the anthers and stigmas held at least 30 mm from the base of the floral tube were listed for further study. These species were examined in the field whenever possible to obtain observations on nectar characteristics and pollinators Table 1. The apparent floral tube length was determined as the distance from base to the mouth of the tube. The actual floral tube length is less in some species due to the occlusion of the lower part of the tube and was determined empirically as the level down to which nectar could be freely extracted using a micropipette. Functional tube length was determined actual tube length plus the distance between the mouth of the tube and the mid point of the anthers. Measurements were made on a minimum of 10 individuals per population.

Complete distribution ranges of plant species were taken from the literature and supplemented by recent herbarium records. Voucher specimens were made for all populations studied. Plant vouchers are deposited at the Missouri Botanical Garden Herbarium, St. Louis (MO) and the Compton Herbarium, Cape Town (NBG).

Insect Species

Observations of insect foraging Figs. 1--6 involved 4-20 hours per species and included aspects such as the density and diversity of floral foragers and how they removed rewards from flowers. Insects observed probing the floral tube or brushing the anthers or stigmas were captured and killed in a jar using ethyl acetate fumes. Location of pollen deposits was based first on visual observation of foraging insects and later on examination of pinned specimens. Individual insects were washed of pollen after pinning by placing the insect on a glass slide and rinsing the whole body in 100% ethanol while gently dislodging pollen loads on the frons, thorax, and sternum with a dissecting needle. The dry pollen residue was stained and mounted in 1-2 drops of Calberla's fluid (Ogden et al., 1974). To prevent contamination of the body of an insect with pollen carried by another in the same jar, the bodies of insect specimens were isolated from each other by wrapping them in tissue. Insect distributions were determined from collections at the Natal Museum, Pietermaritzburg, and the South African Museum, Cape Town, plus our own observations and collections. Insect vouchers are deposited at the Natal Museum, Pietermaritzburg.

Nectar Analyses

Nectar volume measurements Table 2 were made from unbagged flowers in the field and represent the standing crop which will be influenced by visitation rates. Whole flowers were picked and nectar was withdrawn from the base of the floral tube with 3 ml capillary tubes after separating the ovary from the perianth (Iridaceae) or base of the hypnthium tube from the pedicel (Geraniaceae). Nectar was extracted from five or more individual per population in most cases Table 2. Nectar samples were dried on Whatmans filter paper no. 1 and sent to sent to B.-E. van Wyk, Rand Afrikaans University, Johannesburg, for analysis Table 2. The percentage of sucrose equivalents in fresh nectar was measured in the field on a Bellingham & Stanley hand-held refractometer (0-50%) from five or more individuals per population.

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