Fly Pollination Research Articles

Pollination of the edelweiss, Leontopodium alpinum

Abstract This paper describes the pollinators, scent and nectar composition of the edelweiss ( Leontopodium alpinum ). In contrast to former statements in the literature, the flowers of this famous plant are frequently visited by various insects in 29 families. However, in the two populations of L. alpinum investigated here, flies (Muscidae) were the most frequent visitors. Although the investigated insects carried pollen grains all over their bodies and qualify as mess and soil pollinators, pollen grains were not randomly distributed on the bodies of the insects but were most conc ntrated on their legs. Their loads of L. alpinum pollen varied greatly, but more than 60% of all Leontopodium pollen grains found on the insects were carried by only 12% of the specimens collected, suggesting that a small fraction of the visitors is responsible for most of the pollen transfer. The number of pollen grains found on the insects also increased significantly with increasing body size of the insects. The scent of the flowers is sweet and honey-like (phenylethyl alcohol and phenylacetic acid) but also contains disagreeably smelling, sweat-like components (3-methyl-2-pentenoic acids, butyric acid and other fatty acids). Nectar is secreted in minute amounts in the tiny florets of the flower heads. The sugar composition of the nectar is dominated by the hexoses fructose and glucose. It also contains a high amino acid concentration with many different amino acids. Nectar, scent and the shape of the flowers of L. alpinum all fit the syndrome of fly pollination.

Phenological studies of shrub and treelet species in tropical cloud forests of Costa Rica

ABSTRACT(1) During 1978–1981, marked individuals of 107 species of treelets and shrubs in three forest types between 1300–1650 m elevation at Monteverde, Costa Rica, were monitored at monthly intervals for behaviour of leafing, flowering, and fruiting.(2) Although there was not a pronounced seasonal pattern of leafing activity, more species produced new leaves in the dry season. Species that flush large quantities of new leaves do so more commonly in the drier months. Leaf loss was gradual and unobtrusive in species observed.(3) Flowering activity was greatest in the late dry season and early wet season. Most species exhibited extended flowering; only 15% of the species were massively flowering. Massive flowerers showed less seasonality than extended flowerers.(4) Of the species studied, the majority had relatively unspecialized flowers which were visited by a variety of insects; small bee-pollination was the next most common, followed by hummingbird, beetle, settling moth, sphingid, butterfly, large bee and fly pollination (the pollination system of 18 species was unknown). Hummingbird pollinated species showed little seasonality of flowering when compared with species exhibiting small moth, and beetle pollination syndromes, as well as those with unspecialized flowers.(5) The vast majority of species studied have fleshy fruits (sarcochores). Fruiting activity was less markedly seasonal than flowering. Species with fruit are more numerous in the second half of the year (the wet season and early dry season). The second year of the study saw substantially fewer species in fruit than the first year; this is attributed to the greater than usual rainfall and inclement weather during the peak flowering season.(6) Cloud forest shrub and treelet phenology is compared with patterns of other forests that have been studied. In general, the greater the rainfall, the less seasonality of flowering and fruiting is seen. Although Monteverde is very wet, rainfall is intermediate between that of lowland dry and lowland wet forest in Costa Rica. Seasonality of flowering and fruiting at Monteverde is more pronounced than at La Selva (wet) and less obvious than in Guanacaste (dry).

Pollinator Sharing and Seed Set of Stellaria pubera: Competition for Pollination

I used field experiments to examine the effect of pollinator sharing on seed set in the understory herb Stellaria pubera. In piedmont North Carolina the solitary bee and fly pollinators of this species are also frequent visitors to Claytonia virginica. Removals of nearby flowers of C. virginica increased seed set of S. pubera. Examination of seed set in populations of potted plants indicated that the effect was due to change in species composition rather than plant density. Variation in seed production was high, however, and even when flowers were provided with excess pollen through supplemental hand pollinations, only 20% of ovules produced seeds. Competition for pollination appears to be one of several selective forces that act on blooming time of S. pubera. Stellaria pubera blooms slightly later than C. virginica. Whereas the seeds set of early flowers was increased 13% by removal of C. virginica and 19% by hand pollination, seed set of late flowers was unaffected. Plants forced to bloom early also tended to be more pollinator—limited than control plants. Removal of C. virginica did not, however, increase the seed set of S. pubera plants forced to bloom early significantly more than that of control plants. Other forces are probably also involved in the maintenance of blooming time.

Onion pollination by blowflies and honeybees in large cages

SUMMARYThree experiments to investigate the effect of pollination by blowflies (Calliphora and Lucilia spp.) and honeybees (Apis mellifera) on seed yield and crossing level were made using a mixture of plants from two open‐pollinated cultivars of onions (Allium cepa) in breeders' cages.No consistent differences were found between pollinators. In two experiments, fly pollination gave significantly higher yields than bee pollination but in the third, bee pollination gave slightly more seed. Crossing between cultivars, assessed by progeny testing on one cultivar, varied between 22‐7 and 55‐9%. Differences in crossing level attributable to the pollinators were not consistent and were not or only just statistically significant, but there were significant and substantial differences between the experiments themselves. Where more umbels were produced by the red‐bulbed cultivar than by the yellow, higher crossing levels were found in the yellow cultivar. The highest crossing levels were found in the only experiment where insects were not introduced until peak flowering time, but where seed yield was comparatively low. Crossing levels were lowest where the umbel numbers were approximately equal.Individual umbels studied showed that while seed set was usually heaviest at and just before the mid‐flowering date, this period could correspond with the lowest levels of crossing during the flowering period, particularly if flowering of the two cultivars was not completely synchronous.In field plots, approximately 75% of crossed seeds sown survived to give harvestable bulbs, but fewer than 50% of selfed seeds did so. In an experiment in which crossing levels from different pollinators were similar but survival levels differed significantly, it was deduced that bees performed more crossing within a cultivar than flies.

The role of dark flowers in the pollination of certain umbelliferae

Summary The dark purple flower in the umbel of Daucus and the black spot on the umbel of Artedia have been shown to play a significant role in the pollination of these umbelliferae, because they attract the fly pollinators by their mimicry of resting insects.

FLORAL STRUCTURE AND EVOLUTION IN LOPEZIEAE (ONAGRACEAE)

The Lopezieae present an interesting mixture of ancestral and derived characters: some members of the tribe retain the basic onagraceous chromosome number (n = 11), but the flowers are advanced in that they are mostly zygomorphic and always have a two‐merous androecium. Species differ in the position of the nectaries, also in the way in which floral parts are united above the inferior ovary. These differences, when analyzed with information from a new monograph of the Lopezieae, provide the basis for a phylogenetic tree. It is inferred that ancestral Lopezieae were bird‐pollinated woody perennials with regular flowers, two fertile stamens, and no floral tube distal to the ovary. Evolutionary events accompanying the emergence of modern taxa included abortion of the abaxial stamen (all surviving Lopezieae except Lopezia lopezioides), development of an epigynous floral tube (L. riesenbachia, L. semeiandra), decrease in floral symmetry without conversion to insect pollination (in two independent lines), and decrease in floral symmetry with conversion to insect pollination (in at least two independent lines). The prominent tubercles on upper petals of certain insect‐pollinated species apparently evolved from the less prominent swollen areas still present in some of the bird‐pollinated species. The tubercles and an associated snapping mechanism arose in response to increasing selection for fly pollination. Densely staining areas in some specimens may be osmophores; if so, scent plays a supplementary role in the orienting of insects to the upper petals. Interstaminal nectaries and the absence of a floral tube link the Lopezieae to Ludwigia; the relationship of these two taxa to Epilobium is presently unclear. Fossil records indicate that the Onagraceae had evolved by the beginning of the Tertiary Period and that the Ludwigia line is very old. The family's ancestral features are retained to a greater degree in Fuchsia, however, than in Ludwigia.

Floral Structure and Evolution in Lopezieae (Onagraceae)

The Lopezieae present an interesting mixture of ancestral and derived characters: some members of the tribe retain the basic onagraceous chromosome number (n = 11), but the flowers are advanced in that they are mostly zygomorphic and always have a two-merous androecium. Species differ in the position of the nectaries, also in the way in which floral parts are united above the inferior ovary. These differences, when analyzed with information from a new monograph of the Lopezieae, provide the basis for a phylogenetic tree. It is inferred that ancestral Lopezieae were bird-pollinated woody perennials with regular flowers, two fertile stamens, and no floral tube distal to the ovary. Evolutionary events accompanying the emergence of modern taxa included abortion of the abaxial stamen (all surviving Lopezieae except Lopezia lopezioides), development of an epigynous floral tube (L. riesenbachia, L. semeiandra), decrease in floral symmetry without conversion to insect pollination (in two independent lines), and decrease in floral symmetry with conversion to insect pollination (in at least two independent lines). The prominent tubercles on upper petals of certain insect-pollinated species apparently evolved from the less prominent swollen areas still present in some of the bird-pollinated species. The tubercles and an associated snapping mechanism arose in response to increasing selection for fly pollination. Densely staining areas in some specimens may be osmophores; if so, scent plays a supplementary role in the orienting of insects to the upper petals. Interstaminal nectaries and the absence of a floral tube link the Lopezieae to Ludwigia; the relationship of these two taxa to Epilobium is presently unclear. Fossil records indicate that the Onagraceae had evolved by the beginning of the Tertiary Period and that the Ludwigia line is very old. The family's ancestral features are retained to a greater degree in Fuchsia, however, than in Ludwigia.

POLLINATION BIOLOGY OF NEMOPHILA MENZIESII (HYDROPHYLLACEAE) WITH COMMENTS ON THE EVOLUTION OF OLIGOLECTIC BEES.

The interaction between plants and extremely diverse habitats and environmental conditions of California has resulted in rapid evolution in many plant groups. A small number of studies suggest that evolution in many of these groups has been accompanied and perhaps paralleled by evolution in particular groups of bees (Linsley and MacSwain, 1957, 1959; Linsley et al., 1963a, 1963b; 1964; Thorp, 1969). The interaction between these bees and their pollen plants is oligolectic. An oligolectic relationship is defined by Linsley and MacSwain (1957, 1958) as one . . in which the individual members of the population, throughout its range and in the presence of other pollen sources, consistently and regularly collect pollen from but a single plant species or from a group of similar or related plant species, turning to other sources, if at all, only when there is a local shortage or absence of that pollen. Oligolectic relationships may be nonselective or co-evolved. Included in the first class are Andrena linsleyi Timberlake, which collects pollen of Oenothera deltoides Torr. and Frem. in the morning after sphinx-moths have pollinated the flowers (Linsley et al., 1963; Gregory, 1964), and Andrena nemophilae Ribble which is discussed below. Such a bee must adapt to the evolutionary vicissitudes of the flower and its pollinator(s). The second class includes those bees which are pollinators of the host plant. Thus they may influence the evolution of the plant as well as being influenced by the plant. This group of bees and their pollen plants are of particular interest to the student of pollination biology and evolution. Although a number of studies have dealt with oligolectic bees, the basis of the relationship remains an enigma. The flight period of most oligolectic bees is short and the adult bee's only previous contact with a particular pollen source is the pollen and nectar it consumed as a larva. Three explanations have been suggested to explain oligolecty. First, it is genetically controlled (Thorp, 1969). Second, a preimaginal conditioning from the pollen and nectar that the larva consumes (Linsley, 1958). Third, some combination of the above, i.e., genetical control modified by conditioning (Thorp, 1969). In this paper my objectives are (1) to present a broad picture of the plant Nemophila menziesii H. and A. s.l. and its pollinators and (2) to re-examine particular questions concerning evolution within oligolectic bees. Specifically, I discuss the distribution, floral behavior and breeding system of the plant, Nemophila as a bee plant, the oligolectic Nemophila bees, the role of polylectic bees in pollination, and fly pollination. In the final section I discuss host plant recognition and evolution in oligolectic bees

Effect of Flower Thrips on Onion Seed Plants and a Study of Their Control

Feeding injury by the flower thrips, Frankliniella occidentalis (Pergande), to onion seed plants occurs primarly in the flower filaments, causing a premature loss of pollen, and a decrease in pollination and seed set. Microscopic examinations and counts show that about 10 thrips per flower or floret are needed to cause meaningful injury. Thus, an average of 9,000 to 10,000 thrips per seed head would be necessary to cause any economic injury and seed loss, at an average of 900 to 1000 flowers per head. Field investigations of thrips damage were conducted by introducing varying numbers of adults on seed heads enclosed by fine-meshed cloth cages. The highest infestations of nymphs plus adults attained were 1900, 2400, and 3600 per head. These numbers of thrips did not cause any reduction in the seed set, yield, size or viability. Thrips increased pollination and seed set over the controls in all experiments. The addition of pollinators resulted in an increased seed production and viability over that of thrips alone. The presence of fly pollinators and 2 heads per replicate cage proved necessary to obtain adequate seed set in the thrips-damage studies. Three years of experimentation never demonstrated enough thrips per head to cause an economic loss of onion seed. Two and three applications of parathion and diazinon resulted in satisfactory thrips control. These treatments did not increase or decrease seed set or yield but the use of parathion indicated some increase in seed viability. Parathion treatments reduced numbers of bee and fly pollinators for about 3 days when applied during bloom. A single prebloom application of 1/2-1 lb per acre of dimethoate gave outstanding thrips control and no pollinators reduction. Another application during bloom reduced pollinators for up to 10 days. The single dimethoate application resulted in an increase in seed set and yield, which appeared to be in addition to any possible effect on thrips and pollinators, indicating some additional plant response to the chemical.