Powdery Pollen Research Articles

BIOECOLOGY AND HARM OF WHITEFLIES AND PEST RISK ANALYSIS

Whiteflies are very small insects (1.5-2 mm), resembling microscopic moths. The wings and body are covered with white powdery pollen. They reproduce sexually, the eggs are attached to the underside of the leaves, on the stems. They hibernate in the puparia phase (pupa) on fallen leaves, in cracks and hollows of trees. The development is complicated: the larvae of the first age are mobile, the next stages are immobile. The larvae then develop into a pupa (puparium). One generation develops within 1 month. In greenhouses it can breed all year round and give 8-10 generations.

Flowers of Halgania (Ehretiaceae, Boraginales) are set up for being buzzed and the role of intertwining anther trichomes

Flowers that release their powdery pollen by being vibrated through buzzing are morphologically diverse and have evolved many times independently. Most prominently, buzz-pollination is known from Solanum (Solanaceae) defining the “solanoid” flower type by Knut Fægri. The flowers of buzz-pollinated, Australian Halgania resemble the actinomorphic Solanum floral architecture: The plants have a yellow anther cone with an apical pore, protruding from a widely funnel-shaped to rotate, blue to violet corolla. However, Fægri rejected the solanoid flower type for some of the Halgania species due to a contracted inflorescence, a funnel-shaped corolla or an ostensible lack of a female stage. Using light and scanning electron microscopy, we investigated traits referring to the floral architecture of Halgania and compared the flowers of different species. In all investigated species the anthers of the cone are connected via long, intertwined trichomes (denoted “capillinection”) both between the individual anthers and in the central stylar channel. The anther opening is functionally reduced to an apical pore by 1) capillinection and spatial compression of the thecal walls, leaving only small apical slits and 2) by anther appendages that unify the ten slits to a single pore. Halgania flowers are morphologically similar to each other and are buzz-pollinated. We conclude that they are all structurally and functionally matching the flowers of tomato, Solanum lycopersicum, and thus the concept of solanoid flowers as defined by Knut Fægri.

Pollination ecology of the Gray Nicker Caesalpinia crista (Caesalpiniaceae) a mangrove associate at Coringa Mangrove Forest, Andhra Pradesh, India

Caesalpinia crista L., commanly known as Gray Nicker, is an oligohaline mangrove associate confined to landward marginal areas of the Coringa Mangrove Forest, Andhra Pradesh, India. The flowering occurs during the wet season from June to November. The flowers are hermaphroditic, self-compatible and exhibit a mixed breeding system. The floral characteristics that constitute melittophilous pollination syndrome include diurnal anthesis, slight fragrance, zygomorphy, yellow petals, with a flag petal displaying a conspicuous nectar guide, and the presence of nectar with a high sugar concentration. Extra-floral nectar along the rachis is an additional attractant and is easily perceivable by bees. The plant is pollinated almost exclusively by bees, especially carpenter bees. The floral characteristics such as free petals, fully exposed stamens with dry and powdery pollen grains and hairy stigma facilitate anemophily which is effective due to high winds during the rainy season. The prolific growth and near synchronous flowering at population level contribute to pollen availability in huge quantities and enable anemophily as an effective mode of pollination. The functionality of melittophily and anemophily together constitutes ambophily. Hand-pollination experiments indicated that the plant is principally out-crossing. The natural fruit set does not exceed 10%; this lowest percentage could be partly due to flower-feeding by the beetle, Mylabris phalerata. The fruits are indehiscent, 1-seeded, which are buoyant and are not dispersed far away from the parental sites. The viable seeds produce new plants in the vicinity of parental plants during the rainy season. This plant builds up its population as small patches or in pure stands and hence is important in building landward mangrove cover.

Pollination Ecology of Himalayan Sea Buckthorn, Hippophae rhamnoides L. (Elaeagnaceae)

Fruits of Hippophae rhamnoides (Elaeagnaceae), commonly known as sea buckthorn or Leh-berry in India, constitute an important source for many medicinal and nutritional products. As the species is of high economic value, attempts are being made to establish commercial plantations for a sustainable supply. There is hardly any information on pollination ecology of this species, which is necessary for establishing and managing commercial plantations. We studied the floral biology and pollination ecology in natural populations of the species growing at Leh-Ladakh. H. rhamnoides is dioecious and exclusively wind-pollinated. The male flowers produce an enormous amount of dry, powdery pollen grains that remain viable for up to 48 h. The pollen flow in the air from the source is confined to 15 m. The female flowers are uniovulate. In nature, about 60% of the female flowers get pollinated with an average stigmatic pollen load (± SE) of 9.49 ± 0.76. For optimal plantation conditions, it is suggested that a male plant must be inter-planted within 10-15 m of the female plants for effective natural pollination.

Dual deceit in pseudopollen-producingMaxillaria s.s.(Orchidaceae: Maxillariinae)

Most species of Maxillaria s.l. are rewardless and employ deceit pollination strategies. Some, however, reward pollinators with nectar, resins or pseudopollen (farina). Pseudopollen is yellow–white in colour and is usually composed of food-laden cells formed by detachment or fragmentation of moniliform labellar hairs. As the pollen of epidendroid orchids is bound in pollinia, it is not accessible to pollen-foraging insects. It has thus been proposed that potential insect pollinators, deceived by the resemblance of pseudopollen to the nutritious, powdery pollen of other angiosperms, gather it and feed it to their larvae. Mimicry here, however, may not be as simple as supposed. This study compares the pseudopollen of selected species of Maxillaria s.s., namely Maxillaria grandis, M. grayi, M. huebschii and M. roseola (all members of the M. grandiflora complex), M. lepidota (M. arachnites complex) and M. buchtienii (M. splendens complex), using light microscopy (LM), fluorescence microscopy, histochemistry, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and comments on its evolutionary significance. Some members of the M. grandiflora complex produce pseudopollen-forming hairs, the cells of which contain potential food rewards in the form of an intravacuolar protein body and abundant starch grains. Others produce pseudopollen that is devoid of protein bodies, but contains abundant starch, and others produce pseudopollen that lacks protein bodies and contains negligible amounts of starch. Maxillaria lepidota and M. buchtienii fall into the second and third categories, respectively. Lipid droplets, when present, usually occur in minute quantities. These observations suggest that a dual deceit strategy operates in some species, as pseudopollen not only mimics powdery pollen, but in many instances lacks a food reward. Cryptic evolutionary changes to pseudopollen content may confer biological advantage by reducing expenditure of material and energy in food reward production, while trichome micromorphology simultaneously encourages pollinator visits. The presence or absence of particular foods may, in turn, result in pollinator selection. Conversely, in the absence of food rewards, insect behaviour is unlikely to be reinforced, possibly to the detriment of the orchid. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173, 744–763.

The structure and function of orchid pollinaria

Cohesive masses of pollen known as pollinia have evolved independently in two plant families — Orchidaceae and Asclepiadaceae. Yet, the bilateral symmetry of orchids has allowed a greater degree of specialization in pollination systems and a much greater diversity in the morphology of pollinaria — units comprising the pollinia(um) together with accessory structures for attachment to the pollinator. Pollinaria differ in the degree of cohesion of pollen in the pollinium, which may be soft, sectile (comprised of sub-units known as massulae) or hard. A single hard pollinium may contain more than a million pollen grains, yet pollen:ovule ratios in orchids are several orders of magnitude lower than in plants with powdery pollen due to the lack of wastage during transport to the stigma. Attachment of pollinia to the pollinator is usually achieved by means of a viscidium that adheres most effectively to smooth surfaces, such as the eyes and mouthparts of insects and beaks of birds. The stalk connecting a pollinium to the viscidium may be comprised of a caudicle (sporogenous in origin) and/or a stipe (derived from vegetative tissue), or be lacking altogether. Caudicles and stipes may undergo a gradual bending movement 20 s to several hours after withdrawal from the flower, the main function of which appears to be to reduce the possibility of geitonogamous pollination. Other mechanisms that promote outcrossing and pollen export in orchids include pollen carryover (achieved by sectile or soft pollinia), temporary retention of the anther cap, protandry and self-incompatibility (rare among orchids). Pollinaria ensure that large pollen loads are deposited on the stigma, thus enabling the fertilization of the large numbers of ovules in the flowers of Orchidaceae. Pollinaria also ensure efficient removal of pollen from the anther, minimal pollen wastage during transit, and a high probability of deposition on conspecific stigmas.

Floral structure and development of Ceratiosicyos laevis (Achariaceae) and its systematic position

The morphology and development of the flowers of Ceratiosicyos laevis (Achariaceae) were investigated. Plants are monoecious and the inflorescence is a thyrse composed of a single female flower and two male cymose partial inflorescences. The sympetalous flowers of both sexes have an unusual urceolate shape. In young buds the free parts of the petals are postgenitally united. Before anthesis the fusion is ruptured but the petals remain coherent due to marginal cilia. Nectary-like bodies situated at the floral base seem to stabilize the shape of the flower additionally. The anthers are coherent by interlocking epidermal cells and form a narrow tube. They lack an endothecium. In anthesis only the style and the anther tube respectively protrude out of the flower. The synorganization of the anthers, the powdery pollen and the lack of an endothecium are suggestive of a buzz pollination syndrome. Some characters point to an affinity of Achariaceae with Cucurbitaceae. However, the family seems to be more closely related to Passifloraceae.

Floral structure and development of Ceratiosicyos laevis (Achariaceae) and its systematic position

The morphology and development of the flowers of Ceratiosicyos laevis (Achariaceae) were investigated. Plants are monoecious and the inflorescence is a thyrse composed of a single female flower and two male cymose partial inflorescences. The sympetalous flowers of both sexes have an unusual urceolate shape. In young buds the free parts of the petals are postgenitally united. Before anthesis the fusion is ruptured but the petals remain coherent due to marginal cilia. Nectary-like bodies situated at the floral base seem to stabilize the shape of the flower additionally. The anthers are coherent by interlocking epidermal cells and form a narrow tube. They lack an endothecium. In anthesis only the style and the anther tube respectively protrude out of the flower. The synorganization of the anthers, the powdery pollen and the lack of an endothecium are suggestive of a buzz pollination syndrome. Some characters point to an affinity of Achariaceae with Cucurbitaceae. However, the family seems to be more closely related to Passifloraceae.

Vibratory Collection of Actinidia deliciosa (Kiwifruit) Pollen

Dry, powdery pollen grains were expected from 'buzz pollinated' flower species. However, vibration of Actinidia deliciosa (kiwifruit) anthers (a buzz pollinated species) by a mechanical shaker, at similar vibrations to Bombus terrestris caused clumps of pollen joined by small droplets of tapetal fluid to be ejected. Pollen that was largely covered with tapetal fluid could not be removed by vibration, whereas dehydrated pollen was easily removed, even without vibration. The late desiccation of A. deliciosa anthers after anthesis meant that pollen removed by vibration depended on the anther maturity. The presence of the droplets gives insects which vibrate while foraging advantages over insects which do not. A vibration attachment on a commercial pollen harvester increased the weight of pollen collected by 57% over the whole day; 91% in the afternoon.

Insect-induced wind pollination of the palm Chamaedorea pinnatifrons and pollination in the related Wendlandiella sp.

In Peruvian Amazonia pollination ecology of two palms, Chamaedorea pinnatifrons (Jacq.) Oerst. and Wendlandiella sp. was studied from October 1988 to January 1990. Both palms are dioecious understory species that form locally dense populations. In C. pinnatifrons both sexes flower synchronously during the dry season. Prior to anthesis, the pendulous male inflorescence is inhabited by numerous thrips (Thysanoptera) and Ptiliidae (Coleoptera). Staminate flowers open by a small basal slit between the petals. At anthesis pollen is shed and the movements of the insects inside the flowers trigger pollen release in small clouds. Thus, the powdery pollen becomes airborne and finally air currents act as a vector, carrying pollen to the inconspicuous female plants, which usually are not visited by insects. The term ‘insect induced wind pollination’ is suggested for this pollination mode. Wendlandiella flowers during four months in the dry season. Male and female plants were not visited by insects. The dry condition of the pollen indicates that anemophily is the pollination mode in Wendlandiella. Fructification is rare but the plants show intense vegetative propagation. The significance of anemophily in the tropical lowland rain forest is discussed.

Floral Biology of Mallotus oppositifolius (Euphorbiaceae)

The unisexual flowers of Mallotus oppositifolius show a combination of entomophilous and anemophilous characteristics. They are visited by many species of short-tongued bees, but the powdery pollen is also presumably capable of wind dispersal. The female flowers offer no rewards to bees; it is therefore suggested that their resemblance to the pollen-yielding male flowers may cause bees to visit them in error. A NUMBER OF PLANTS OF THE TROPICAL FOREST UNDERSTORY have flowers that display combinations of characters normally associated with anemophily, such as light, smooth pollen, a high ratio of male to female flowers, and reduction of the attractive parts. However, air movement in the lower layers of the forest is very slight (Haddow and Corbet 1961), and it seems unlikely that pollen could be reliably transported for any distance (Faegri and van der Pijl 1971). Some forest Gramineae are visited and probably pollinated by insects (Soderstrom and Calderon 1971), and some forest Cyperaceae are visited by slugs (Lorougnon 1973). There are few published observations of pollination in such woody families as Euphorbiaceae that are frequent in the forest understory, particularly in disturbed places This paper reports observations on the common understory and forest edge shrub Mallotus oppositifolius (Geisel.) Muell. Arg. The observations were made in March 1977, at the beginning oif the rainy season, at the Agricultural Research Station of the University of Ghana, at Kade (60 09' N, 0? 55' W). The plants were growing at the edge of Moist Semi-deciduous forest (Hall and Swaine 1976). Five male and female inflorescences of various ages, giving a total of 220 flowers, were marked with numbered tags and observed each day.

The fine structure of the exine in relation to the stickiness of angiosperm pollen

The variable stickiness of entomophilous (mostly sticky) and anemophilous (always powdery) pollen always depends on the particular distribution and consistency of the pollenkitt on the pollen surface and is related to the fine structure of the exine. Two different “strategies” in exine evolution following the trend from entomophily towards anemophily are significant: 1. (1) Pollen grains without a tectum: the sticky pollen results mainly from the deposition of a great amount of homogeneous, mostly electron-dense pollenkitt between the columellae — so the sporoderm becomes incrusted with pollenkitt. In contrast powdery pollen results mainly from the deposition of a tiny amount of mostly heterogeneous, usually electron-transparent pollenkitt between the columellae, while a considerable amount of pollenkitt remains on the loculus wall. 2. (2) Pollen grains with a tectum: the sticky pollen results mainly from the attachment of a moderate amount of usually electron-dense, homogeneous pollenkitt on the tectum surface, while pollenkitt also enters into the exine cavities. In contrast powdery pollen results mainly from the deposition of an always heterogeneous, usually electron-transparent pollenkitt as a thin film covering parts of the tectum surface, while a great deal of an inhomogeneous, but mostly electron-dense pollenkitt fills up the exine cavities. In both cases the characters of “amphiphilous” pollen hold the balance between the extremes with respect to pollen stickiness, to the homogeneity and electron-density of pollenkitt and the mode of its distribution on the pollen surface.

Entwicklungsgeschichte und Ultrastruktur von Pollenkitt und Exine bei nahe verwandten entomo- und anemophilen Angiospermen: Salicaceae, Tiliaceae und Ericaceae

The characteristics of pollen cementing (stickiness; total amount, structure and distribution of the pollenkitt; fine structure of the exine) have been studied in Salix caprea, Populus nigra and P. tremula (Salicaceae), Tilia platyphyllos and T. tomentosa (Tiliaceae) , and Erica herbacea, Calluna vulgaris and Andromeda japonica (Ericaceae) . The homogeneous, electron-dense pollenkitt of S. caprea fills up the interbacular caves completely and is also situated on the outside layer of the exine; so the pollen is sticky and insectpollination is dominating. In contrast the also homogeneous, mostly electron-dense pollenkitt of P. nigra and P. tremula remains largely in the loculus, while only a little moves to the exine caves; the tectum is free of pollenkitt; so the pollen is powdery and the result is pollination by wind. In T. tomentosa and T. platyphyllos the mostly electron-dense (in part also foamy) pollenkitt is located preferably in the caves, but also in small amounts on the outer layer of the exine; so the pollen is only of medium stickiness, and pollination by insects and by wind is possible. In E. herbacea, C. vulgaris and A. japonica there is no pollenkitt sensu stricto at all: in the loculus tapetum-borne irregular globuli do not adhere on the exine; their nature remains obscure; there are no viscin-threads at all. Because of the “Streukegel”-mechanism the powdery pollen of the described Ericaceae allows pollination by wind.