The water-vapour uptake system of the phthiraptera

The occurrence of active water-vapour uptake was examined in 16 Phthirapteran species representing the two groups of biting lice or Mallophaga (Amblycera and Ischnocera) and the sucking lice or Anoplura. Water-vapour uptake could not be demonstrated in the Anoplura and although it is frequently encountered in the biting lice, some members of both the Ischnocera and Amblycera lack the faculty. Uptake performance in the absorbing species of biting lice is exceptionally efficient showing higher rates and lower thresholds than other absorbing arthropods. The critical equilibrium humidities were found to range between 43 and 52% r.h., 43% being the lowest value so far reported. The uptake rates, expressed as a percentage of total body water mass, by far surpass those of all other arthropods investigated. The Phthirapteran uptake pattern closely resembles that of the Psocoptera, showing abrupt initiation and termination of the uptake process, limitation of continuous absorption to relatively short periods of time and constancy of the absorption rate over the entire period of continuous uptake. Studies on the uptake site and mechanism in Phthiraptera revealed an oral-uptake system which is congruous with that of the Psocoptera. The structural components of the uptake device, like a pair of oval lingual sclerites, representing the site of water-vapour condensation and a cibarial sucking pump which is connected by a paired or branching selerotized tubule to the lingual selerites and is responsible for the transfer of the condensed water to the gut, are unique acquisitions of the Psocodea.In those members of the biting lice which have lost the faculty of water-vapour uptake the structural components of the uptake system are modified or reduced.     

Water uptake in germinating pecan (Carya illinoinensis) seed

• Water uptake is the fundamental and essential requirement for seed germination. Pecan seed has a hard woody endocarp that plays an important role during water uptake.
• To explore water uptake during germination, the spatiotemporal pattern of water and effect of the endocarp were analysed using high-field MRI, dye-tracing, wax blocking and SEM of water uptake.
• Isolated seeds completed water uptake in 8 h while whole seeds required 6 days, hence, cracking the endocarp plays an important role. The hilum is the channel through which water enters the seed, while the remainder of the seed coat consist of cells covered with a waxy layer that act as a barrier to water absorption. The region with the highest water content in pecan seed is the edge of the U-shaped region, and water can progressively diffuse from this U-shaped region into the whole kernel.
• We report a new water absorption stage between phase II and phase III of the triphasic model of water uptake of pecan seeds. Cracking the endocarp changed water distribution in pecan seeds, which may trigger further water absorption and radicle elongation.

     

Occurrence,properties and biological implications of the active uptake of water vapour from the atmosphere in Psocoptera

Water vapour absorption is shown to occur in 22 species of Psocoptera inhabiting diverse environments and representing all major groups of this insect order. Evidently the faculty is a common feature of the whole order and it seems not to be related to specific environmental conditions. For the first time water vapour uptake could be demonstrated in fully winged and flying insects. The critical equilibrium humidities vary considerably among different species ranging from 58 to 85% r.h. Marked interspecific differences are also observed in water loss and uptake rates but no clear correlation with habitat or systematic group is recognizable. The uptake rates of Psocoptera are among the highest of all arthropods investigated so far. From weight recordings with a sensitive microbalance it could be seen that continuous operation of the uptake mechanism is restricted to limited periods of time of less than 1 hr regardless of the water status of the animals. Initiation and termination of the uptake process are abrupt and continuous uptake proceeds at a constant rate at a given relative humidity. Uptake rates are humidity-dependent decreasing with falling relative humidity whereas the adjustment of the equilibrium level of body water is independent of ambient humidity. Equilibrium is maintained by intermittent operation of the uptake mechanism within ca. 3% of body water mass. The uptake mechanism exhibits marked sensitivity to starvation in most members of the Psocomorpha. Some features of the uptake process of Psocoptera are in close agreement with those of Mallophaga reflecting the close relationship between the two groups.     

Passive exchanges during water vapour absorption in mealworms (Tenebrio molitor): a new approach to studying the phenomenon.

The weights of single mealworms were continuously recorded at 20 degrees C during exposure to periods of constant humidity and to abrupt changes in atmospheric vapour pressure. Two exchange stages were recognized in each animal. Weight changes were either limited to slow losses, suggesting transpiration through the external cuticle, or showed more rapid humidity-dependent gains as well as losses. Rapid exchanges indicated that water was gained or lost through permeable barriers, from a fluid compartmet of significantly lower vapour pressure than the haemolymph, equivalent to about 90% R.H. Weight gains and losses during humidity changes provided evidence of a significant, passively exchanging fluid compartment located between the exchange surface and absorbing mechanism. Weight changes in faecal pellets following their elimination provide further support for a rectal site of atmospheric absorption.     

根区交替控制灌溉条件下玉米根系吸水规律

为了阐明根区交替控制灌溉(CRDAI)条件下玉米根系吸水规律,通过田间试验,在沟灌垄植模式下采用根区交替控制灌溉研究玉米根区不同点位(沟位、坡位和垄位)的根长密度(RLD)及根系吸水动态。研究表明,根区土壤水分的干湿交替引起玉米RLD的空间动态变化,在垄位两侧不对称分布,并存在层间差异;土壤水分和RLD是根区交替控制灌溉下根系吸水速率的主要限制因素。在同一土层,根系吸水贡献率以垄位最大,沟位最低;玉米营养生长阶段,10—30 cm土层的根系吸水速率最大;玉米生殖生长阶段,20—70 cm为根系吸水速率最大的土层,根系吸水贡献率为43.21%—55.48%。研究阐明了交替控制灌溉下根系吸水与土壤水分、RLD间相互作用的动态规律,对控制灌溉下水分调控机理研究具有理论意义。     

Morphological factors of the central whorl leaf associated with leaf surface wetness and resistance in sorghum to shoot fly,Atherigona soccata*

Earlier studies showed that leaf surface water on the central whorl leaf of sorghum seedlings is associated with resistance to shoot fly. In this study, the results of an experiment to determine if leaf surface wetness (LSW) originates from atmospheric condensation or from the plant are described. Morphological structures: trichomes, stomata, leaf cuticle and quantity of surface wax of the central whorl leaf were also examined for their role in LSW production. The results suggest that LSW of the central whorl leaf originates from the plant and is not due to condensation of atmospheric moisture. The presence of trichomes was indirectly associated with LSW and resistance to shoot fly but stomatal density was not associated with LSW production. The amount of wax extracted per 100 mg of fresh weight varied significantly between genotypes and seedling age. It was more in susceptible than in resistant genotypes; however, cuticular thickness was not associated with resistance. It is suggested that LSW could be the result of some form of cuticular movement of water to the leaf surface.     

Tandem Recruitment and Trail Laying in the Ponerine Ant Diacamma rugosum: Signal Analysis1

During nest emigration, Diacamma rugosum scouts recruit female nestmates to the new nest site by tandem running. ♂♂, brood and prey objects are carried. The tandem leaders stimulate their nestmates to follow them by pushing or, more rarely, pulling them with the mandibles. The signals releasing the following behaviour are mainly chemical. Only 15–30% of motivated followers react positively to an odourless paper or wax dummy. The ♀♀ follow cut-off thoraces, legs and gasters plugged at the end or without hind gut and sting apparatus, just as well as a leading ant. The ants even follow a dummy consisting of body parts if they are not in direct mechanical contact with it. The leading effect of the body surface is not reduced by intensive cleaning with water or by extraction in solvents of different polarity. Only maceration in potash lye eliminates the leading effectiveness of the cuticula. None of the secretions of the tested abdominal glands release following behavior. Only the hind gut fluid possesses leading signal qualities. No distribution of faeces over the bodies of the leading ants can be observed before or during tandem running. The faecal pheromone responsible for this leading effect does not seep into the superficial layer of a leader dummy made from bee wax but it can be washed off with water. These results show that the actual signal releasing tandem following is an unspecific odour substance of the cuticula surface. The presence of the hind gut fluid is not necessary for the tandem following response. It may be an additional signal. During nest emigration the hind gut fluid is scattered patchily in the form of small droplets by the nest finders on their way to the new nest. No increased deposition of faecal droplets could be observed on the way to repeatedly visited rich food sources. The hind gut fluid serves as a long lasting trail substance and has an exclusively orienting effect. The secretions of the other abdominal glands are not trail pheromones. The nest entrance is marked colony-specifically.     

A comparison of the water balance characteristics of Typhlodromus occidentalis and Amblyseius finlandicus mites (Acari: Phytoseiidae) and evidence for the site of water vapour uptake

To determine how adult Typhlodromus occidentalis, a mite used in the biological control of spider mites, thrive in arid western North America, the water balance characteristics of adult females were compared to those of a laboratory colony of Amblyseius finlandicus originating from Finnish apple orchards. The mites contained comparable amounts of water (73.6 and 74.9%, respectively, for T. occidentalis and A. finlandicus), absorbed water from the air between 86% and 92% relative humidity (RH) (critical equilibrium humidity) and drank free water from droplets. Typhlodromus occidentalis were distinguished, however, by having lower net water loss rates (0.8% versus 1.3% h–1 at 0% RH, 20°C for A. finlandicus), a feature that enables them to retain water more effectively. Above the critical equilibrium humidity water was lost by adult female T. occidentalis whose mouth parts had been blocked with wax, implying an oral uptake mechanism for the absorption of water vapour. © Rapid Science Ltd. 1998     

Transpiration rate and intercellular diffusive resistance in the tobacco leaf

The increase in the measured transpiration rate in tobacco leaves due to the experimentally decreased humidity of the bulk air was found to be significantly lower than the theoretical value calculated from the change of water vapour concentration gradients. Boundary layer and stomatal diffusive resistances remained unchanged under experimental conditions with no change of net photosynthetic CO₂ uptake. This suggests an increase in intercellular diffusive resistance with an increase in water vapour concentration gradient which is the driving force of water vapour diffusive part of transpiration flux. The increase can be ascribed to the lengthening of intercellular diffusive pathway as steeper water vapour concentration gradient in intercellular spaces results in an increased evaporating surface of intercellular cells thus moving the effective plane of vaporization in leaf mesophyll further inwards. Due to different and independent changes of concentration gradients for water vapour and CO₂, different length of intercellular diffusive pathways for CO₂ and water vapour may be expected.     

The egg-shell of Drosophila melanogaster. VI, Structural analysis of the wax layer in laid eggs

Utilizing freeze-fracturing conventional electron microscopy and scanning electron microscopy methods, a wax layer was identified, sealing the oocyte of Drosophila melanogaster. In mature egg-shells wax forms a hydrophobic layer surrounding the oocyte and lying between, and in very close contact with the vitelline membrane (interiorly) and the crystalline intermediate chorionic layer (exteriorly). In cross-fractured views it is less than 50 A thick whereas in longitudinal fracturing it reveals smooth fracture faces of a multilayered material in the form of hydrophobic areas or plaques (0.5-1 microns in diameter) which are partially overlapping and highly compressed between the vitelline membrane and the innermost chorionic layer. The evidence for this layer being a wax are the facts that a) it is not preserved in conventional fat-extracting electron microscopy methods, b) it directs laterally the fracture planes during freeze-fracturing and reveals smooth fracture faces. Analysis of the structural features of wax in mature egg-shell in various species of Drosophilidae have shown that the wax layer exhibits indistinguishable (among the species) hydrophobic plaques, which have the same size and thickness with Drosophila melanogaster. These data provide structural evidence explaining the physiological resistance of the insect eggs studied, against water loss or water uptake, whenever they are laid on substrates with extreme environmental conditions. In addition, the data demonstrate how an extracellular substance can be organized to perform that function.     

Frontal bodies: Novel structures involved in water vapour absorption by the desert burrowing cockroach, Arenivaga investigata

Above 83% relative humidity, nymphs and adult females of the desert cockroach can condense water vapour on to a fluid layer covering protruded hypopharyngeal bladders. This fluid is produced by a pair of spheroidal bodies situated beneath the frons. Each such frontal body is connected by to the corresponding bladder by a groove in the epipharynx. During absorption, contraction of muscles connecting the frontal bodies to the frons causes them to move dorsally from the mandibles. Oscillation frequency increases with relative humidity or the application of nanoliter quantities of water to the bladders. Frontal bodies appear to be derived from invaginations of the integument, and consist of a mass of tough fibres containing protein and chitin. Fibres embed in a permeable plate which gives rise to the epipharyngeal groove. Tonofibrillae connect the fibres to elongate epidermal cells which are composed primarily of microtubules. The myoepidermal junction is characterized by fascia adherens. Frontal bodies resist tensile forces, but undergo changes in shape as they oscillate. Accompanying changes in hydrostatic pressure may move extracellular fluid across the plate and into the epipharyngeal groove. Possible roles of the fluid in the absorption process are discussed.     

Proteins adsorbed to a hydrophobic surface used for determination of proteolytic activity

Wettability of a thin layer of protein adsorbed to a hydrophobic surface is reduced after proteolytic digestion. Reduced wettability is demonstrated by condensation of water vapour on the surface. The condensation patterns of enzyme-treated and untreated protein layers give different light-scattering properties which can be observed by the naked eye. Based on these principles, a new simple and inexpensive method, thin layer enzyme assay (TEA), for determination of proteolytic activity, was developed. Fibrinogen, gammaglobulin (IgG), bovine serum albumin (BSA), haemoglobin, ovalbumin and gelatin were used as substrates. The proteolytic activity in 1 ng trypsin (EC 3.4.21.4) and in 1 ng pronase (EC 3.4.24.4) was reproducibly detected.     

Ultrastructure of the rectal sac, the site of water vapour uptake from the atmosphere in larvae of the oriental rat flea Xenopsylla cheopis

A portion of the hindgut of Xenopsylla cheopis larvae, the rectal sac, is extraordinarily enlarged and differentiated into a specialized organ displaying well-elaborated transporting epithelia. This organ is unique among insect recta because of gutter-like arrangement of two ultrastructurally distinct cell types with an asymmetrical position of the membranemitochondria complexes. The cells of the dorsal gutter have highly folded apical plasma membranes on the lumen side. The cells of the ventral gutter show deep infoldings of the basal plasma membrane on the haemolymph side. Less elaborate folds originate from the opposite sides of the cells. The nuclei of the dorsal epithelial cells are located in the basal part; those of the ventral cells in the apical portion of the cell. The ultrastructural features of the rectal sac, its ventilation synchronized with rhythmic opening of the anus during phases of active water vapour uptake, as well as the reversible arrest of uptake by experimental occlusion of the anus, reveal that condensation and uptake of atmospheric water take place in this organ.     

Using Soil Water Depletion to Measure Spatial Distribution of Root Activity in Oil Palm (Elaeis guineensis Jacq.) Plantations

Knowledge of where roots are active is crucial for efficient management of nutrients in tree crops but measurement of root activity is problematic. Measurement using soil water depletion is an approach that has not been tested in a humid climate. We hypothesised that the three dimensional distribution of root activity of a tree crop in the humid tropics (a) can be determined by measuring soil water depletion during rain-free periods, and (b) is influenced by environment (soil type and climate) and surface management. A field study was carried out in which soil water content was measured and water uptake calculated (by difference between soil water content at beginning and end of rain-free periods) for different surface management zones and depths (0.1 m intervals to 1.6 m depth) under oil palm (Elaeis guineensis Jacq.) at a loam–clay site and a sandy site. Significant differences were measured between sites and between surface management zones at each site. At both sites water uptake was highest under the weeded zone close to the palm stem, slightly lower under the zone where pruned fronds are placed, and lowest under the path used for removing harvested fruit. Vertical distribution of root activity differed between the sites, with higher activity near the surface at the finer textured site. Total water uptake values were lower than estimates of evapotranspiration made using climate data. The difference was probably largely due to water uptake from deeper than 1.6 m. This study showed that the spatial distribution of tree root activity in a humid climate could be quantified using a relatively simple method.     

Effects of Local Nitrogen Supply on Water Uptake of Bean Plants in a Split Root System

To study the effects of local nitrogen supply on water and nutrient absorption, French bean （Phaseolus vulgaris L.） plants were grown in a split root system. Five treatments supplied with different nitrogen forms were compared： homogeneous nitrate （NN） and homogenous ammonium （AA） supply, spatially separated supply of nitrate and ammonium （NA）, half of the root system supplied with N-free nutrient solution, the other half with either nitrate （NO） or ammonium （AO）. The results showed that 10 d after onset of treatments, root dry matter （DM） in the nitratesupplied vessels treated with NA was more than two times higher than that in the ammonium-supplied vessels. Water uptake from the nitrate-supplied vessels treated with NA was 281% higher than under ammonium supply. In treatments NO and AO, the local supply of N resulted in clearly higher root DM, and water uptake from the nitratesupplied vessels was 82% higher than in the -N vessels. However, in AO plants, water uptake from the -N nutrient solution was 129% higher than from the ammonium-supplied vessels. This indicates a compensatory effect, which resulted in almost identical rates of total water uptake of treatments AA and AO, which had comparable shoot DM and leaf area. Ammonium supply reduced potassium and magnesium absorption. Water uptake was positively correlated with N, Mg and K uptake.     

云南双蜡蚧蜡泌物的超微形态与化学成分

采用扫描电镜、红外光谱、气相色谱/质谱联用技术研究了云南双蜡蚧Dicyphococcus bigibbus Borchsenius（同翅目：蚧科）蜡泌物的超微结构和化学成分。结果发现：该虫的若虫与成虫分泌的蜡质从蜡腺排出初期均为湿蜡,在体外凝结形成质地稍硬而脆的玻璃状干蜡壳,蜡壳具有均匀脊和横层。幼期和雄性蜡壳小,船形,周缘带有蜡角,中央隆起。雌成虫蜡壳大,元宝形。蜡泌物的红外光谱吸收峰密集,峰型尖锐,种的特征明显。用红外光谱特征推断蜡泌物的主要基团和化学构成在GC/MS检测中得到印证。用甲酯化和非甲酯化两种处理方法检测证明,该虫蜡泌物主要成分是一系列高级的长链饱和与不饱和的烃、脂肪酸及酯类化合物。化合物的碳原子数从C₁₄～C₄₀,大部分为偶数个,特别是碳链长度在C₃₀～C₄₀的酯类化合物种类多,比例大。还将该蚧虫蜡泌物的特征与蚧科内近缘的蜡蚧属种类及瘤坚大球蚧、朝鲜毛球蚧、背刺毡蜡蚧、白蜡虫等作了对比,阐述了蜡泌物在蚧虫分类、系统学及防治中的意义。     

Variations in stream water uptake by Eucalyptus camaldulensis with differing access to stream water

The stable isotopes ²H and ¹⁸O were used to determine the water sources of Eucalyptus camaldulensis at three sites with varying exposure to stream water, all underlain by moderately saline groundwater. Water uptake patterns were a function of the long-term availability of surface water. Trees with permanent access to a stream used some stream water at all times. However, water from soils or the water table commonly made up 50% of these trees' water. Trees beside an ephemeral stream had access to the stream 40–50% of the time (depending on the level of the stream). No more than 30% of the water they used was stream water when it was available. However, stream water use did not vary greatly whether the trees had access to the stream for 2 weeks or 10 months prior to sampling. Trees at the third site only had access to surface water during a flood. These trees did not change their uptake patterns during 2 months inundation compared with dry times, so were not utilising the low-salinity flood water. Pre-dawn leaf water potentials and leaf ¹³C measurements showed that the trees with permanent access to the stream experienced lower water stress and had lower water use efficiencies than trees at the least frequently flooded site. The trees beside the ephemeral stream appeared to change their water use efficiency in response to the availability of surface water; it was similar to the perennial-stream trees when stream water was available and higher at other times. Despite causing water stress, uptake of soil water and groundwater would be advantageous to E. camaldulensis in this semi-arid area, as it would provide the trees with a supply of nutrients and a reliable source of water. E. camaldulensis at the study site may not be as vulnerable to changes in stream flow and water quality as previously thought.     

Water vapour uptake by diapausing eggs of a tropical walking stick

Abstract. This study is the first to demonstrate the capacity of an arthropod egg, that of a tropical walking stick Extatosoma tiaratum (Macleuy), to absorb water vapour from the air. This species diapauses both as an early embryo and then again as a pharate first instar larva, and both stages are capable of absorbing water vapour. Water vapour absorption occurs at lower humidities and at a lower rate for an egg in early embryonic diapause (c. a_v 0.30, 0.516 mg h^-1δ_v^-1) than in the diapausing pharate first instar (c. a_v 0.60, 0.725 mgh^-1δa_v^-1) at 25C. In addition to having the capacity to gain water at very low vapour activities, water is efficiently conserved as indicated by the low rate of water loss (0.015% h^-1 in the early embryo and 0.046% h^-1 in the pharate larva at 25C). Eggs that have been killed lose water when held at a hydrating vapour activity, thus implying that active uptake contributes to net absorption. Wax block experiments suggest that water is absorbed over the entire chorionic surface. Eggs of five other insect species that were examined [Lymantria dispar (L.), Bombyx mori (L.), Antheraea polyphemus (Cram.), Oncopeltus fasciatus (Dallas) and Diaferomera femorata (Say)] lacked the ability to absorb atmospheric water.     

Chemical composition of the epicuticular and intracuticular wax layers on the adaxial side of Ligustrum vulgare leaves

Previous research has shown that cuticular triterpenoids are exclusively found in the intracuticular wax layer of Prunus laurocerasus. To investigate whether this partitioning was species-specific, the intra- and epicuticular waxes were identified and quantified for the glossy leaves of Ligustrum vulgare, an unrelated shrub with similar wax morphology. Epicuticular wax was mechanically stripped from the adaxial leaf surface using the adhesive gum arabic. Subsequently, the organic solvent chloroform was used to extract the intracuticular wax from within the cutin matrix. The isolated waxes were quantified using gas chromatography with flame ionization detection and identified by mass spectrometry. The results were visually confirmed by scanning electron microscopy. The outer wax layer consisted entirely of homologous series of very-long-chain aliphatic compound classes. By contrast, the inner wax layer was dominated (80%) by two cyclic triterpenoids, ursolic and oleanolic acid. The accumulation of triterpenoids in the intracuticular leaf wax of a second, unrelated species suggests that this localization may be a more general phenomenon in smooth cuticles lacking epicuticular wax crystals. The mechanism and possible ecological or physiological reasons for this separation are currently being investigated.     

The Relation of Water Absorption by Wheat Seeds to Water Potential

The progress of water absorption by wheat grains was studiedby supplying water in the vapour phase, at controlled potentials. At a potential of –250 metres of water, the curve forwater uptake against time shows exponential approach to equilibriummoisture content. Living and dead seeds behave similarly untilgermination effects are apparent. Water uptake in the earlystages is probably due to physical rather than physiologicalprocesses. When germination occurs, it causes an exponentialincrease in the rate of water uptake. At higher potentials, up to zero, the uptake curves for deadseeds depart from the simple exponential relationship; in additionto the exponential component, there is a component the rateof which increases with time to a constant rate. The first componentmay represent the physical process of imbibition by the starch,and the second the initiation and progress of starch hydrolysis. A parameter a of the formula derived for the curves is interpretedas representing the diffusivity of water vapour in the seedmaterial, depending upon the physical properties and dimensionsof the seed.