Mouthparts of the bark beetle (Ips acuminatus) as a possible carrier of pathogenic microorganisms

The bark beetle Ips acuminatus Gyllenhal (Coleoptera: Curculionidae: Scolytinae) has been recently reported as one of the most serious secondary pests of pine trees. Since the adult beetles chew the sapwood to create tunnels, they have developed effective drilling mouthparts enough to make galleries directly into the heartwood of the tree. The mouthparts of this bark beetle exhibit typical morphology of mycophagous coleopteran beetles and have those characteristics of chewing mouthparts. Both maxillary and labial palpi have the functions of directing the food to the mouth and holding it while the mandibles chew the food. Although this bark beetle did not have prothoracic mycangial cavities, yeast-like spores were concentrated at the invaginated surface of mouthparts where cuticular hairs are densely packed. In particular, the cuticular surface around the base segments of these palpi has sufficient spaces to accommodate microorganisms during the series of drilling or feeding processes. Therefore, this paper reports detailed observation of the cuticular structure of the mouthpart using the field emission scanning electron microscopy (FESEM) for the purpose of demonstrating its possible implication to act as external carriers of pathogenic microorganisms.     

Mouthparts of larvae of Opifex fuscus and Aedes australis (Diptera: Gulicidae); a scanning electron microscope study

Abstract

Larvae of the New Zealand culicid species Opifex fuscus and Aedes australis have previously been reported to show dimorphism in the structure of their labral brushes, some larvae having pectinate bristles and others only simple hairs. In the scanning electron microscope all larvae showed some degree of pectination of hairs in these brushes. There is also a gradation in the pectination. Some bristles are only sparsely pectinate; because the dimensions of their teeth are close to the limit of resolution by the compound microscope, the pectination had previously gone undetected. The mouthparts of both species are intermediate in character between those typical of filter-feeding larvae and those typical of browsing larvae. The SEM appearance of maxillary sensoria and bristles on the ventral surfaces of the mandibular brushes is described; the latter bristles comb food particles out of the labral brushes and towards the mouth. Features of the mouthparts are illustrated with scanning electron micrographs.     

The mouth apparatus of Lithodes maja (Crustacea: Decapoda) – form,function and biological role

Being able to utilize many different food resources is probably an important aspect of the success of decapod crustaceans which fill a wide range of various ecological niches worldwide. The phenomenon is facilitated by the complex mouth apparatus found in this group, whose representatives possess six pairs of mouthparts– mandibles, maxillae 1, and maxillae 2 and three maxillipeds, the first three pairs of thoracic appendages which are also specialized to food manipulation. These six pairs are able to perform a number of movements for transporting, aligning, crushing and cutting. Studies into the functional morphology of mouthparts have already been carried out in some decapod species. This study focuses on Lithodes maja, a species of the hitherto understudied king crabs (Lithodidae), chosen on the grounds of their remarkable evolutionary history as ‘derived hermit crabs’. Individuals were filmed while being presented with different kinds of food. To obtain structural information on the individual mouthpart elements as naturally arranged in relation to one another, the shape of the mouthparts was 3D‐reconstructed from micro‐CT scans. These data were complemented by scanning electron microscopy, to analyse the surface structures in detail. There is evidence that the various elements of the mouthparts of L. maja can be sorted into six functional groups: (i) transporting mouthpart elements, (ii) aligning/sorting mouthpart elements, (iii) clutching/holding mouthpart elements, (iv) tearing/cutting/crushing mouthpart elements, (v) current‐generating mouthpart elements and (vi) grooming mouthpart elements. According to our 3D reconstruction, there only seem to be minor differences in morphology and relative position between the mouthparts of L. maja and those of the closely related species, Pagurus bernhardus.     

Functional anatomy of the hypopharynx and the salivary pump in the feeding apparatus of the assassin bug Rhodnius prolixus (Reduviidae, Heteroptera)

Focussing on the blood-feeding reduviid Rhodnius prolixus, we investigated the structure and function of the hypopharynx in (1) conducting the saliva towards the mouthparts and (2) bringing together the salivary pump and the stylets to ensure the difficult task of supplying the two closed antidromic streams of blood and saliva, while allowing the mouthparts to be moved forth and back during the feeding process. The distal apex of the hypopharynx forms a needle-like structure that is X-shaped in cross section. It arranges the interlocking of the maxillae in a manner resembling the fixed slider of a zip-lock. Further proximal, the hypopharynx extends into the maxillary food channel as a wide tongue. The salivary pump possesses two separate efferent ducts. The dorsal duct originates in the retrograde angle of the cupula (part of the salivarium) and conducts saliva directly into the maxillary salivary channel. The ventral duct originates at the distal opening of the cupula. It extends into a bag, the distal opening of which can be closed by a ventral bolster-like cuticle and opened by muscles. We show for the first time for heteropteran mouthparts that the saliva is not exclusively discharged into the maxillary salivary channel (via the dorsal efferent duct of the salivary pump), but that a large amount of saliva directly flows into the tube of the labium (via the ventral efferent duct of the salivary pump), which encloses the piercing stylets. However, within a short section, saliva may also pass from the ventral salivary duct into the maxillary salivary channel. Similar double salivary efferent ducts are present in the reduviids Triatoma dimidiata, T. infestans, Dipetalogaster maxima, Panstrongylus megistus, in the pyrrhocorid Pyrrhocoris apterus, and in the pentatomid Troilus luridus. It might thus be a more common feature of the Heteroptera.     

Functional morphology of the feeding apparatus and evolution of proboscis length in metalmark butterflies (Lepidoptera: Riodinidae)

An assessment of the anatomical costs of extremely long proboscid mouthparts can contribute to the understanding of the evolution of form and function in the context of insect feeding behaviour. An integrative analysis of expenses relating to an exceptionally long proboscis in butterflies includes all organs involved in fluid feeding, such as the proboscis plus its musculature, sensilla, and food canal, as well as organs for proboscis movements and the suction pump for fluid uptake. In the present study, we report a morphometric comparison of derived long‐tongued (proboscis approximately twice as long as the body) and short‐tongued Riodinidae (proboscis half as long as the body), which reveals the non‐linear scaling relationships of an extremely long proboscis. We found no elongation of the tip region, low numbers of proboscis sensilla, short sensilla styloconica, and no increase of galeal musculature in relation to galeal volume, but a larger food canal, as well as larger head musculature in relation to the head capsule. The results indicate the relatively low extra expense on the proboscis musculature and sensilla equipment but significant anatomical costs, such as reinforced haemolymph and suction pump musculature, as well as thick cuticular proboscis walls, which are functionally related to feeding performance in species possessing an extremely long proboscis. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 291–304.     

Form,function and evolution of the mouthparts of blood-feeding Arthropoda

This review compares the mouthparts and their modes of operation in blood-feeding Arthropoda which have medical relevance to humans. All possess piercing blood-sucking proboscides which exhibit thin stylet-shaped structures to puncture the host's skin. The tips of the piercing structures are serrated to provide anchorage. Usually, the piercing organs are enveloped by a soft sheath-like part which is not inserted. The piercing process includes either back and forth movements of the piercing structures, or sideways cutting motions, or the apex of the proboscis bears teeth-like structures which execute drilling movements. Most piercing-proboscides have a food-canal which is separate from a salivary canal. The food-canal is functionally connected to a suction pump in the head that transports blood into the alimentary tract. The salivary canal conducts saliva to the tip of the proboscis, from where it is discharged into the host. Piercing blood-sucking proboscides evolved either from (1) generalized biting-chewing mouthparts, (2) from piercing mouthparts of predators, or plant sap or seed feeders, (3) from lapping or sponging mouthparts. Representatives of one taxon of Acari liquefy skin tissue by enzymatic action. During feeding, many blood-feeding arthropods inadvertently transmit pathogens, which mostly are transported through the discharged saliva into the host.     

Ultrastructure of the mouthparts of adult sweetpotato whitefly,Bemisia tabaci Gennadius (Homoptera: Aleyrodidae)

The fine structure of the mouthparts of the whitefly, Bemisia tabaci Gennadius (Homoptera: Aleyrodidae), was examined by scanning and transmission electron microscopy. Adult whitefly mouthparts are similar to those of other homopterans, especially aphids, being composed of the labrum, the labium, and the stylets. The stylet bundle is the feeding organ of the whitefly and is composed of 2 mandibular stylets and 2 maxillary stylets. Mandibular stylets, which are located on the outer aspect of the stylet bundle, each contain 2 dendrites. The tips of the mandibular stylets are curved inward, and there are barb-like ridges on the lateral aspects, which probably function in piercing and cutting plant tissues and in anchoring the stylets in the tissues. The maxillary stylets are not innervated and are interlocked to form 2 separate compartments, the food canal and salivary canal. At the distal end of the interlocked maxillary stylets, there is a small depression, which may allow for mixing of the salivary canal and food canal components. Movement of the B. tabaci stylets during feeding is discussed in comparison with other homopterans.     

Morphology of the mouthparts of the spittlebug Philagra albinotata Uhler (Hemiptera: Cercopoidea: Aphrophoridae)

Mouthparts associated with feeding behavior and feeding habits are important sensory and feeding structures in insects. To obtain a better understanding of feeding in Cercopoidea, the morphology of mouthparts of the spittlebug, Philagra albinotata Uhler was examined using scanning electron microscopy. The mouthparts of P. albinotata are of the typical piercing–sucking type found in Hemiptera, comprising a cone-shaped labrum, a tube-like, three-segmented labium with a deep groove on the anterior side, and a stylet fascicle consisting of two mandibular and two maxillary stylets. The mandibles consist of a dorsal smooth region and a ventral serrate region near the apical half of the external convex region, and bear five nodules or teeth on the dorsal external convex region on the distal extremity; these are regarded as unique features that distinguish spittlebugs from other groups of Hemiptera. The externally smooth maxillary stylets, interlocked to form a larger food canal and a smaller salivary canal, are asymmetrical only in the internal position of longitudinal carinae and grooves. One dendritic canal is found in each maxilla and one in each mandible. Two types of sensilla trichodea, three types of sensilla basiconica and groups of multi-peg structures occur in different locations on the labium, specifically the labial tip with two lateral lobes divided into anterior sensory fields with ten small peg sensilla arranged in a 5 + 4 + 1 pattern and one big peg sensillum, and posterior sensory fields with four sensilla trichodea. Compared with those of previously studied Auchenorrhyncha, the mouthparts of P. albinotata may be distinguished by the shape of the mandibles, the multi-peg structures and a tooth between the salivary canal and the food canal on the extreme end of the stylets. The mouthpart morphology is illustrated using scanning electron micrographs, and the taxonomic and putative functional significance of the different structures is briefly discussed.     

A longstanding entomological problem finally solved? Head morphology of Nannochorista (Mecoptera,Insecta) and possible phylogenetic implications

External and internal head structures of Nannochorista species were examined and described in detail. The characters are discussed with regard to their functional and phylogenetic implications. The structure of the mouthparts indicates that adults of Nannochorista feed on fluids. The loss of the mandibular muscles and the precerebral pharyngeal dilators are presumptive autapomorphies of the genus. A possible clade comprising Nannomecoptera, Siphonaptera and Diptera is supported by the presence of a labral food channel, the absence of the galea, a sheath for the paired mouthparts formed by the labium, very strongly developed labial palp muscles and cibarial dilators, and the presence of a well‐defined postcerebral pharyngeal pumping chamber. Closer affinities of Nannomecoptera with Diptera are suggested by the presence of a unique sensorial groove on the third maxillary palpomere. Further potential synapomorphies are the presence of a frontal apodeme and a primarily lamelliform mandible without teeth. The presence of a salivary channel on the laciniae and a subdivided labrum are shared derived features of Nannochorista and Siphonaptera. A derived condition present in Mecoptera including Boreidae but excluding Nannochoristidae is the secretion with a strongly developed intrinsic muscle of the salivary duct. The loss of the lateral labral retractor, the cranial muscle of the cardo, and of two of the three premental retractors, and the absence of transverse epipharyngeal muscles are potential autapomorphies of Antliophora. The formation of a maxillolabial complex is a possible synapomorphy of Hymenoptera and Mecopterida.     

Development of the mouthparts in embryos of Haplothrips verbasci (Osborn) (Insecta,Thysanoptera, Phlaeothripidae)

The asymmetric “punch and suck” mouthparts of larval Haplothrips verbasci develop from paired appendages in the late, post-anatrepsis embryo similar to those of other insects. Later, the labrum flexes ventrally over the stomodaeum, the right mandibular appendage degenerates, the maxillary appendages divide into inner (lacinial) and outer (stipital) lobes, and the hypopharynx arises from the venters of the mandibular and maxillary segments. All cephalic segments consolidate anteriorly prior to katatrepsis, their appendages flex ventrally, and the labial appendages fuse medially to form the labium and the primordia of the salivary glands and valve. The left mandible and the lacinial lobes of the maxillae invaginate into the head during and after katatrepsis to form the mandibular and maxillary stylet-secreting organs and these later deposit the cuticle of their respective stylets. Cuticle of the mandibular lever is deposited by labral cells at the apex of the mandibular sheath during and after hatching. That of each maxillary lever is secreted simultaneously into the lumen of a ventrally-directed diverticulum developing from stipital cells at the apex of each maxillary sheath. Shortly after katatrepsis, the maxillary and labial palpi originate respectively from cells in the outer wall of each stipital lobe and at the apex of the labium. Muscles of the mouthparts arise after katatrepsis from cephalic mesoderm and are fully-differentiated before cuticle of the mandibular and maxillary levers has been deposited. Gnathal morphogenesis in embryos of H. verbasci resembles that occurring in bug embryos and provides additional evidence that Thysanoptera and Hemiptera evolved from a common psocopteroid stem species having small, paired, biting and chewing mandibles and well developed lacinial stylets.     

Comparative morphology and ultrastructure of the mouthparts in unfed larvae of <Emphasis Type="Italic">Platytrombidium fasciatum</Emphasis> and <Emphasis Type="Italic">Camerotrombidium pexatum</Emphasis> (Acariformes: Microtrombidiidae)

The mouthparts of unfed larvae of Platytrombidium fasciatum (C. L. Koch, 1836) and Camerotrombidium pexatum (C. L. Koch, 1837) (Acariformes: Microtrombidiidae) were studied using both light optical (whole-mounted specimens, toluidine blue stained semi-thin sections) and electron microscope (TEM, SEM) methods. The mouth apparatus incorporated within the gnathosoma occupies an axial position and is covered from above by the arched dorsal shield, or scutum. The chelicerae are comparatively long and separated, and the lateral lips form a permanent apomorphic sucker provided with an internal cuticular sclerite. The pharynx is extremely wide and totally fused with the bottom of the infracapitulum. The pharyngeal dilators originate on the posterior portions of the cervix (epistome) and on the capitular apodemes and run nearly parallel to the cervix to the dorsal pharyngeal wall. Comparatively short sigmoid pieces serve as origin of the muscles—cheliceral levators inserting on the posterior wall of the basal cheliceral segments. There are two sets of the extrinsic gnathosomal muscles originating on the posterior portion of the scutum: retractors of chelicerae inserting on the posterior portions of the basal cheliceral segments, and retractors of the gnathosoma inserting on the very posterior parts of the capitular apodemes. The labrum and the cervix delimit the pharynx and the subcheliceral space. The labrum and the cervix for the most part are weakly sclerotized cuticular plates and do not have own muscles. The larval mouth apparatus, in comparison with that of adult microtrombidiid mites, is simply organized and more specialized for ingestion of large masses of liquid food.     

Water permeability of isolated cuticular membranes: The effect of cuticular waxes on diffusion of water

Summary The water permeability of astomatous cuticular membranes isolated from Citrus aurantium L. leaves, pear (Pyrus communis L.) leaves and onion (Allium cepa L.) bulb scales was determined before and after extraction of cuticular waxes with lipid solvents. In pear, the permeability coefficients for diffusion of tritiated water across cuticular membranes (CM) prior to extraction [P _d(CM)] decreased by a factor of four during leaf expansion. In all three species investigated P _d(CM) values of cuticular membranes from fully expanded leaves varied between 1 to 2×10^-7 cm^-3 s^-1·P _d(CM) values were not affected by pH. Extraction of cuticular waxes from the membranes increased their water permeability by a factor of 300 to 500. Permeability coefficients for diffusion of THO across the cutin matrix (MX) after extraction [P _d(MX)] increased with increasing pH. P _dvalues were not inversely proportional to the thickness of cuticular membranes. By treating the cutin matrix and cuticular waxes as two resistances acting in series it was shown that the water permeability of cuticles is completely determined by the waxes. The lack of the P _d(CM) values to respond to pH appeared to be due to structural effects of waxes in the cutin matrix. Cuticular membranes from the submerse leaves of the aquatic plant Potamogeton lucens L. were three orders of magnitude more permeable to water than the cuticular membranes of the terrestrial species investigated.Abbreviations CM cuticular membrane - MX cutin matrix - WAX waxes This study was supported by a grant from the Deutsche Forschungsgemeinschaft.     

Fine structure and sensory apparatus of the mouthparts of the pear psyllid,Cacopsylla chinensis (Yang et Li) (Hemiptera: Psyllidae)

The pear psyllid, Cacopsylla chinensis (Yang et Li) (Hemiptera: Psyllidae), is one of the most significant economic pests of pear in China, causing direct damage through feeding by the highly specialized piercing–sucking mouthparts. The ultrastructural morphology and sensory apparatus of the mouthparts of the adult were examined using scanning and transmission electron microscopy. The piercing–sucking mouthparts of C. chinensis are composed of a three-segmented labium with a deep groove in the anterior side, a stylet fascicle consisting of two mandibular and two maxillary stylets, and a pyramid-shaped labrum. Proximal to the labium, the stylet fascicle forms a large loop within a membranous crumena. Mandibles, with more than ten teeth on the external convex region, can be seen on the distal extremity. Smooth maxillary stylets are interlocked to form a larger food canal and a smaller salivary canal. One dendritic canal housing 2 dendrites is also found in each mandible. Two types of sensilla trichodea, four types of sensilla basiconica, single as well as groups of sensilla campaniformia, and oval flattened sensilla occur in different locations on the labium, whereas a kind of sensilla basiconica is at the junction of the labrum and anteclypeus. Sensilla trichodea and sensilla campaniformia, always present with denticles, are present on the middle labial segment. Three types of sensilla basiconica, two types of sensilla trichodea and two oval flattened sensilla are located on the distal labial segment. The mouthpart morphology and abundance of sensilla located on the labium in C. chinensis are illustrated, along with a brief discussion of their taxonomic and putative functional significance.     

Structural mouthpart interaction evolved already in the earliest lineages of insects

In butterflies, bees, flies and true bugs specific mouthparts are in close contact or even fused to enable piercing, sucking or sponging of particular food sources. The common phenomenon behind these mouthpart types is a complex composed of several consecutive mouthparts which structurally interact during food uptake. The single mouthparts are thus only functional in conjunction with other adjacent mouthparts, which is fundamentally different to biting–chewing. It is, however, unclear when structural mouthpart interaction (SMI) evolved since this principle obviously occurred multiple times independently in several extant and extinct winged insect groups. Here, we report a new type of SMI in two of the earliest wingless hexapod lineages—Diplura and Collembola. We found that the mandible and maxilla interact with each other via an articulatory stud at the dorsal side of the maxillary stipes, and they are furthermore supported by structures of the hypopharynx and head capsule. These interactions are crucial stabilizing elements during food uptake. The presence of SMI in these ancestrally wingless insects, and its absence in those crustacean groups probably ancestral to insects, indicates that SMI is a groundplan apomorphy of insects. Our results thus contradict the currently established view of insect mouthpart evolution that biting–chewing mouthparts without any form of SMI are the ancestral configuration. Furthermore, SMIs occur in the earliest insects in a high anatomical variety. SMIs in stemgroup representatives of insects may have triggered efficient exploitation and fast adaptation to new terrestrial food sources much earlier than previously supposed.     

Composite,haustellate mouthparts in netwinged beetle and firefly larvae (Coleoptera,Cantharoidea: Lycidae,Lampyridae)

During lycid embryogenesis, labral and mandibular anlagen develop separately. Each anterolateral corner of the labrum elongates into a stylet, while the whole of each mandible involutes into a flute that is open to the lateral aspects. The stylets and flutes interlock in such a way as to leave canals, fashioning left and right haustellate apparatuses. During lampyrid embryogenesis, only one pair of anlagen forms instead of two. The pair matures into sharp, arcuate appendages that appear to be typical mandibles, but nevertheless a canal forms internally. The canal is not formed by coadaptation of two appendages; instead, cells within the pair create the canal autonomously. Indications are that the canal is homologous between these two families. It is suggested that in lampyrids, labral and mandibular cell fields develop together in the same anlage but behave according to their own respective programs, forming the canal with morphogenetic movements that are comparable to those of lycids. © 1994 Wiley-Liss, Inc.     

Ultrastructure of the black currant gall mite, Cecidophyopsis ribis (Acari: Eriophyidae), the vector of the agent of reversion disease

Electron microscopy of ultrathin serial sections was used to determine the structure and anatomy of the eriophyid gall mite, Cecidophyopsis ribis, the vector of the agent of black currant reversion disease. The composite picture derived from these studies has determined the location of the food canal, and major internal organs of the mite. Detailed ultrastructural studies on the anterior of suitably orientated mites has also provided detailed information on the geometry and complex structure of three sets of stylets in the feeding apparatus. No evidence was found of structures resembling virus-like particles or of other described plant pathogens in the feeding apparatus and food canal of mites obtained from black currant plants affected with reversion disease. However, little or no food was apparently present in the food canal of most mites examined. This is the first detailed report of the anatomy and the ultrastructure of the mouthparts of this important plant pest and vector.     

Phase behaviour and crystallinity of plant cuticular waxes studied by Fourier transform infrared spectroscopy

The phase behaviour of cuticular waxes from leaves of Hedera helix L. and Juglans regia L. was studied by Fourier transform infrared spectroscopy. For this purpose reconstituted waxes, isolated cuticular membranes, dewaxed polymer matrix membranes and whole leaves were studied in the horizontal attenuated total reflection and transmission modes. Melting curves of cuticular waxes were derived from temperature-dependent changes in the absorption maximum of the symmetric stretching mode of CH₂ groups (ν_s, at approx. 2856–2848 cm⁻¹). With increasing temperature absorption band doublets due to CH₂ scissoring (δ_sciss) and rocking (δ_rock) movements (at approx. 1473–1471 and 730–720 cm⁻¹, respectively) indicative of an orthorhombic arrangement of alkyl chains merged into a single peak. The area ratio of the peaks at approx. 720 and 730 cm⁻¹ was used as a measure for aliphatic crystallinity of plant cuticular waxes at a given temperature. The investigations of reconstituted cuticular waxes and those still embedded in isolated cuticles or in situ on the leaf produced comparable results. The findings are discussed in terms of the properties of the cuticular transport barrier. Received: 21 March 1997 / Accepted: 25 April 1997     

Periclinal penetration of potassium permanganate into mature cuticular membranes ofAgave andClivia leaves: new implications for plant cuticle development

Staining cuticular membranes ofAgave americana andClivia miniata en bloc with potassium permanganate results in a strong contrast in the interior cuticular layer while the exterior part remains unstained. This is not caused by a selective chemical reaction with the interior part but by the unidirectional penetration of the reagent from the interior side, the outside being protected by the cuticle proper. In transverse cryosections of the cuticular membrane, permanganate penetrates nearly as easily into the exterior cuticular layer as into the interior one giving the same contrast. However, compared with the periclinal penetration into the cuticle proper this penetration is accelerated five-to tenfold by the polysaccharide network within the cuticular layer which serves as a distribution-channel system. Periclinal penetration into the cuticle proper occurs independently in each cutin penetration unit included between two obvious lucent lamellae and further divided into subunits.     

Ultrastructure of an exocrine dermal gland in the gills of the grass shrimp,Palaemonetes pugio: Occurrence of transitory ciliary axonemes associated with the sloughing and reformation of the ductule

Exocrine dermal glands, comparable to the class 3 glandular units of insects, are found in the gills of the grass shrimp, Palaemonetes pugio. The dermal glands are composed of three cells: secretory cell, hillock cell and canal cell. Originating as a complex invagination of the apical cytoplasm of the granular secretory cell, a duct ascends through the hillock and canal cells to the cuticular surface. The duct is divisible into four regions: the secretory apparatus in the granular secretory cell, the locular complex, the hillock region within the hillock cell and the canal within the canal cell. A tubular ductule is contained within the latter two regions. As the ductule ascends to the cuticular surface, its constitution gradually changes from one of a fibrous material to one which possesses layers of epicuticle. During the proecdysial period, the ductule is extruded into the ecdysial space and this is followed by the secretion of a new ductule. Temporary ciliary structures, located near the secretory apparatus of the secretory cell, are associated with the extrusion and reformation of the ductule. Characterized only by a basal body and rootlets throughout most of the intermolt cycle, the ciliary organelles give rise to temporary axonemic processes which ascend through the ductule toward the ecdysial space at the onset of proecdysis. Subsequently, the old ductule is sloughed off and a new ductule is reformed around the ciliary axonemes. Following this reformation, the ciliary axonemes degenerate. The function of cytoplasmic processes, derived from the apical cytoplasm of the secretory cell, is also discussed.     

Water permeability of plant cuticular membranes: the effects of humidity and temperature on the permeability of non-isolated cuticles of onion bulb scales

Abstract. Water permeability of cuticular membranes (CM) from the inner bulb scales of Allium cepa has been investigated. CM have a thickness ranging from 0.6 to 1.3 μm. They are composed of a thin (120–200 nm) lamellated cuticle proper and a thicker (300–900 nm) cuticular layer. Permeability coefficients for diffusion of water across these thin membranes are very low (4 × lO⁻¹⁰ms⁻¹⁰). There was no difference in permeability of CM from successive scales of the same onion. Extraction of soluble cuticular lipids (SCL) with chloroform increased permeability by a factor of 1350 to 2050. Preliminary data indicate that only 1 μg cm⁻¹⁰ of SCL are removed by this treatment, hydrocarbons being the main (75%) consistuent. Permeability coefficients of cuticular transpiration were little affected by relative humidity, showing that transport is limited by a hydrophobic barrier that lacks dipoles. However, following extraction, permeability of the membranes depended strongly on humidity due to the presence of polar functional groups in the polymer matrix. Soluble cuticular lipids undergo a phase transition around 47°C. Temperatures higher than that irreversibly increased water permeability.