Chemosensory control of pollen ingestion in the hoverfly Eristalis tenax by labellar taste hairs

The labellar gustatory system of the dronefly Eristalis tenax L. (Syrphidae; Diptera) that enables the fly to discriminate between pollen and nectar is investigated, and the triggering of pollen ingestion is examined. In behavioural preference tests, exhaustively extracted pollen of the sunflower Helianthus annuus is consumed in smaller amounts than untreated pollen, indicating that water-soluble substances are important for acceptance. Dry pollen is preferred over moist pollen in which the grains stick together, suggesting that mechanical properties of the pollen also play a role in its sensory assessment. Electrophysiological studies of the labellar taste hairs reveal that aqueous extracts of pollen (2% w/v) stimulate the salt receptor cell, but not the sugar receptor cell. The response of the water receptor cell remains the same as to pure water (or standard electrolyte, 10 mmol · l⁻¹ KCl). Of the 20 amino acids tested, the salt cell is sensitive only to proline in a submillimolar range. Behavioural experiments support the electrophysiological findings. When KCl is applied at concentrations eliciting salt-cell spike frequencies equal to those produced by pollen extract (which is often accepted), the water receptor cell is inhibited and a pronounced rejection behaviour occurs. This rejection of concentrated salt solution in Eristalis is therefore mainly mediated by the inhibition of the water cell. Accepted: 27 November 1999     

Supravital Methylene Blue Staining of Piloneural Complexes of Common Fur Hair Follicles in the Rat

Light microscopic observations employing supravital methylene blue staining are presented for piloneural complexes of common fur hairs in the mystacial pad of the rat snout. The investigation revealed anatomical details of piloneural complexes belonging to follicles of both vellus and guard hairs. In the methylene blue stained preparations, different types of palisade-like lanceolate nerve fiber endings could be discriminated. The thicker vellus and thinner guard hairs (hair diameter: 15-25 μm) exhibited a different innervation pattern compared to the thicker guard hairs, and two subtypes of piloneural complexes could be distinguished. Both subtypes were characterized by slightly stained lanceolate endings and the absence of a circular nerve fiber plexus. One subtype, however, showed strongly stained spines originating from the lanceolate endings. A few spines of adjacent lanceolate endings appeared in contact with each other. In the second subtype, these spines were replaced by anastomoses suggesting a delicate terminal nerve fiber network. The moderately stained lanceolate endings located primarily at the follicles of thicker guard hairs (hair diameter: 30-40 μm) showed smooth outlines, but were characterized by the occurrence of an intensely stained additional circular nerve fiber plexus. The differences in the morphology of piloneural complexes associated with the follicles of common fur hairs suggest differences regarding their mechanoreceptive tasks.     

“Balloon hairs” of gipsy moth larvae (Lep., Lymantriidae): morphology and comparative chemistry

The “balloon hairs” of L₁ caterpillars of Lymantria dispar (Lep., Lymantriidae) are jointed, hollow and filled with a fluid. Detection of nicotine in the balloon hairs as well as feeding-deterrent effects of whole larvae and nicotine on ants indicate that these setae serve for defense against predatory arthropods and parasitoids but not for soaring of the larvae. Titers of nicotine and other components were determined for several developmental stages of L. dispar and compared.     

中国黄耆属糙叶组叶表皮毛状体微形态学特征

采用体视显微镜和扫描电子显微镜,对中国产黄耆属糙叶组34种植物的叶表皮毛状体的形态特征及其分布进行了观察,以探讨中国黄耆属糙叶组物种表皮毛微观形态的变异式样及其分类学意义,为糙叶组物种的分类鉴定提供依据。结果表明：除乳白花黄耆（A. galactites）仅在叶下表面被毛外,其余种类上下表皮均有毛,且毛的分布、形态、长度和臂比在不同种类间存在差异。叶表皮毛为伏贴或开展的中空管状毛,伏贴毛着生部位基部膨大,整体形态从中部向两端由粗逐渐变细,开展的毛大部分为细长的丝状或线状,光滑或具条纹状纹饰,上面分布有乳突。研究认为,叶表皮表面伏贴、短而平直、其上光滑具密集乳突、臂比值小、整体宽扁的毛是祖先特征;而叶表皮表面向上开展、长而密集、外形呈丝状或线形、其上具条纹状纹饰、乳突稀疏、臂比值大的毛是进化特征。     

ULTRASTRUCTURAL VARIATIONS IN CRYPTOMONAD FLAGELLA1

The arrangement of flagellar appendages in 19 cryptomonad species was examined and four new flagellar types are described. The first new type has a single row of mastigonemes on both flagella and hairs on the side opposite the mastigonemes. The second type, which is common, has unilateral rows of mastigonemes on both flagella, but no hairs. A third type has an acronematic short flagellum and a single row of mastigonemes on the long flagellum. A fourth type lacks mastigonemes but has a unilateral row of curved “spikes” on the short flagellum and hairs on both flagella. These additional flagellar variations may contribute to a more natural system of classification for cryptomonads.     

The longevity and activity of the primary root of maize

The longevity of the main root cylinder and the laterals of the primary root of maize plants was determined under controlled greenhouse conditions by means of nuclear staining with acridine orange. The cortex of the main root was found to be alive for the whole life-span of the plant, whereas the life-span of the root hairs was only 2 to 3 days as evidenced by electronmicroscopical examination of cell integrity. The onset of senescence of laterals was observed at the older part of the main root at the 6-leaf stage of the plant. Senescence of 1st and 2nd order laterals commenced near the root tip a few days after their protrusion and advanced towards the basal region of the root. In any root segment death of the cortex cells preceeded that of the stele. At the late grain filling stage all laterals along the main root exhibited advanced senescence, but stainable nuclei were seen in the root tissues of the basal part of 1^st order laterals (both cortex and stele) as well as of the 2^nd order laterals which emerged from that root segment. The pattern of the dying of the root tissue is discussed with regard to the P-nutrition of the shoot system by the primary root.     

Taxonomical significance of the leaf indument inDryopteris (Pteridophyta): I. Some North American,Macaronesian and European taxa

The leaf indument of a number of North American, Macaronesian and EuropeanDryopteris taxa is described. Trichome characters provide very useful taxonomical data for the study of species complexes and for tracing relationships among geographically isolated or separated taxa. The new combination,D. expansa var.alpina, is made. The present study sustains best theWagner D. semicristata relationship scheme.     

Die Feinstruktur der tarsalen Schmeckhaare der Fliege Phormia terraenovae Rob.-Desv.

Zusammenfassung Die Schmeckhaare der Fliege Phormia terraenovae enthalten fünf Rezeptorzellen (vier Kontaktchemo- und eine Mechanorezeptorzelle), die von zwei Hüllzellen unter Aussparung von Lymphräumen (Vakuole) umgeben sind. Die Rezeptorzellen gliedern sich in Axon, Zellkörper und Dendrit, der aus Innenglied, Übergangsabschnitt und Außenglied besteht. Der Übergangsabschnitt hat die 9+0-Struktur der modifizierten Cilien mit zwei Basalkörpern. Im Plasma der Außenglieder sind nur Mikrotubuli zu erkennen. Die Außenglieder der Kontaktchemorezeptoren ziehen durch die röhrenförmige Dendritenscheide und den Kanal I des Haarschafts bis zu einem Porus in der Haarspitze, durch den sie mit den Schmeckstoffen in Kontakt kommen (Ort der Primärprozesse). Das Außenglied der Mechanorezeptorzelle enthält einen tubulären Körper und setzt an der Haarbasis an. Die Hüllzelle II (tormogene Zelle) bildet zum großen Sensillenlymphraum hin ein stark gefaltetes Membransystem aus. Der Feinbau wird in Beziehung zur Funktion der Schmeckhaare gesetzt.

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The fine structure of the tarsal taste hairs of the blowfly, Phormia terraenovae Rob.-Desv.

Summary The tarsal taste hairs of the blowfly contain five receptor cells: four contact chemoreceptors and one mechanoreceptor. These cells are surrounded concentrically by two sheath cells with fluid-filled spaces (vacuoles) between them. The receptor cell parts are the axon, the cell body, and the dendrite. The latter has an inner segment, a transitional region, and an outer segment. The transitional region shows the 9+0 configuration of a modified cilium with two basal bodies. In the outer segment only microtubules are found. The outer segments of contact chemoreceptors pass through the tube-like dendrite sheath, then through canal I of the hair shaft, to reach the pore at the tip of the hair. The outer segment of the mechanoreceptor contains a tubular body and terminates at the hair base. The sheath cell II (tormogene cell) forms a folded membrane system toward the main liquor space. The fine structure of the tarsal taste hairs is discussed in relation to their function.

Den Herren Dr. W. Pflumm, Prof. Dr. U. Thurm, Prof. Dr. E. Schnepf und Dr. K. E. Kaissling sei für anregende Diskussionen und der Deutschen Forschungsgemeinschaft für eine Sachbeihilfe gedankt. Frau R. Föhr danken wir für ausgezeichnete technische Mitarbeit.