Comparison of the egg-laying behaviour and electrophysiological responses of Delia radicum and Delia floralis to cabbage leaf compounds

Abstract.  The behaviour and the sensitivity of adult cabbage root fly, Delia radicum and turnip root fly, Delia floralis are compared with host-plant extracts and isolated crucifer compounds previously identified as oviposition stimulants for D. radicum . The oviposition behaviour of both species is similar; 7–10-day-old females are stimulated to lay eggs by the methanol extract of cauliflower leaves that contains thia-triaza-fluorenes (CIF) as well as glucosinolates. The glucosinolate fraction is mainly composed of glucobrassicin, which alone stimulate both fly species to lay eggs. The C₅ and D_3,4 sensilla on the prothoracic tarsae of newly-emerged D. radicum contain neurones sensitive to the glucosinolate fractions tested and to glucobrassicin, whereas the CIF specifically stimulate a neurone in the C₅ sensillum. By contrast, newly-emerged D. floralis respond less to glucosinolates, especially to glucobrassicin, and have sensitive neurones to CIF in other sensilla than D. radicum . Recordings are also made from the longest sensilla present on the labellum because they are apparently sensitive to glucosinolates. By contrast to earlier investigations, no remarkable phasic-tonic responses of these neurones are seen. The two species are difficult to discriminate visually, have the same host plants, show identical host-selection behaviour, apparently respond to the same physical and chemical properties of their host-plants, but have a clearly different distribution of receptor neurones in the tarsal sensilla.     

Central afferent pathways of long hair sensilla in the ventral nerve cord of the Indian black scorpion,Heterometrus fulvipes Koch

Histological and electrophysiological studies of identified long hair sensilla (LHS) have provided information on primary afferent fibre pathways in the ventral nerve cord of the Indian black scorpion, Heterometrus fulvipes.Cobalt-filling of single LHS on the metasoma showed that sensory axons enter the respective segmental ganglion, ascend ipsilaterally through the next anterior ganglia and terminate in a 4th ganglion. In each ganglion, these plurisegmental fibres give off collateral branches that terminate in the ganglionic neuropil. Fibres entering heterolateral connectives were not found.Recordings from peripheral nerves after deflections of a hair showed single or multiple spike discharges. A single spike could be recorded from ipsilateral anterior connectives of the ventral nerve cord, indicating a through-conductance of the sensory pathways. Strong deflections of a single hair activated several ipsilateral and fewer contralateral ascending interneurons and some segmentai motor neurons. Behavioral studies demonstrate the mechanoreceptive function of the LHS.The present study provides evidence in support of the notion that sensory afferents of the postabdomen in the scorpion bring about rapid, co-ordinated intersegmental movements of the multisegmented tail of the scorpion.Abbreviations CNS central nervous system - LHS long hair sensillum - TR trichobothria     

A cryofixation study of presumptive hygroreceptors on the antennule of a terrestrial isopod

The structure of the apical sensilla on the antennule of the terrestrial isopod Porcellio scaber was examined in cryofixed and freeze substituted (CRF) and chemically fixed and dehydrated (CHF) material. CRF specimens generally showed a preservation superior to CHF material. Only in deeper regions did the tissue show damage from freezing. Each of the 13–22 sensilla contains two sensory cells. In contrast to earlier reports, it was observed that the dendritic segments of these cells are arranged in a unique, concentric manner. In CRF specimens the dendrites reach the tip of the sensilla and border upon the innermost layer of the complicated wall of the peg which is not pierced by pores. Silver-protein and lanthanum failed to penetrate the wall of the sensilla and also did not reach the dendrites via an apical pore, which therefore is regarded as a molting pore. The lymph spaces which, in CHF specimens, are observed around the dendrites and beneath the cuticle within the antennal tip are regarded as artefactual. From similarities in the dendritic structures to insect hygroreceptors and their relationship to the adjoining cuticle it can be assumed that the antennular sensilla in Porcellio are sensitive to humidity changes. Mechanoreception and chemoreception, however, cannot entirely be excluded as possible functions.     

Apically administered cytochalasin B and D decreases sensitivity of electroreceptor organs in the North-American catfish,Ictalurus nebulosus

The receptor cells of the ampullary electroreceptor organs of Ictalurus nebulosus bear microvilli on the apical membrane. Whereas microvilli in mechanoreceptive hair cells and in chemoreceptor cells have a transduction function, the function of these membrane specializations in electroreceptor cells is not fully understood. To study the role of the microvilli of the electroreceptor cells, the ampullary electroreceptor organs were apically exposed to the microfilament-disrupting agents cytochalasin B and D. Electrophysiological measurements showed that cytochalasin caused a high decrease in sensitivity and a slight decrease in spontaneous activity. Exposure to cytochalasin B resulted in a striking disorganization of the microvilli on the apical membrane of the electroreceptor cells. The most plausible explanation for the results is that treatment with cytochalasin mainly affects the actin filaments of the microvilli causing an increase of the resistance of the apical membrane. A high apical resistance results in a decrease of the voltage over the basal membrane, which in turn reduces the sensitivity. The conclusion is that intact apical microvilli are necessary for proper functioning of ampullary electroreceptor organs. Alterations in microvillar properties, like surface area and ion channel conductancy might play a considerable role in the regulation of the sensitivity.     

Toenail mercury concentration as a biomarker of methylmercury exposure

The aim of the study was to assess the value of toenail mercury as an alternative biomarker of methylmercury exposure compared with blood and hair. Blood, hair and toenail total mercury concentrations were determined simultaneously in a southern urban sea n = 35 and an eastern rural lake n = 37 group and separately in a central Finnish rural lake n = 39 group. A questionnaire based index was used for estimating frequency of exposure taking into account high vs low mercury fish. Total mercury concentration was determined by cold vapour atomic absorption spectrophotometry. The mean Fish Consumption Frequency Index varied from 4.7 to 9.9 on a scale of 1-20. The blood, hair and toenail mercury mean concentrations ranged from 2.9 to 14.6 g l-1, 0.45 to 1.57 mg kg-1 and 0.20 to 0.54 mg kg-1, respectively. In the combined southern and eastern groups n = 72 sampled simultaneously, the correlations between blood and hair mercury were r = 0.92 and that of blood and toenails r = 0.78 p 0.0001 . In the central Finnish group the correlations were more moderate. In the three groups all three biomarkers correlated highly with the fish consumption index, r = 0.43-0.76 p 0.0001 . Men consumed high mercury fish more frequently than women, 8.6 vs 6.6 n.s. . The mean mercury levels of blood and hair were two fold, but toenail mercury levels were only 30 higher in men compared with those of the women. The relative sensitivity slope of the sources decreased in the order, blood hair toenails. In conclusion, toenails, an easily accessible tissue for the estimation of methylmercury exposure, have been shown to be closely correlated with the well established samples for biomarkers, viz. blood and hair mercury.     

Behavioural evidence for hygro- and mechanoreception by ovipositor sensilla of Dacus tryoni (Diptera: Tephritidae)

ABSTRACT. Gravid female Queensland fruit flies Dacus tryoni (Froggatt) readily oviposit when the ovipositor sensilla are stimulated either by a relatively thick (≥2 mm) surface layer, or by moisture under a relatively thin (<0.5 mm) or thick surface layer. A single layer of Parafilm over dry air elicits almost no oviposition; significantly more oviposition occurs when the underside of the Parafilm is coated with a 2 mm thick layer of petroleum jelly; even more oviposition occurs when the Parafilm is floated on liquid paraffin; greatest oviposition is elicited when moist media (agar gel, water or moist air) are presented under the Parafilm. Hollowed-out domes of apple skin elicit significant oviposition only when sealed basally, to give high internal concentrations of water vapour. The previously identified groove sensilla on the tephritid ovipositor are inferred as being a source of mechanical and chemical information used by the fly in such ovipositional decisions. The ovipositor also has two other types of tactile sensilla. The three types of ovipositor sensilla of tephritids are considered to play roles analogous to those of certain labial receptors of flies with piercing mouthparts.     

Analysis of immunocytochemical staining patterns in the antennal system of Drosophila melanogaster

By immunizing mice with homogenized brains, heads, or a mixture of heads and antennae of D. melanogaster, we obtained six monoclonal antibodies (mabs) that bind to the olfactory system of Drosophila with various degrees of specificity. They can be divided into three groups with respect to their staining pattern: (1) The antibodies ca51/2, na21/2, and nb230 label both in the third (olfactory) antennal segment and in the visual ganglia. All of them bind to antennal structures that can be correlated with basiconic sensilla. The antibody ca51/2 labels sensory neurons of these sensilla. In the antenna of the lozenge ³ mutant, which lacks basiconic sensilla, no labeling is present. In Western blots ca51/2 recognizes in the antenna an antigen of 43.5 kDa, which is expressed in the antenna only in the presence of basiconic sensilla. The antibody na21/2 binds to basiconic and coeloconic sensilla, most likely to the apical part of sheath cells. In immunoblots it recognizes in the antenna two antigens of 42.2 kDa and 46.7 kDa. The latter appears to be correlated in the antenna with the presence of basiconic sensilla. (2) The staining pattern of antibody nc10 is associated with the sheath cells of basiconic and coeloconic sensilla. Moreover, nc10 binds to a subset of glomeruli in the antennal lobe. (3) The staining pattern of the antibodies VG2 and I24B5 is restricted to the antenna. I24B5 recognizes coeloconic sensilla and VG2 recognizes both coeloconic and basiconic sensilla. Staining patterns in both cases include sheath cells.     

Antenna morphology and sensilla microstructure of the male and female scarab beetle,Lepidiota mansueta Burmeister (Coleoptera: Scarabaeidae)

Studies on Lepidiota mansueta Burmeister were conducted to describe and compare the external morphology of the antenna and its sensilla of male and females. Distinct variations were observed in antennal segments between the sexes with males possessing longer scape, pedicel, flagellum and lamellar club segments. Variation was also seen in the antennal sensilla, with males possessing three different types of sensilla while the females possessed seven types of sensilla. Sensilla trichodea (TRS), sensilla placodea (PLAS) type I and sensilla placodea (PLAS) type II were common in both sexes while sensilla chaetica (CHS), sensilla auricilica (AUS) type I, sensilla auricilica (AUS) type II and sensilla auricilica (AUS) type III were found only in females.     

The source of chilopod sensory information: External structure and distribution of antennal sensilla in Scutigera coleoptrata (chilopoda,Scutigeromorpha)

The investigation of the antennae of Scutigera coleoptrata (Linnaeus, 1758) by scanning electron microscopy (SEM) revealed the presence of five types of sensilla: sensilla trichodea, beak‐like sensilla, cone‐shaped sensilla brachyconica on the terminal article, sensory cones at the antennal nodes, and the shaft organ. Alongside the presence and absence of antennal sensillar types, three unique characters were found in the Scutigeromorpha: the presence of long antennae with nodes bearing sensory cones, the presence of a bipartite shaft including the shaft organ, and the presence of beak‐like sensilla. Neuroanatomical data showed that the animals' brains are equipped with well‐developed primary olfactory and mechanosensory centers, suggesting that the antennae must be equipped with specialized sensilla to perceive chemosensory and mechanosensory cues. With the evidence provided in this article for the Scutigeromorpha, SEM data are available at last on the antennal sensilla for all five chilopod taxa, allowing a comparative discussion of antennal morphology in Chilopoda. J. Morphol., 2011. © 2011Wiley‐Liss, Inc.     

Fine structure of the male genital system of the predatory mite Rhagidia halophila (Rhagidiidae,Prostigmata, Actinotrichida)

The male genital system of the actinotrichid mite Rhagidia halophila is described and compared with other mites and arachnids. The large testes are composed of germinal and glandular parts and produce numerous small sperm cells. The glandular parts are connected via a testicular bridge. Spermiogenesis occurs in cysts containing spermatids in equal stages of development. Cysts of spermatids are embedded in huge somatic cells. The nuclei of the spermatids loose their envelope. Mature sperm cells are simple exhibiting a ring‐shaped chromatin body and lacking an acrosomal complex. They are most similar to the sperm cells of the related mite Linopodes motatorius. The spermatopositor contains the ejaculatory duct divided into a dorsal channel and a ventral channel that are connected via a narrow passage. At its distal end, the spermatopositor is divided into three eugenital lips. The function of the spermatopositor during deposition of the peculiar thread‐like spermatophores is discussed. Details of the sensilla of the spermatopositor and the progenital lips are reported. The genital papillae located on the inner side of the progenital lips exhibit characteristics of cells performing transport of ions and/or water. The results confirm the overall similarity of actinotrichid genital systems, which is profoundly different from that of anactinotrichid mites. With reference to other Arachnida it is corroborated that testes and sperm structure of Actinotrichida are most similar to that of Solifugae. However, synapomorphies between sperm cells of Rhagidia and Solifugae that could suggest a closer relationship between these two taxa as was suggested in earlier studies were not recognizable. On the contrary, the sperm cells of Rh. halophila being devoid of an acrosomal complex appeared to be more apomorphic than those of many other actinotrichid mites as well as Solifugae. J. Morphol. 276:832–859, 2015. © 2015 Wiley Periodicals, Inc.