Kusum Singh

Bio: Kusum Singh is an academic researcher from Tata Institute of Fundamental Research. The author has contributed to research in topics: Sensillum & Aphididae. The author has an hindex of 7, co-authored 13 publications receiving 319 citations.

Fine structure of the sensory organs of Drosophila melanogaster Meigen larva (Diptera : Drosophilidae)

Abstract: Fine structure of the prominent external and internal sensory organs of Drosophila melaogaster Meigan (Diptera : Drosophilidae) larva was determined by transmission electron microscopy (TEM). The external sensory organs, namely, antennal, maxillary, ventral and labial organs, dorsal pits, sensory cones on the 8th and 9th abdominal segments, and the sensory hairs on the body of the larva, were studied. A new knob in pit (KIP) sensillum innervated by 3 dendrites was found on the dorsolateral surface on either side. Four tufts of hairs at the posterior end of each great lateral tracheal trunk were found to be sensory with a dendrite at the base of each tuft. Internally in the pharynx of the larva, 3 groups of symmetrically located sensory organs, namely, the anteroventral, dorsal, and posteroventral groups were found. In all they contain 10 pairs of sensilla. Amongst them, 2 pairs of sensilla were found to be of the compound type; one having 9 dendrites arranged in 3 groups of 4, 3 and 2; while the other had 6 dendrites grouped as 2 and 4. In addition, 2 groups of sensilla were found on the internal dorsal fold on either side. Similarities were observed in the dendritic organisation of sensilla in the internal mouthparts of the Drosophila larva and the adult. Unlike nerves of the adult, the larval nerves connected with the dorsal and maxillary organs have a significantly thick layer of glial cells ensheathing the bundle of axons.

Fine structure and primary sensory projections of sensilla located in the sacculus of the antenna of Drosophila melanogaster.

Abstract: Sensilla lining the inner walls of the sacculus on the third antennal segment of Drosophila melanogaster were studied by light and transmission electron microscopy. The sacculus consists of three chambers: I, II and III. Inside each chamber morphologically distinct groups of sensilla having inflexible sockets were observed. Chamber I contains no-pore sensilla basiconica (np-SB). The lumen of all np-SB are innervated by two neurons, both resembling hygroreceptors. However, a few np-SB contain one additional neuron, presumed to be thermoreceptive. Chamber II houses no-pore sensilla coeloconica (np-SC). All np-SC are innervated by three neurons. The outer dendritic segments of two of these neurons fit tightly to the wall of the lumen and resemble hygroreceptor neurons. A third, more electron-dense sensory neuron, terminates at the base of the sensillum and resembles a thermoreceptor cell. Chamber III of the sacculus is divided into ventral and dorsal compartments, each housing morphologically distinct grooved sensilla (GS). The ventral compartment contains thick GS1, and the dorsal compartment has slender sensilla GS2. Ultrastructurally, both GS1 and GS2 are doublewalled sensilla with a longitudinal slit-channel system and are innervated by two neurons. The dendritic outer segment of one ofthe two neurons innervates the lumen of the GS and branches. On morphological criteria, we infer this neuron to be olfactory. The other sensory neuron is probably thermoreceptive. Thus, the sacculus in Drosophila has sensilla that are predominantly involved in hygroreception, thermoreception, and olfaction. We have traced the sensory projections of the neurons innervating the sacculus sensilla of chamber III using cobaltous lysine or ethanolic cobalt (II) chloride. The fibres project to the antennal lobes, and at least four glomeruli (VM3, DA3 and DL2-3) are projection areas of sensory neurons from these sensilla. glomerulus DL2 is a common target for the afferent fibres of the surface sensilla coeloconica and GS, whereas the VM3, DA3 and DL3 glomeruli receive sensory fibres only from the GS.

Ultrastructure of the femoral chordotonal organs and their novel synaptic organization in the legs of Drosophila melanogaster Meigen (Diptera : Drosophilidae)

Abstract: The chordotonal or scolopophorous organs located in the femoral segment of all the legs of both male and female Drosophila melanogaster (Diptera : Drosophilidae) were examined by light and transmission electron microscopes. The femoral chordotonal organs (FCO) are arranged in 3 groups: one large group consists of about 32 aligned scolopes whose distal ends extend and terminate at the distal epicuticular surface of the femur; the other 2 central groups together contain about 42 scattered scolopes, and distally they terminate into the membranes connecting the muscles of the femur. No sexual dimorphism is evident either in the numbers of scolopidial groups or the total number of scolopidia in both sexes. Each scolopidium is innervated by 2 neurons of which one is less electron-dense than the other. The dendrites of these neurons bear sensory cilia. The fine structure of these chordotonal sensilla suggests that they probably respond to stretch or flexion. Proximally in the femur, the axons from FCO form a novel glomerular organization. These axons show lateral extensions and form different morphological types of synapses among themselves. From the presence of a large number of putative chemical synapses in the legs, it is evident that some degree of information processing is taking place in D. melanogaster at the periphery before being relayed to the central nervous system.

Sensory organs on the body parts of the bed-bug Cimex hemipterus fabricius (Hemiptera : Cimicidae) and the anatomy of its central nervous system

Abstract: Anatomy of the sensory organs on the prominent body parts of the adult bed-bug Cimex hemipterus (Hemiptera: Cimicidae) and its central nervous system (CNS) was studied by light, transmission, or scanning electron microscopy. The distal tips of antenna and rostrum were found to have rich complements of sensilla. The antenna has both olfactory and gustatory sensilla. Olfactory sensilla project to the antennal lobe organized in the form of glomeruli, while the 2nd component, presumably from gustatory sensilla, projects to the suboesophageal ganglion. The ultrastructure of the sensory pegs on the rostrum of C. hemipterus does not resemble the chemosensilla of adult insects; rather they resemble the larval sensilla of Drosophila melanogaster in the maxillary organ. Earlier we believed this to be a gustatory organ. A few similar sensilla also occur on the antenna, indicating its multimodal role. Amongst the 3 types of sensory hairs located on legs, there are only a few gustatory hairs (7–10 hairs) on the tibia. The pointed and serrate mechanosensory hair types occur in abundance; the serrate type are prominently present on the lateral surface of the legs. On other parts of the body such as the thorax or abdomen, serrate hairs are most abundant. Both the distal segment of antenna and rostrum are invested by 2 nerves, where the axon counts of the 2 antennal nerves are 380 and 425, while each rostral nerve on average has 205 axons. Abundant clusters of microtubules were found in the brain, thoracio-abdominal ganglia, leg-nerves, and the space between muscles and cuticle. These conspicuous microtubule-clusters occur in interaxonal space, mainly glial cells, in the nervous system. In addition, the glial cells have osmiophilic junctions amongst themselves. A novel “hinge and joint” system, which controls the cross-section of the food canal and the salivary duct in an inversely related manner, was found in the rostrum of the bed-bug.

Sensilla on the maxillary and labial palps of the cockroach Supella longipalpa fabricius (Dictyoptera : Blattellidae)

Abstract: Sensory structures on the maxillary and labial palps of Supella longipalpa (Dictyoptera : Blattellidae) were examined by light, scanning, and transmission electron microscopy. Maximum variety of sensilla, including olfactory, gustatory, and mechanosensory, were found on the most distal segments of maxillary as well as labial palps. The maxillary palp has a long micro-furrow near the ventral edge of the medial surface of the fifth segment, which has a high population density of 73,700 sensilla/sq. mm 2 . These sanilla are mostly 3–5-μm-high, 1.5–1.8-μm-thick pegs with grooves along the hair-shaft and a slit near the distal tip. The slit and the typical arched fenestration at the tip, may allow the dendrites to sample the external environment. This groove-and-slit sensillum is a new sensillum described for the first time in insects, and we designate it as GAS sensillum. Based on its morphology and also its sensory projections leading to the antennal lobes of the brain, as revealed by cobalt(II) uptake, the GAS sensillum appears to be olfactory. The sensillary complement on both palps is qualitatively similar, except for the presence of GAS sensilla on the maxillary palp. However, the quantitative estimates of the number of sensilla on both maxillary and labial palps of females as well as males, show that both palps have sexual dimorphism. S. longipalpa males have more chemosensilla on the maxillary palp and more taste sensilla on the labial palp than females. Uptake of cobalt(II) by sensilla on the distal region of the maxillary palps shows an olfactory component, projecting to the glomeruli of the antennal lobe, whereas the gustatory and mechanosensory projections of sensilla on the maxillary as well as labial palps, are mainly confined to the suboesophageal ganglion.

The Organization of the Chemosensory System in Drosophila Melanogaster: A Review

Abstract: This review surveys the organization of the olfactory and gustatory systems in the imago and in the larva of Drosophila melanogaster, both at the sensory and the central level. Olfactory epithelia of the adult are located primarily on the third antennal segment (funiculus) and on the maxillary palps. About 200 basiconic (BS), 150 trichoid (TS) and 60 coeloconic sensilla (CS) cover the surface of the funiculus, and an additional 60 BS are located on the maxillary palps. Males possess about 30% more TS but 20% fewer BS than females. All these sensilla are multineuronal; they may be purely olfactory or multimodal with an olfactory component. Antennal and maxillary afferents converge onto approximately 35 glomeruli within the antennal lobe. These projections obey precise rules: individual fibers are glomerulus-specific, and different types of sensilla are associated with particular subsets of glomeruli. Possible functions of antennal glomeruli are discussed. In contrast to olfactory sensilla, gustatory sensilla of the imago are located at many sites, including the labellum, the pharynx, the legs, the wing margin and the female genitalia. Each of these sensory sites has its own central target. Taste sensilla are usually composed of one mechano-and three chemosensory neurons. Individual chemosensory neurons within a sensillum respond to distinct subsets of molecules and project into different central target regions. The chemosensory system of the larva is much simpler and consists essentially of three major sensillar complexes on the cephalic lobe, the dorsal, terminal and ventral organs, and a series of pharyngeal sensilla.

Physiological Diversity in Insects: Ecological and Evolutionary Contexts.

Abstract: Publisher Summary This chapter discusses the modern ecological and evolutionary contexts of the evolutionary physiology in insects and provides a survey of sources of environmental variability and their effects on insect populations. The chapter explores environmental variation and the various ways in which it may be quantified. Some environmental variables are relatively simple and straightforward, both to measure and to control, whereas others pose substantially greater problems from both perspectives. Even variables that are seemingly easy to measure might act in ways that are difficult to identify. The chapter examines insect responses to the thermal environment over a variety of spatial and temporal scales, focusing on recent developments in the field. The importance of water availability for insect survival and the determination of distribution and abundance patterns have been widely demonstrated. The chapter considers the question of what lessons insect evolutionary physiologists might have to offer ecology and conservation biology. In particular, how evolutionary physiology can offer ecologists a set of useful general rules in some cases and can unveil the nature of local contingency in others.

Complementary Function and Integrated Wiring of the Evolutionarily Distinct Drosophila Olfactory Subsystems

Abstract: To sense myriad environmental odors, animals have evolved multiple, large families of divergent olfactory receptors. How and why distinct receptor repertoires and their associated circuits are functionally and anatomically integrated is essentially unknown. We have addressed these questions through comprehensive comparative analysis of the Drosophila olfactory subsystems that express the ionotropic receptors (IRs) and odorant receptors (ORs). We identify ligands for most IR neuron classes, revealing their specificity for select amines and acids, which complements the broader tuning of ORs for esters and alcohols. IR and OR sensory neurons exhibit glomerular convergence in segregated, although interconnected, zones of the primary olfactory center, but these circuits are extensively interdigitated in higher brain regions. Consistently, behavioral responses to odors arise from an interplay between IR- and OR-dependent pathways. We integrate knowledge on the different phylogenetic and developmental properties of these receptors and circuits to propose models for the functional contributions and evolution of these distinct olfactory subsystems.