Distribution of tachykinin-related neuropeptide in the developing central nervous system of the moth Spodoptera litura

Neuropeptides with similarities to vertebrate tachykinins, designated tachykinin-related peptides (TRPs), have been identified in several insect species. In this investigation we have utilized an antiserum raised to one of the locust TRPs, locustatachykinin-I (LomTK-I), to determine the distribution pattern of LomTK-like immunoreactive (LTKLI) neurons in the developing nervous system of the moth Spodoptera litura. A number of LTKLI neurons could be followed from the larval to the adult nervous system: a set of median neurosecretory cells (MNCs) in the brain, a pair of brain descending neurons and a few sets on neurons in the ventral nerve cord. The distribution of LTKLI neurons in the adult brain is very similar to that seen in other insect species with prominent arborizations in the central body, antennal lobes, mushroom body calyces, optic lobe neuropils and other distinct neuropil areas in the protocerebrum and tritocerebrum. A new finding is the presence of LTKLI neurosecretory cells with axon terminals in the anterior aorta and corpora cardiaca, suggesting for the first time a neurohormonal role of tachykinin-related peptide(s) in insects. During postembryonic development the number of LTKLI neurons in the ventral nerve cord decreases somewhat, whereas the number increases in the brain. Thus the functional roles of TRPs may change to some extent during development.     

Building the central complex of the grasshopper Schistocerca gregaria: temporal topology organizes the neuroarchitecture of the w,x, y,z tracts

The central complex is a brain specific structure involved in multimodal information processing and in coordinating motor behaviour. It possesses a highly organized neuroarchitecture, which is remarkably conserved across insect species. A prominent feature of this neuroarchitecture is the stereotypic projection of axons from clusters of neurons in the pars intercerebralis to the central body via the so-called w, x, y and z tracts. Despite extensive analyses of this neuroarchitecture in adults, little is known about its ontogeny in any insect. In this paper we use the expression pattern of the segment polarity gene engrailed to identify those neuroblasts belonging to the protocerebrum of the early embryonic brain of the grasshopper Schistocerca gregaria. We present a new map for this brain region in which the 95 protocerebral neuroblasts in each hemisphere are organized into seven rows, as they are in the neuromeres of the ventral nerve cord. We then identify a subset of four of these neuroblasts as being the progenitor cells for four clusters of neurons, some of whose axons we show project via discrete tracts (w, x, y, z) into the central complex. These tracts begin to form prior to 39% of embryogenesis. We show further, that the cells from one of these clusters (the Z cluster) are organized according to age, and direct axons topologically according to age into the appropriate z tract. This pattern is repeated in each of the other three clusters, thus establishing a clonally based modular system of fibre tracts consistent with the model proposed for this brain region in the adult.     

Crustacean cardioactive peptide-immunoreactive neurons in the ventral nerve cord and the brain of the meal beetle Tenebrio molitor during postembryonic development

Summary By use of an antiserum against the crustacean cardioactive peptide (CCAP) several types of bilaterally symmetrical neurons have been mapped quantitatively in the ventral nerve cord and in the brain of the meal beetle, Tenebrio molitor. The general architecture of these neurons was reconstructed from peroxidase-antiperoxidase-labelled whole-mount preparations. From the subesophageal to the seventh abdominal ganglia two types of neurons show a repetitive organization of contralateral projection patterns in each neuromere. The first type has few branches in the central neuropil and a distinct peripheral projection. The second type is characterized by an elaborate central branching pattern, which includes ascending and descending processes. Some of its peripheral branches were found to supply peripheral neurohemal areas. In the protocerebrum, 10 CCAP-immunoreactive neurons occur with projections into the superior median protocerebrum and the tritocerebrum. Immunopositive neurons were mapped in larval and various pupal stages, as well as in the adult. All types of identified neurons were found to persist throughout metamorphosis maintaining their essential structural and topological characteristics. The CCAP-immunoreactive neurons of T. molitor are compared with those described for the locust. Putative structural homologies of subsets of neurons in both species are discussed.     

Distribution and morphology of descending brain neurons in the cricket Gryllus bimaculatus

The number and distribution of descending brain neurons have been investigated in the cricket. The results are based on retrograde labeling of these cells with either Lucifer yellow or Neurobiotin via whole or small split portions of the cervical connectives. Various groups of cells and single neurons have been identified, and the morphology of more than 40 cells is described. Nearly 200 descending brain neurons can be stained via one cervical connective. Their perikarya are concentrated in clusters that occur ipsi- and contralateral to the filled connective and that lie dorsal and ventral in the brain. Descending cells only arborize in the nonglomerular neuropils of the brain and never branch in the optic lobe. Cells descending ipsilaterally never arborize in the contralateral hemisphere, whereas contralateral descending neurons often branch in both hemispheres. Irrespective of soma position, cells can arborize in the ventral and/or dorsal neuropils of the brain. Neurons with somata in the protocerebrum often have branches in the deutocerebrum and vice versa. The main arborizations of the cells from the prominent ventral i5 group are found in the same part of the protocerebrum. In contrast, various cells arborize in the ventral posterior deutocerebrum, but their somata are not located in different clusters. Thus, neurons from the same cluster may, but need not necessarily, arborize in the same brain area.     

Physiological mismatching between neurons innervating olfactory glomeruli in a moth

The primary olfactory centres of most vertebrates and most neopteran insects are characterized by the presence of spherical neuropils, glomeruli, where synaptic interactions between olfactory receptor neurons and second-order neurons take place. In the neopteran insect taxa investigated so far, receptor neurons of a specific physiological identity target one glomerulus and thus bestow a functional identity on the glomerulus. In moths, input from pheromone-specific receptor neurons is received in a male-specific structure of the antennal lobe, called the macroglomerular complex (MGC), which consists of a number of specialized glomeruli. Each glomerulus of the complex receives a set of peripheral sensory afferents that encode one of several compounds involved in sexual communication. The complex is also innervated by dendritic branches of antennal lobe output neurons called projection neurons, which transfer information from the antennal lobe to higher centres of the brain. A hypothesis stemming from earlier work on moths claims that the receptor neuron innervation pattern of the MGC should be reflected in the pattern of dendrites of projection neurons invading the different MGC glomeruli. In this study we show that in the noctuid moth Trichoplusia ni, as in several other noctuid moth species, this hypothesis does not hold. The degree of matching between axon terminals of receptor neurons and the dendritic branches of identified projection neurons that express similar physiological specificity is very low.     

Crustacean cardioactive peptide-immunoreactive neurons innervating brain neuropils,retrocerebral complex and stomatogastric nervous system of the locust,Locusta migratoria

The distribution and morphology of crustacean cardioactive peptide-immunoreactive neurons in the brain of the locust Locusta migratoria has been determined. Of more than 500 immunoreactive neurons in total, about 380 are interneurons in the optic lobes. These neurons invade several layers of the medulla and distal parts of the lobula. In addition, a small group of neurons projects into the accessory medulla, the lamina, and to several areas in the median protocerebrum. In the midbrain, 12 groups or individual neurons have been reconstructed. Four groups innervate areas of the superior lateral and ventral lateral protocerebrum and the lateral horn. Two cell groups have bilateral arborizations anterior and posterior to the central body or in the superior median protocerebrum. Ramifications in subunits of the central body and in the lateral and the median accessory lobes arise from four additional cell groups. Two local interneurons innervate the antennal lobe. A tritocerebral cell projects contralaterally into the frontal ganglion and appears to give rise to fibers in the recurrent nerve, and in the hypocerebral and ingluvial ganglia. Varicose fibers in the nervi corporis cardiaci III and the corpora cardiaca, and terminals on pharyngeal dilator muscles arise from two subesophageal neurons. Some of the locust neurons closely resemble immunopositive neurons in a beetle and a moth. Our results suggest that the peptide may be (1) a modulatory substance produced by many brain interneurons, and (2) a neurohormone released from subesophageal neurosecretory cells.     

Pyrokinin/PBAN-like peptides in the central nervous system of mosquitoes

The pyrokinin/pheromone biosynthesis activating neuropeptide (PBAN) family of peptides is characterized by a common C-terminal pentapeptide, FXPRLamide, which is required for diverse physiological functions in various insects. Polyclonal antisera against the C-terminus was utilized to determine the location of cell bodies and axons in the central nervous systems of larval and adult mosquitoes. Immunoreactive material was detected in three groups of neurons in the subesophageal ganglion of larvae and adults. The corpora cardiaca of both larvae and adults contained immunoreactivity indicating potential release into circulation. The adult and larval brains had at least one pair of immunoreactive neurons in the protocerebrum with the adult brain having additional immunoreactive neurons in the dorsal medial part of the protocerebrum. The ventral ganglia of both larvae and adults each contained one pair of neurons that sent their axons to a perisympathetic organ associated with each abdominal ganglion. These results indicate that the mosquito nervous system contains pyrokinin/PBAN-like peptides and that these peptides could be released into the hemolymph. The peptides in insects and mosquitoes are produced by two genes, capa and pk/pban. Utilizing PCR protocols, we demonstrate that products of the capa gene could be produced in the abdominal ventral ganglia and the products of the pk/pban gene could be produced in the subesophageal ganglion. Two receptors for pyrokinin peptides were differentially localized to various tissues.     

Serotonin-immunoreactive neurons in the median protocerebrum and suboesophageal ganglion of the sphinx moth Manduca sexta

Summary Serotonin-immunoreactive neurons in the median protocerebrum and suboesophageal ganglion of the sphinx moth Manduca sexta were individually reconstructed. Serotonin immunoreactivity was detected in 19–20 bilaterally symmetrical pairs of interneurons in the midbrain and 10 pairs in the suboesophageal ganglion. These neurons were also immunoreactive with antisera against DOPA decarboxylase. All major neuropil regions except the protocerebral bridge are innervated by these neurons. In addition, efferent cells are serotonin-immunoreactive in the frontal ganglion (5 neurons) and the suboesophageal ganglion (2 pairs of neurons). The latter cells probably give rise to an extensive network of immunoreactive terminals on the surface of the suboesophageal ganglion and suboesophageal nerves. Most of the serotonin-immunoreactive neurons show a gradient in the intensity of immunoreactive staining, suggesting low levels of serotonin in cell bodies and dendritic arbors and highest concentrations in axonal terminals. Serotonin-immunoreactive cells often occur in pairs with similar morphological features. With one exception, all serotonin-immunoreactive neurons have bilateral projections with at least some arborizations in identical neuropil areas in both hemispheres. The morphology of several neurons suggests that they are part of neuronal feedback circuits. The similarity in the arborization patterns of serotonin-immunoreactive neurons raises the possibility that their outgrowing neurites experienced similar forces during embryonic development. The morphological similarities further suggest that serotonin-immunoreactive interneurons in the midbrain and suboesophageal ganglion share physiological characteristics.Abbreviations CNS central nervous system - DDC DOPA decarboxylase - LAL lateral accessory lobe - SLI serotonin-like immunoreactivity - SOG suboesophageal ganglion - VLP ventro-lateral protocerebrum     

Projections of auditory ventral-cord neurons in the supraesophageal ganglion ofLocusta migratoria

Summary The neuropile regions in the supraesophageal ganglion ofLocusta migratoria were revealed by Bodian staining of frontal and parasagittal sections.A combined recording and staining technique (CoS method, Rehbein et al., 1974) was used to identify physiologically five different types of auditory ventral cord neurons and mark the course of their axons and the positions of the terminal arborizations. The boundaries of the projection regions are described; they include the various multimodal neuropile regions in the ventrolateral protocerebrum.Previously demonstrated instances of convergence with neurons of other sensory systems, and others likely to exist, are considered with respect to their possible significance in neuronal processing within the auditory system.Supported by the Deutsche Forschungsgemeinschaft, as part of the program Sonderforschungsbereich Bionach, Bochum. The investigations were done at Lehrstuhl für Allgemeine Zoologie, Ruhr-UniversitÄt, D-4630 Bochum     

Descending brain neurons in the cricket Gryllus bimaculatus (de Geer): auditory responses and impact on walking

The activity of four types of sound-sensitive descending brain neurons in the cricket Gryllus bimaculatus was recorded intracellularly while animals were standing or walking on an open-loop trackball system. In a neuron with a contralaterally descending axon, the male calling song elicited responses that copied the pulse pattern of the song during standing and walking. The accuracy of pulse copying increased during walking. Neurons with ipsilaterally descending axons responded weakly to sound only during standing. The responses were mainly to the first pulse of each chirp, whereas the complete pulse pattern of a chirp was not copied. During walking the auditory responses were suppressed in these neurons. The spiking activity of all four neuron types was significantly correlated to forward walking velocity, indicating their relevance for walking. Additionally, injection of depolarizing current elicited walking and/or steering in three of four neuron types described. In none of the neurons was the spiking activity both sufficient and necessary to elicit and maintain walking behaviour. Some neurons showed arborisations in the lateral accessory lobes, pointing to the relevance of this brain region for cricket audition and descending motor control.     

Noctuid migration in Texas within the nocturnal aeroecological boundary layer

Long-distance migration of adult corn earworm moths (Helicoverpazea), and several other noctuid moth species, facilitates seasonalexpansion of pest populations and consequent increased infestationsof agricultural crops on a continental scale in North America.Long-term field studies of population dynamics and migratoryflights of H. zea and fall armyworm (Spodoptera frugiperda)in the United States were evaluated using X-band radar observationsand profiles of atmospheric conditions. These studies identifiedcharacteristic patterns of migratory flight that are largelyassociated with vertical profiles of temperature and wind speed.Collective patterns of moth migrations were generally highlycorrelated with wind headings, but often at a significant angulardeviation. Preliminary analyses are presented between moth distributionsin the aerosphere estimated from discrete moth counts usingX-band radar and bulk reflectivity data from NEXRAD Dopplerradar. Identification of associations between atmospheric factorsand noctuid population dynamics and migratory flights will improvethe ability to predict infestations by pest species throughouttheir broad seasonal range expansion.     

Central branchings of three sensory axons from a moth ear (Agrotis segetum, Noctuidae)

The central branchings of the sensory neurons in the noctuid moth ear have been investigated by introducing cobalt chloride through the cut ends of their axons. Three sensory axons stained, corresponding to the two auditory neurons (A cells) and the B neuron. The three axons were identified using physiological criteria. All three cells share the same basic morphology. Their axons divide into anterior and posterior branches, which contain numerous side branches. Their profiles lie ipsilateral, but A₁ gives off some fine side branches that cross the midline. The profiles of A₁ and B extend throughout all three thoracic ganglia, occupying a ventral, medial position. The branchings of A₂ remain within the meso- and metathoracic ganglia occupying a more dorsal and lateral position. We compare our results with those of an earlier anatomical study, and discuss them in relation to described interneurones and to behaviour     

Noctuidonema dibolia n. sp. (Aphelenchida: Acugutturidae), an Ectoparasite of the moth Mocis latipes (Lepidoptera: Noctuidae)

Noctuidonema dibolia n. sp., an ectoparasite of adults of the noctuid moth Mocis latipes (Guenée) is described. The differentiating characters are a club-shaped body with a subterminal vulva in the female, spicules with a reduced matrix and sheath and closely apposed dorsal and ventral arms in the male, very long stylet and conus, moderately prominent stylet knobs, a bluntly rounded head, and a large renette cell in both sexes. Lateral fields, rectum, anus, bursa, and gubernaculum are absent. Noctuidonema dibolia differs from the other species of the subfamily Noctuidonematinae in the size and robustness of the body, the length of the stylet and conus, the length of the tail, and the shape of the spicules.     

Auditory input to motor neurons of the dorsal longitudinal flight muscles in a noctuid moth (Barathra brassicae L.)

Summary Motor neurons innervating the dorsal longitudinal muscles of a noctuid moth receive synaptic input activated by auditory stimuli. Each ear of a noctuid moth contains two auditory neurons that are sensitive to ultrasound (Fig. 1). The ears function as bat detectors. Five pairs of large motor neurons and three pairs of small motor neurons found in the pterothoracic ganglia innervate the dorsal longitudinal (depressor) muscles of the mesothorax (Figs. 2 to 5). In non-flying preparations the motor neurons receive no oscillatory synaptic input. Synaptic input to a cell resulting from ultrasonic stimulation is consistent and can be either depolarizing or hyperpolarizing (Figs. 6 to 9). Quiescent neurons only rarely fire a spike in response to auditory inputs. Motor neurons in flying preparations receive oscillatory synaptic drive from the flight pattern generator and usually fire a spike for each wingbeat cycle (Figs. 10 to 12). Ultrasonic stimulation can provide augmented synaptic drive causing a neuron to fire two spikes per wingbeat cycle thus increasing flight vigor (Fig. 11). The same stimulus presented on another occasion can also inhibit spiking in the same motor neuron, but the rhythmic drive remains (Fig. 12). Thus, when the flight oscillator is running auditory stimuli can modulate neuronal responses in different ways depending on some unknown state of the nervous system. Sound intensity is the only stimulus parameter essential for activating the auditory pathway to these motor neurons. The intensity must be sufficient to excite two or three auditory neurons. The significance of these responses in relation to avoidance behavior to bats is discussed.     

Olig3 Is Not Involved in the Ventral Patterning of Spinal Cord

At embryonic stages, Olig3 is initially expressed in the dorsal-most region of the spinal cord, but later in the ventral marginal zone as well. Previous studies indicated that Olig3 controlled the patterning of dorsal spinal cord and loss of Olig3 function led to the re-specification of dI2 and dI3 neurons into dI4 interneurons. However, the role of Olig3 in regulating the development of ventral spinal cord has remained unknown. BrdU labeling demonstrated that ventral Olig3 was expressed in the post-mitotic neurons and Olig3+ cells seen at late embryonic stages were born at the earlier stage but remained in the marginal zone throughout embryogenesis. Loss-of-function and gain-of-function experiment indicated that Nkx2.2 regulated the expression of Olig3 in V3 interneurons. However, Olig3 mutation didn’t apparently affect the generation and migration of ventral neurons. These findings suggest that Olig3 plays different roles in regulating the development of dorsal and ventral spinal cord.     

The Organ of Bellonci in Ostracodes: An Ultrastructural Study of the Rod-shaped,or Frontal,Organ

Ultrastructural observations of the rod-shaped organ in Cypridina norvegica and Paraconchoecia elegans indicate homology with the organ of Bellonci of other crustaceans. In C. norvegica the organ is situated close to the ventral cup of the nauplius eye. Distally in the organ, several ciliary ramifications of the sensory neurons protrude into internal cavities formed by bordering cells. Six dendrites, with cell bodies within and in front of the brain, form the proximally bifurcated nerve, which enters the protocerebrum in the region of the medullae terminales. In this species the organ represents the deep receptor of the organ of Bellonci complex. In P. elegans the external part of the organ is situated between the proximal parts of the antennulae. Four dendrites in two groups emerge from the protocerebrum. Distally, they form branching cilia that are in close contact which the cuticle of the organ, thus forming a receptor similar to the superficial receptor of the organ of Bellonci complex of other crustaceans. It is suggested that the terms frontal organ and rod-shaped organ be abandoned in favour of the term organ of Bellonci.     

Auditory neurones in the brain of the cricket Gryllus bimaculatus (De Geer): Ascending interneurones

Two types of auditory interneurone which ascend from the prothoracic ganglion to the brain in the cricket Gryllus bimaculatus (De Geer) are described. Intracellular recordings were made from the axons of the neurones in the brain under closed-field stimulus conditions and the recorded cells then stained with either cobalt or Lucifer Yellow. Both neurone types—the Plurisegmental ascending low frequency neurone 1 (PALF1), and the Plurisegmental ascending high frequency neurone 1 (PAHF1)—show response characteristics which would make them well suited to encoding the conspecific calling and courtship songs respectively. Further, the projection areas of both neurone types in the brain overlap those of previously identified intraganglionic interneurones, particularly in the anterior-ventral protocerebrum, and it is suggested that an auditory neuropile may exist in this region.     

Alkenyl sex pheromone analogs in the hemolymph of an arctiid Eilema japonica and several non-arctiid moths

The majority of moth species utilize compounds derived from de novo synthesized fatty acids as their sex pheromones (type I). In contrast, species belonging to two recently diverged moth families, Arctiidae and Geometridae, utilize alkenes and their epoxides, which are derived from dietary essential fatty acids (EFAs), as their sex pheromones (type II). In the latter species, EFAs are considered to be converted into alkenes, often after chain elongation, in specialized cells called oenocytes. These alkenes are transported through the hemolymph to the pheromone gland, from which they are secreted with or without further modifications. We confirmed that the appearance of EFA-derived alkenes in the hemolymph was closely associated with the completion of pheromone gland formation in an arctiid moth Eilema japonica. Analyses of the hemolymph of several moth species utilizing type-I sex pheromones demonstrated the occurrence of (Z,Z,Z)-3,6,9-tricosatriene (T23), a typical type-II component, in the hemolymph of a noctuid Mamestra brassicae and two crambids Ostrinia furnacalis and Ostrinia scapulalis. Our results demonstrated that moths utilizing type-I pheromones have the ability to synthesize type-II sex pheromones, and suggested that recently diverged groups of moths may have secondarily exploited EFA-derived alkenes as sex pheromones.     

Is the ecological belt zonation of the Swiss Alps relevant for moth diversity and turnover?

Mountain ecosystems are traditionally envisioned as elevational belts of homogenous vegetation, separated by intervening ecotones. Recent research has cast doubt on such predictable layering at least in animal communities. We test the link of two a priori defined ecological belt zonations to noctuid moth distributions in the Swiss Alps. Predictions, in particular, were a coincidence of proposed ecotones with increased range endpoint frequencies and with increased species turnover or species richness between equidistant elevational bands. Using >320,000 distributional records for >500 noctuid species, we found no support for these three predictions despite several contrasting analytical approaches. Concurrent with recently published vertebrate data, we conclude that simple ecological belt zonations are unrelated to the moth communities found along mountain slopes. Rather, species are distributed idiosyncratically following their specific niche requirements. Additional rigorous evidence, particularly comparing insect clades spanning a spectrum of host-plant relationships, may be required to support the relevance of the ecological belt concept in structuring mountain ecosystems beyond tree and plant communities.     

Light trap transects – a field method for ascertaining the habitat preferences of night-flying Lepidoptera, using Mythimna turca (Linnaeus 1761) (Lepidoptera: Noctuidae) as an example

The habitat associations of the noctuid moth Double Line Mythimna turca (Linnaeus 1761) were studied in three areas in Britain by setting up light traps equidistant along transects which passed through different habitat types. Counts were made of M. turca at each trap station and the results compared with the habitat present in the vicinity of each trap. The results using chi-square analysis indicate that the preferred habitats for M. turca are woodland and Pteridium aquilinum scrub, especially where the grasses Agrostis capillaris and Holcus mollis occur. The environmental factors affecting moth catches are discussed and chi-squared expectations are adjusted to take account of the different efficiency of light traps in open grassland and woodland situations. The light trap transect method is shown to be useful for moth species where little is known of their ecology and can be used to provide a straightforward insight informing additional targeted autecological studies. The methodology may be less suited to those species which occur at low density, are poorly attracted to light or are known to migrate.