Developmental changes of the antenna and its neurons in the silkworm,Bombyx mori,with special regard to larval-pupal transformation

The larval antenna of Bombyx mori has 13 sensilla and about 52 sensory neurons in its distal portion. The axons form two nerve cords which unite in the cranial hemocoel to supply the brain as the olfactory nerve. The antennal imaginal disc, which is a thick pseudostratified epithelium continuous with the antennal epidermis, thickens markedly during the 5th instar by rapid cell proliferation. At the prepupal stage cell proliferation ceases and the disc everts to form a large pupal antenna. Simultaneously, an extensive cell rearrangement occurs in the antennal epidermis and the disc tissue becomes much thinner because of the abrupt expansion of antennal surface area. The two larval nerve cords thin down markedly by degeneration of axons, but they do not disintegrate totally even after the onset of pupation. The epidermis of the larval antenna forms the distal portion of the pupal antenna, while the imaginal disc forms the more basal portion. Development to the adult antenna occurs almost immediately after the onset of pupation; many adult neurons appear in the simple epidermis facing toward the thick outer side of the newly formed pupal cuticle. By 12 hours after the onset of pupation, these neurons align themselves in many transverse rows which are the first sign of the adult antennal configuration. Addition of these neuronal axons to the once-thinned nerve cords causes resumed thickening of the cords during the first 24 hours and thereafter. Differentiation of adult sensilla begins in the next 24 hours and is almost completed at the third day of pupation, which requires a total of 10 days.     

Phenotypic plasticity in numbers of antennal chemoreceptors in a grasshopper: effects of food

Grasshoppers, Schistocerca americana, reared from hatching on artificial diet had fewer sensilla on the antennae in the final larval stage than insects reared on lettuce. This was true of basiconic and coeloconic sensilla (presumed olfactory) and trichoid sensilla (presumed gustatory). The degree of difference varied along the antenna and with sensillum type. Adding salicin to the diet restored the numbers of all types of sensillum to levels equal to, or approaching, those in lettuce-fed insects. The addition of some volatile compounds – carvone (monoterpene), chalcone (flavonoid), citral (monoterpene) and guaiacol (phenolic) – resulted in slight increases in number, but coumarin (phenylpropanoid) had no effect. None of the compounds, either singly or in combination, produced more sensilla than were present in plant-fed insects. Accepted: 26 January 1998     

Embryogenesis of peripheral nerve pathways in grasshopper legs. I. The initial nerve pathway to the CNS

The founding of the first nerve path of the grasshopper metathoracic leg was examined at the level of identified neurons, using intracellular dye fills, immunohistochemistry, Nomarski optics, and scanning and transmission electron microscopy. The embryonic nerve is established by the axonal trajectory of a pair of afferent pioneer neurons, the tibial 1 (Ti1) cells. Following a period of profuse filopodial sprouting, the Ti1 axonal growth cones, possessing 75- to 100-microns-long filopodia, navigate a stereotyped path across the limb bud epithelium to the base of the appendage and into the CNS. The Ti1 axons grow from cell to cell along a chain of preaxonogenesis neurons spaced at intervals along the pathway, forming dye-passing junctions with them. The contacted neurons subsequently undergo axonogenesis and follow the pioneer axons into the CNS. Later arising neurons project their axons onto the cell bodies of the chain, thereby establishing the principal branch points of the nerve. Among the later arising afferents are the sensory neurons of the femoral chordotonal and subgenual organs. The morphology of the adult nerve appears to be determined by the stereotyped positioning of neurons in the differentiating limb bud and by the resultant axonal trajectories established during the first 10% of peripheral neurogenesis.     

Structure and development of antennae in a moth,Manduca sexta

The antenna of the moth, Manduca sexta, comprises two small basal segments and a long (2 cm) flagellum, which is divided into nearly 80 annuli. The annuli bear cuticular scales and small sensory organs, sensilla. A trachea, a blood vessel, and two nerve trunks run through the lumen of the antenna and into the head. Sensilla are arranged in an orderly pattern that is repeated on each flagellar annulus. Each flagellum bears about 10⁵ sensilla, which contain about 2.5 × 10⁵ primary sensory neurons. Clumps of undifferentiated cells (imaginal disks), present in the larva, form pupal antennae during the larval-pupal molt. During the subsequent metamorphic development of the adult, cell divisions, changes in cell shape, and cellular differentiation transform pupal into adult antennae. Sensilla and scales arise and differentiate in the antenna during metamorphosis; regions in which sensilla and scales will arise can be recognized before overt differentiation occurs. All of the flagellar annuli develop synchronously. The dense innervation and neuronal simplicity of antennal flagella, as well as their synchronous development at a late and accessible stage in the animal's life cycle, suit them for studies of neuronal differentiation.     

What are and what are not imaginal discs: reevaluation of some basic concepts (Insecta, Holometabola).

Some general aspects of the concept of imaginal discs in the Holometabola are reevaluated. Their monolayer character and continuity with the surrounding epidermis are confirmed. Studies on the imaginal discs of the silkworm (Bombyx mori) and data from the literature show that the discs and their peripodial cells produce cuticle during larval life, as well as at metamorphosis. In B. mori it is demonstrated that adult and larval antennae are produced by the same cells or their progeny. The results also suggest that segments of the typically three-segmented larval antenna of Holometabola are not scape, pedicel, and one-segmented flagellum; at least segments 2 and 3 are of flagellar origin. Based on these and some additional facts it is argued that: (1) No larval organs are "replaced" at metamorphosis, but strict "sequential homology" is always maintained. (2) Imaginal discs are not undifferentiated structures destined to form the adult after larval breakdown, cannot be unambiguously defined, and do not represent qualitatively different epidermal structures. Classical imaginal discs (invaginated and present also in pre-final larval instars) arose several times independently and were not present in the larvae of ancestral Holometabola. (3) Since the disc cells are not undifferentiated and "embryonic" (if these words have a defined meaning at all), it is unreasonable to expect that the processes taking place in discs at metamorphosis would differ fundamentally from those occurring in other diploid metamorphosing epidermal cells.     

Molecular characterization of Pegarn: a <Emphasis Type="Italic">Drosophila</Emphasis> homolog of UNC-51 kinase

We have isolated and characterized the gene encoding a Drosophila melanogaster homolog of Caenorhabditis elegans UNC-51 (uncoordinated movement-51): Pegarn. Developmental Northern blot shows the Pegarn gene is expressed at all stages of development. The protein is detected throughout the Drosophila third instar larval central nervous system (CNS) in axons projecting out from the ventral ganglion and in the optic anlagen of the optic lobe. Heterozygous Pegarn mutant embryos show defects in larval axonal neuronal patterning, but survive to adulthood. Homozygous mutants have an even more deformed pattern of neuronal development and do not survive through the larval stages. The data from this research suggest the critical roles of Pegarn in CNS and PNS axonal formation in Drosophila melanogaster and indicates its similar role in other multicellular species.     

Antennal sensory system of Periplaneta americana L.

The morphology of the antennal hair-sensilla of Periplaneta americana, their distribution and frequency on the antennal flagellum have been examined by transmission- and scanning-electron microscopy. The types of sensilla were distinguished with respect to physiologically relevant criteria such as wall structure and number of sensory cells. Among the sensilla of the antenna of the adult male, long, single-walled sensilla with four sensory cells (types sw B), Probably responsible for reception of sexual pheromones, are most frequent, representing about 54% of the antennal sensilla. About half of these sensilla are newly-formed at the imaginal ecdysis; the other half are derived from the shorter type sw B sensilla of the nymphal antenna. Short type sw B sensilla are present in all larval stages of both sexes and in adult females as well. During the imaginal ecdysis of males, however, the length of these sensilla increases to double that found in nymphs. Dendritic branches also increase in number. During postembryonic development, the number of sensory fibers in the antennal flagellum increases nearly 20-fold, from 14,000 in the first larval instar to about 270,000 in the adult male. The greatest increase, approximately 90%, occurs during the last developmental stage.     

Larval legs of mulberry silkworm Bombyx mori are prototypes for the adult legs

Morphological diversity of leg appendages is one of the hallmarks of developmental evolution. Limbs in insects may develop either from their embryonic prototypes or from imaginal discs harbored inside the larva. Bombyx mori (B. mori), a Lepidopteran insect, develops adult wings from larval wing imaginal discs. However, it has been debated whether the adult legs of B. mori arise from imaginal discs or from the larval legs. Here we addressed how the larval legs relate to their adult counterparts. We present the morphological landmarks during early leg development. We used expression of developmental genes like Distalless and extradenticle to mark leg primordia. Finally, we employed classical excision approach to develop a fate map of the adult leg. Excision and ablation of thoracic legs along proximo-distal axis at various times during larval development resulted in the loss of corresponding adult leg segments. Our data suggest that B. mori legs develop from larval appendages rather than leg imaginal discs.     

Sensory Projections from Ectopic Appendages in an insect: Inherent Specificity and Influence of Location

Peripheral and central pathfinding by sensory axons from appendages was investigated in the fly Sarcophaga bullata . (a) Supernumerary appendages (haltere, wing, antenna and leg) were produced by imaginal disc transplantation at various ectopic sites, (b) Leg neuropil was deafferented by leg disc extirpation and in its place another leg disc was implanted. (c) The basal stalk of a leg disc connecting it with the thoracic ganglion was transected. Using cobalt chloride and HRP backfilling methods the pathways taken by the afferents from these experimentally altered appendages was examined. The results indicate that the larval nerves and the imaginal disc stalks act as guides for growing axons to locate their correct entry sites within the ventral ganglion. In the absence of these guides the axons follow any peripheral nerve, such as abdominal nerve, and enter the ganglion at inappropriate sites. However, within the ganglion they take particular routes, almost identical to those taken by axons from in situ appendages suggesting the existance of some kind of a labelled pathway. Deafferentation does not make the leg neuropil more attractive to ingrowing ectopic sensory axons.     

The influence of segmental compartmentalisation on the development of the larval peripheral nervous system in Drosophila melanogaster

Summary The peripheral nervous system of embryos homozygous for prd, ftz, en and bxd was examined for defects and transformations in the segment-specific pattern of sensilla and peripheral nerves. This analysis permitted me to assign a distinct subset of sensilla to any of the three genetically and morphologically defined compartments s, a and p of each segment. In the wild-type embryonic segments, sensory axons deriving from sensilla of different compartments form a part of the common peripheral nerves. In the composite segments of prd and ftz mutant embryos, subsets of sensilla of two neighbouring segments are combined. Nevertheless, the axons of sensilla of different segmental identity are able to fasciculate and to form afferent nerves, which connect in an apparently normal fashion to the central nervous system. It is concluded that in the Drosophila embryo compartmental and segmental identity of sensory organs has no influence on the trajectories of sensory axons.     

Structure and development of the larval visual system in embryos of Lytta viridana leconte (coleoptera,meloidae)

At hatching (252–264 hr. at 25 ± 0.5°C), the visual system in larvae of Lytta viridana consists of paired stemmata, stemmatal nerves, optic neuropiles, and inner and outer imaginal optic lobe anlagen. It originates between 64 and 72 hr. with invagination of an optic lobe primordium in the side of each protocephalic lobe. These primordia later differentiate into protocerebral ganglion cells and the imaginal optic lobe anlagen. Each stemma arises at 72 hr. from epidermis below and behind the optic lobe invagination and subsequently becomes cupshaped, closes over, and differentiates. At hatching, it consists of a planoconvex corneal lens, a corneagenous layer, and an everse retina of numerous, pigmented retinular cells, each with a terminal rhabdomere. Between 96 and 104 hr, proximal ends of the retinular cells grow posteromedially into a transverse, horizontal fold in the posterior wall of each optic lobe invagination and along its length to the protocerebral neuropile, which they contact by 112 hr. As the brain withdraws posteriorly within the head, these axons elongate correspondingly. Sheath cells of stemmata and stemmatal nerves descend either from protocerebral perineurium or the optic lobe primordia. Structure and development of the larval visual system in L. viridana are compared with those of other insects and its various components are shown to be homologous throughout the Insecta. However, the stemmata of this insect more closely resemble the atypical imaginal eyes of male scale insects than the photoreceptors of other holometabolous larvae–a similarity arising through convergence.     

伪鞘榕小蜂雌雄成虫触角感器的超微形态、分布及适生意义

伪鞘榕小蜂Sycoscapter trifemmensis是一种寄生于鸡嗉子榕间花期榕果的专性寄生蜂,雌雄两性繁殖策略分化明显,为更好理解和诠释雌蜂寄主定位和雄蜂配偶识别机制,有必要对两性的触角感器进行观察。运用环境扫描电镜观察,对比和探讨了伪鞘榕小蜂雌雄成虫的触角和触角感器类型、分布、数量及其生态适应性。结果表明:雌蜂触角鞭节由11鞭小节组成,总长817.82±33.23μm,分布有毛形感器、刺形感器(类型1)、锥形感器(类型1)、多孔板形感器(类型1)、栓锥形乳突状感器5类5种;雄蜂触角鞭节仅由6鞭小节组成,全长为雌蜂的1/3,且各节有明显的缩短和增粗特征,着生感器包括毛形感器、刺形感器(类型2和类型3)、锥形感器(类型1和类型2)、多孔板形感器(类型2)、腔锥形感器5类7种。雌蜂触角感器的数量与分布显著高于雄蜂,且同类型感器在雌蜂上具有明显的延伸、增粗、分支的特征,以板形感器和锥形感器最为突出。伪鞘榕小蜂雌雄成虫的触角及其感器有明显的性二型,特别是与化学信息识别相关的感器,反映了雌雄蜂在不同生态环境和繁殖压力下的形态分化、行为策略和生态适应。     

Development of the sensory system in larvae and pupae of Chaoborus crystallinus (DeGeer, 1776; Diptera, Chaoboridae): sensory cells, nerves and ganglia of the tail region

Using various microscopical techniques, we have studied changes in the sensory equipment and architecture of the peripheral nervous system (PNS) around the first metamorphic molt from larva to pupa in the phantom midge Chaoborus. The transparent larvae and pupae of this dipteran with ancestral features allow us to investigate sensilla and their central projections from whole-mount preparations of complete groups of segments. Each sensillum on the posterior larval and pupal segments was identified using its external shape and position, and the morphology of the abdominal ganglia and segmental nerves was investigated. In addition, retrograde fills with the carbocyanine dye DiI were used to trace the axonal paths of most of the extero- and proprioreceptors. These findings were combined to produce maps of the sensory elements of larval and pupal abdomens that were analyzed at three levels: seriality (homonomy), ontogenetic changes of individual sensilla, and homology of the PNS between different species. Comparison of different segments shows for both stages that primarily there is a homonomous basic design of the PNS, but segment-specific modifications are evident in segments 8-10. Comparison of corresponding larval and pupal segments shows that many sensilla retain their internal structure and axonal projections. However, their external cuticular parts are changed in relation to the different life habits of larvae and pupae. Furthermore, some sensilla are completely reduced during the pupal molt, especially those of the tenth segment which appears as a distinct larval structure (caenogenesis). Comparison between species indicates that despite the varying types of sensilla their basic segmental arrangement and their axonal trajectories are conserved.     

山茱萸蛀果蛾幼虫触角和口器感器的超微形态

【目的】探索寄主范围不同的蛀果蛾科(Carposinidae)幼虫感器之间是否存在差异。【方法】采用扫描电子显微镜观察了为害山茱萸Cornus officinalis Sieb. et Zucc.的单食性蛀果害虫--山茱萸蛀果蛾Carposina coreana Kim老熟幼虫触角和口器感器的超微形态。【结果】山茱萸蛀果蛾幼虫触角柄节未见感器分布, 梗节上有2个刺形感器和3个锥形感器, 鞭节上有1个栓锥感器和3个锥形感器。口器上共有6种感器： 刺形感器数量多, 分布广; 栓锥感器主要分布在颚叶、 下颚须和下唇须上; 指形感器位于内唇和下颚须端节侧缘; 锥形感器和板形感器仅存在于下颚上; 内唇感器为内唇所特有。【结论】蛀果蛾幼虫触角和口器的感器与寄主范围之间未发现严格的对应关系。     

Unusual pheromone receptor neuron responses in heliothine moth antennae derived from inter-species imaginal disc transplantation

Single-cell electrophysiological recordings were obtained from olfactory receptor neurons housed in sensilla trichodea along the adult antennae arising from transplantation of the antennal imaginal discs between larval male Helicoverpa zea and Heliothis virescens. The olfactory receptor neurons from the majority of type C sensilla sampled on transplanted antennae displayed response characteristics consistent with those of the species that donated the antennae. However, some of the sensilla type C sampled in either transplant type contained olfactory receptor neurons that responded in a manner typical of the recipient species or other neurons that have not previously been found in the type C sensilla of either species. The single-cell data help to explain behavioral results showing that some transplant males do fly upwind to both species' pheromone blends, an outcome not expected based on known antennal sensory phenotypes. Our results suggest that host tissue can influence antennal olfactory receptor neuron development, and further that because of a common phylogenetic ancestry the donor tissue has the genetic capability to produce a variety of sensillar and receptor types.     

Morphogenesis of the antenna of the male silkmoth, Antheraea polyphemus. V. Development of the peripheral nervous system

The imaginal antenna of the male silkmoth Antheraea polyphemus is a feather-shaped structure consisting of about 30 flagellomeres, each of which gives off two pairs of side branches. During the pupal stage (lasting for 3 weeks), the antenna develops from a leaf-shaped, flattened epidermal sac ('antennal blade') via two series of incisions which proceed from the periphery towards the prospective antennal stem. The development of the peripheral nervous system was studied by staining the neurons with an antibody against horseradish peroxidase as well as by electron microscopy. The epithelium is subdivided in segmentally arranged sensillogenic regions alternating with non-sensillogenic regions. Immediately after apolysis, clusters consisting of 5 sensory neurons each and belonging to the prospective sensilla chaetica can be localized at the periphery of the antennal blade in the sensillogenic regions. During the first day following apolysis, the primordia of ca. 70 000 olfactory sensilla arise in the sensillogenic regions. Axons from their neurons are collected in segmentally arranged nerves which run towards the CNS along the dorsal as well as the ventral epidermis and are enveloped by a glial sheath. This 'primary innervation pattern' is completed within the second day after apolysis. A first wave of incisions ('primary incisions') subdivide the antennal blade into segmental 'double branches' without disturbing the innervation pattern. Then a second wave of incisions ('secondary incisions') splits the double branches into single antennal branches. During this process, the segmental nerves and their glial sheaths are disintegrated. The axons are then redistributed into single branch nerves while their glial sheath is reconstituted, forming the 'secondary', or adult, innervation pattern. The epidermis is backed by a basal lamina which is degraded after outgrowth of the axons, but is reconstituted after formation of the single antennal branches.     

属模巨齿蛉成虫感器的超微形态

为了解属模巨齿蛉成虫多个部位感器的超微结构及其对生命活动的影响,本文对属模巨齿蛉成虫的触角、大颚、翅缘和生殖器4个部位进行了电镜扫描。研究发现,触角有7种感器,分别是毛形感器Ⅰ型、Ⅱ型、Ⅲ型、Ⅳ型、腔锥感器、锥形感器、柱形感器;大颚有3种感器,分别是腔锥感器、锥形感器、刺形感器;翅缘有4种感器,分别是毛形感器Ⅱ型、Ⅲ型、Ⅳ型、腔锥感器;雌性成虫生殖器有7种感器,分别是毛形感器Ⅱ型、Ⅲ型、Ⅳ型、Ⅴ型、Ⅵ型、锥形感器、钟形感器。柱形感器是触角的特殊感器,钟形感器是雌性成虫生殖器的特殊感器。毛形感器是触角、翅缘和生殖器主要感器,而大颚上没有毛形感器。触角和生殖器上的感器类型最多,且分布最密集,这与触角和生殖器对成虫的交配、产卵行为具有重要作用相吻合。     

长刺萤叶甲属与短鞘萤叶甲属的外部形态扫描电镜观察

本文对长刺萤叶甲属和短鞘萤叶甲属的头部,口器,触角,体毛,刻点,前胸背板,鞘翅缘折,足的外部形态首次进行了扫描电镜观察,并对结果进行了分析,比较,发现纬度变化引起的形态变异不显著,而海拔的变化引起形态的适应性变化比较显著。因此,对两种不同海拔的萤叶甲进行形态比较,研究萤叶甲在不同地理环境下,其形态的适应性变化提供了有价值的依据。     

灰茶尺蠖成虫触角及幼虫头部感器超微结构

【目的】明确灰茶尺蠖Ectropis grisescens成虫触角及幼虫头部感器的种类、形态、数量和分布,以探讨灰茶尺蠖的行为机制。【方法】利用扫描电镜技术观察灰茶尺蠖雌、雄成虫触角和5龄幼虫头部感器的超微结构。【结果】灰茶尺蠖成虫触角上分布有8种感器,分别是栓锥形感器、耳形感器、毛形感器(Ⅰ-Ⅳ)、B?hm氏鬃毛、腔锥形感器(Ⅰ和Ⅱ)、鳞形感器、锥形感器(Ⅰ和Ⅱ)和刺形感器。其中,栓锥形感器仅分布在雌蛾触角上,耳形感器、毛形感器(STⅠ-Ⅲ)仅分布在雄虫触角上。5龄幼虫触角上着生1个栓锥形感器、1个锥形感器和2个刺形感器;上唇着生有6对刺形感器,内唇着生有3对刺形感器和1对指形感器;上颚基部外侧着生有2个刺形感器;下颚及下颚须着生有5个刺形感器、9个锥形感器和2个栓锥形感器;下唇须着生有1个锥形感器和1个刺形感器;吐丝器前端着生有1对刺形感器。【结论】灰茶尺蠖雌、雄成虫触角感器存在性二型性,且雄虫上感器种类和数量较多,据此推测雄虫感受寄主植物或性信息素的能力较强;幼虫头部感器具有嗅觉和味觉功能,在其判断食物的种类和适应性等生态行为中发挥重要作用。