An accessory pulsatile organ located in the mesothoracic legs pumps hemolymph towards the tip of the leg ventrally and towards the body near the dorsal side. It consists of a muscle attached to the ventral side of the trochanter and to the central region of a transverse connective tissue diaphragm located at the trochanter-femur border. The diaphragm has a ventral outlet that permits efferent hemolymph flow through a narrow femoral sinus. A second dorsal outlet allows the afferent countercurrent back to the thorax through a separate hemolymph channel. During abdominal ventilation, the pumping rhythm of the leg-heart is neurally synchronized with abdominal ventilation. Expiratory pressure expands tracheal air sacs in the ventral trochanter and helps driving hemolymph out of this space. In idle periods of resting ventilation, an autonomous myogenic rhythm of the leg-heart can maintain hemolymph circulation in the mesothoracic leg without neural control. (C) 1999 Elsevier Science Ltd. All rights reserved.
The objective of the present article is to analyse the role of heartbeat and body movements in respiratory function in Galleria mellonella L. (Lepidoptera: Pyralidae) pupae with clear gas exchange cycles. We did not find any direct evidence of co-ordination between heartbeat and respiration or body movements and respiration. Cyclic CO2 output was independent of abdominal movements and heart pulsations during the entire pupal development. In young pupae, heart activity periods were independent of abdominal movements. In middle-aged pupae, there appeared a clear trend towards the coincidence of heartbeat periods with the periods of abdominal movements. In late pupae, the heart pulses and the contractions of body skeletal muscles were mostly synchronized. It may be suggested that the contractions of intersegmental somatic abdominal muscles support the heartbeat, and, in this way, the hemolymph flow is accelerated. The heart and circulatory action may facilitate gaseous diffusion in the tracheae.
The ultrastructure of the pericardial athrocytes of fifth instar tobacco hornworm Manduca sexta L. (Lepidoptera: Sphingidae) was examined by transmission electron microscopy. These cells are highly specialized for the maintenance of hemolymph homeostasis by synthesis and secretion of some proteins, and uptake and degradation of others. We observed a striking radial zonation with numerous labyrinthine channels extending into the cell providing a large surface area for enhanced efficiency of endocytosis. Granular material was imported into the endosomal compartment by fusion of endocytotic vesicles from the basal region. Anatomical evidence supports the hypothesis that proteins are transported from the endosome to the lysosome, by maturation of the early endosome to form the late endosome/lysosome, as opposed to vesicular transport. The presence of catalase in athrocyte lysosomes is reported for the first time. Endocytosis in the athrocytes of insects is compared with endocytosis in vertebrate systems.
Morphological structures of the head of 1st and 5th instar nymphs of Triatoma circummaculata and Triatoma rubrovaria were revealed by analysis using scanning electron microscopy (SEM). Differences between 1st and 5th instar nymphs of these two species were observed in the postocular callosity, the number of ommatidia and tapered hair, the small segment between antennal segments, the rostrum third segment and slit lines. These slit lines were different only in the 5th instar. Similarities observed were the presence of tapered hairs in the joints, and the type of sensilla in the antennal segments. Only the 1st instar shows anteclypeus and gena sensilla. The antennal segments comprise the following types of sensilla: basiconica, bristles type I, bristles type II, bristles type III, campaniformia, coeloconica, chemosensilla, placodea, trichobothria and trichoidea. We describe here for the first time six (3+3) sensilla basiconica on the dorsal portion of the first segment of the rostrum.
The typology, number and placement of antennal sensilla of the click beetle Melanotus villosus (Geoffroy) (Coleoptera: Elateridae) were studied using scanning electron microscopy. On both the males and females the antennae are made up of the scape, pedicel and nine flagellomeres. Two types of basiconic sensilla, three types of trichoid sensilla, one type of styloconic sensilla, one type of chetoid sensilla, dome-shaped sensilla, grooved pegs, and Böhm sensilla all appear on the antennae of the beetles of both sexes, with the exception of trichoid sensilla type II, whose large number (average of 1635 hairs per antenna) was found only in male beetles. Sensilla trichodea type II evidently respond to the sex pheromone produced by the female beetle. Unlike the other two click beetles, studied up till now, Agriotes obscurus and Limonius aeruginosus, the trichoid and basiconic sensilla of M. villosus, whose proven or assumed function is olfactory, are located predominantly on the flagellomeres ventral extensions. It is assumed that the placement of the olfactory sensilla, mainly on the ventral side of M. villosuss antennae, and their more or less even distribution on the flagellomeres, can be seen as morphological adaptation of this species of insect, whose specific behavioural reaction of olfactory searching is flying, both before and after contact with an odour plume.
The mushroom bodies of the insect brain are centers for olfactory and multimodal information processing and they are involved in associative olfactory learning. They are comprised of numerous (340,000 in the bee brain), small (3-8 mu m soma diameter) local interneurons, the Kenyon cells. In the brain of honeybees (Apis mellifera) of all castes (worker bees, drones and queens), wasps (Vespula germanica) and hornets (Vespa crabro) immunostaining revealed fibers with dopamine-like immunoreactivity projecting from the pedunculus and the lip neuropil of the mushroom bodies into the Kenyon cell perikaryal layer. These fibers terminate with numerous varicosities, mainly around the border between medial and lateral Kenyon cell soma groups. Visualization of immunostained terminals in the transmission electron microscope showed that they directly contact the somata of the Kenyon cells and contain presynaptic elements. The somata of the Kenyon cells are clearly non-immunoreactive. Synaptic contacts at the somata are unusual for the central nervous systems of insects and other arthropods. This finding suggests that the somata of the Kenyon cells of Hymenoptera may serve an integrative role, and not merely a supportive function. (C) 1999 Elsevier Science Ltd. All rights reserved.
In the blowfly Calliphora vicina (Diptera: Calliphoridae), the morphology of the dorsal vessel and of a new cephalic accessory pulsatile organ (CPO) were analysed with light-microscopic, SEM and TEM techniques. The CPO and neck aorta are reconstructed 3-dimensionally by computer-aided design. The pulse activity of the CPO and of the heart was measured in intact flies over periods of several hours or days using contact-thermography with laser beam heat-marking. The intratracheal pressure was simultaneously measured at the anterior thoracic spiracle. The dorsal vessel is constructed of pairs of left–right alternating cells. Its enlarged chamber in the anterior abdomen contains two pairs of incurrent ostia, its posterior narrower heart tube possesses three pairs of incurrent ostia and paired caudal excurrent openings. The aorta opens with a funnel-like opening in the neck. Proportions, arrangement and ultrastructure of the aorta, heart cells and pericardial muscles are described. Cushionlike sarcoplasmic protrusions of heart cells (pair no. 17) probably function as internal valves. The neck aorta is constructed of a cuticular ‘roof’ deviating from the dorsal neck membrane and a ventral longitudinal muscle ‘floor’. The aorta is not kept open because of missing muscle or connective tissue strands. The underside of the CPO is fused with air sacs that function as antagonists to the muscles. The heart reverses its beat periodically in resting and active flies. During the longer forward-pulse periods, mean frequency is lower (about 3.0 Hz at Ta 20°C), during the shorter backward periods mean frequency is higher (4.6 Hz). The CPO beats only during forward-pulse periods of the heart with an independent and slower pulse rate (1.8 Hz). The CPO-pulses produce positive pressure pulses at the anterior thoracic spiracle. During backward-pulse periods of the heart and pulse pause of the CPO, a continuous negative pressure arises at the thoracic spiracle instead of pressure pulses. The intimate connection of an accessory pulsatile organ with tracheal air sacs makes it work as a bifunctional pump for hemolymph distribution and tracheal ventilation. Neurosecretory and synapsing innervation of the CPO in connection with aorta, heart and pericardial septum muscle innervation suggest that both organs are regulated and that the duration of their periods is neuronally coordinated.
The surface and structure of the chorion of eggs of Diatraea saccharalis (F.) (Lepidoptera: Crambidae), Anticarsia gemmatalis (Huebner), Heliothis virescens F., Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae), Sitotroga cerealella (Oliver) (Lepidoptera: Gelechiidae), Ephestia kuehniella Zeller and Corcyra cephalonica Stainton (Lepidoptera: Pyralidae), that are hosts of Trichogramma galloi Zucchi and Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) were studied on SEM and TEM. Other characteristics of these eggs, such as changes in their color during embryonic development, size and volume were also recorded. Sculpturing and texture of the surface of the chorion greatly varied among the species studied, as well as the number of layers of the chorion and their thickness. Eggs of the factitious hosts were among the smallest and their volume was very close to each other. All these characteristics would provide basic information for a better understanding of the host selection behavior and are useful for the development of a suitable artificial host egg for the in vitro rearing of these egg parasitoids.
In non-diapausing pupae of the two birdwing butterfly species Troides rhadamantus and Ornithoptera priamus (Lepidoptera, Papilionidae) heart activity and CO2 release rates were measured simultaneously within the initial half of pupal development. Heartbeat patterns in these pupae consist of three different types of activity: Continuous forward-pulse periods of different duration with a frequency range of about 0.25–0.52 s−1, continuous backward-pulse periods with lower frequencies (0.15–0.29 s−1) and intermittent backward-pulse periods when short series of three to 10 single heartbeats at frequencies of 0.12–0.35 s−1 alternated with heart pauses of 2–10 min. CO2 release was discontinuous (CFO-type) from about four to 12 days after pupation in Troides rhadamantus and from about four to 18 days in Ornithoptera priamus. Mean CO2 release rates were very low in both species (10–30 nmol g−1 min−1). After this period, heart pauses occurred more frequently, probably indicating the onset of metamorphosis and the beginning partial histolysis of the heart. Infrared-optical and thermometrical measurements of heartbeat indicated that haemolymph transport within the dorsal vessel in forward direction is more effective than in backward direction. This is deduced from the higher heartbeat frequency and heartbeat amplitude of the forward pulsations. Results from ultrasonic doppler velocimetry suggest that haemolymph flow velocity is highest during the relatively long diastasis of 2–3 s (30–40 mm s−1), while minimum particle speed (about 20 mm s−1) is at the end of systole and the beginning of diastole. This would mean that haemolymph velocity is highest between two consecutive peristaltic waves. In contrast to the haemolymph velocity, the speed of the peristaltic wave measured with the infrared transmission technique was lower (about 8.4–22 mm s−1 in Troides, 10–23 mm s−1 in Ornithoptera) and remained constant during forward pulse periods. During backward beating the speed was lower (8–20 mm s−1 in Troides, 9–17 mm s−1 in Ornithoptera) and decreased during backward pulse periods. During day two to seven in Troides and day three to nine in Ornithoptera, spiracular opening periods coincided with changes in heartbeat direction from backward to forward pulsations. A possible influence is the more efficient convective haemolymph mixing in the haemocoel during forward heartbeat. The mixing allows to bring the haemolymph in close contact with the tracheal system where the discharge of CO2 takes place. Heartbeat may therefore serve for shortening the diffusion pathways for a rapid transition into the tracheal system during the open period of the spiracles.
Gynandromorphic honey bees, Apis mellifera (Hymenoptera: Apidae), were examined to determine characteristic morphological and anatomical features of the antennal system. The antennae of gynandromorphic individuals are predominantly worker or drone-like. Hybrid antennae, composed of female and male tissues, occur only rarely (7 out of 188 examined antennae). Depending on the mosaic pattern of the head, both antennae can be drone-like or worker-like, or one can be drone-like and the other worker-like. Examination of the antennal lobes of six characteristic specimens revealed that antennal lobes, which are innervated by drone-like antennae, always have drone-specific enlarged tracts and macroglomerular complexes, whereas antennal lobes innervated by worker-like antennae always are composed of normally sized glomeruli. Thus, there is a strict correlation between the sexual morphology of the antennae and the sexual organization of the antennal lobe neuropil. In one antennal lobe, innervated by a hybrid antenna, we found a hypertrophied glomerulus, certainly homologous to one of the macroglomerular complexes in drone-like antennal lobes.jy 1999 Elsevier Science Ltd. All rights reserved.
The monoclonal antibody BrH1, specific for hemocytes of the stick insect Bacillus rossius, was employed to study the appearance of hemocytes during embryogenesis. Laid eggs were collected for eight weeks, and cryosections were probed with the antibody. First positive cells were detected at the fifth week, and increased in number onwards. No peculiar differences were observed in the overall morphology between embryonic and non-embryonic hemocytes.
The antennal circulatory organs of 38 species of Hymenoptera were investigated by means of serial semithin sections, SEM and TEM. In Apis, this organ consists of an unpaired ampulla from which blood vessels that extend into the antennae originate. The ampulla is a very delicate structure of elastic connective tissue. Its lumen communicates with the head hemocoel via numerous perforations in its wall. No specific ampulla muscles exist; contraction of pharynx dilators causes compression of the ampulla, whereby hemolymph is forced into the antennae.An absence of directly-acting muscles is common to the functional morphologies of the antennal circulatory organ in all investigated Hymenoptera. Some anatomical characters of this organ, however, vary among taxa: (i) presence of one or two ampullae, (ii) optional dorsal hemolymph channel, which connects the ampulla with the dorsal vessel, (iii) optional ampulla pumping case formed by cuticular apophyses, and (iv) differences in shape and number of the ampulla openings. The distribution of these characters is discussed along the current views on the phylogeny of Hymenoptera. Comparison with other insect orders indicates an autapomorphic status for the basic functional morphology of the antennal circulatory organ in Hymenoptera. (C) 1999 Elsevier Science Ltd. All rights reserved.
Our knowledge about the morphology of neurons innervating the lateral cardiac nerve cords (LCNCs) in migratory locusts, Locusta migratoria migratorioides (R. and F.) (Orthoptera, Acrididae) has increased considerably during recent years, mainly owing to immunocytochemical studies using antisera directed against members of insect neuropeptide families. In principle, there are three morphological types of neurons located within the CNS, which innervate the LCNCs in locusts: abdominal ganglia contain (i) bilaterally projecting, possibly unpaired neurons (BPNs) and (ii) paired, unilaterally projecting neurons. In addition, (iii) the LCNCs receive innervation from a pair of neurons, which is located within the suboesophageal ganglion. The axons of all three types of neurons project into the LCNCs via the segmental heart nerves, the most distal extensions of the dorsal segemental nerves of abdominal ganglia. When estimating the number of axons contained in one segmental heart nerve and formed by all central neurons so far identified, this number exceeds the number of axon profiles previously seen using the electron microscope. This indicates that most, or perhaps all central neurons projecting into the LCNCs, have been identified in these insects.
Copulatory mechanisms and internal reproductive systems of male and female Plutella xylostella (L.) were investigated. Both male and female specimens exhibited characteristics typical of ditrysian Lepidoptera, with some peculiarities. Female structures appear to be relatively simple: the bursa copulatrix lacks cuticular signa within, the spermatheca lacks lagenar arms exhibited in some Lepidoptera, and colleterial glands have secretory system and reservoir combined. Male accessory gland ducts are joined distally, a condition that has not been described in other Lepidoptera. Genitalia of both sexes appear simple; females possess a posterior cuticular extension of abdominal sternites that houses the bursal duct and accomodates the needle-like aedeagus of a male during copulation. Despite the apparent simplicity, configuration of genitalia is highly specific in shape, angle, and size, which is likely to be important in maintaining reproductive isolation within the species. However, a population of P. xylostella from Australia showed some modification to both aedeagal and bursal structures. These variations suggest some important implications for considering species with worldwide distributions.
The external morphology of the cuticular spines, and the ultrastructure of the spines and neck gland in fifth instar Abananote hylonome larvae was studied. The larvae are spiny along the length of their bodies. Along the length of the spines are setae with a swelling towards the apical region. Internally, in the base of each seta there is a complex of secretory cells surrounding a large vacuole continuous with the seta. The neck gland is eversible, composed of a pair of oval internal sacks connected to the exterior via an extracellular canal produced by an invagination of the cuticle. The sack cells surround a reservoir containing an amorphous substance. In both the spines and neck gland the nuclei are large and irregularly shaped, typical of defensive glands of Lepidoptera. The border of the cells adjacent to the vacuoles (spines) and the reservoir (neck gland) is made up of numerous microvilli. We suggest that defensive compounds are produced in the gland cells and then later released via the vacuoles in the spines and the extracellular canal in the neck gland.
The ultrastructure and distribution of sensilla on the antennae of the cabbage stem flea beetle, Psylliodes chrysocephala, were investigated using scanning and transmission electron microscopy techniques. Eight different sensillar types were distinguished. These were; hair plate sensilla, sensilla chaetica, three types of sensilla trichodea, sensilla basiconica, grooved peg sensilla and styloconic sensilla. The sensilla chaetica are known to be gustatory receptors. Ultrastructure indicates that the hair plate sensilla and sensilla trichodea type one are probably mechanoreceptors, whilst the sensilla styloconica are probably thermo-hygro receptors. These thermo-hygroreceptors are unusual in that they are innervated by two sensory cells (one hygroreceptor and one thermoreceptor) rather than the more usual triad. The remaining four sensillar types all have a porous hair shaft, indicating an olfactory role. One of these (the grooved peg sensillum) may also have a thermoreceptive function. No sexual dimorphism was found in the structure, number or distribution of the antennal sensilla.
The morphology, ultrastructure, and innervation of the spiracles of the instars and adults of representatives of three lepidopteran families were examined: Ornithoptera priamus poseidon and Pachliopta aristolochiae (Papilionidae), Attacus atlas (Saturniidae), and Acherontia atropos (Sphingidae). Peritreme and atrium show stage- and family-specific structures for protecting the internal valve apparatus. The gross morphology of the cuticular valve mechanism is uniform within the three families, consisting of a rigid bow and a movable bar with a lever. In adult Papilionidae, all cuticular parts (bow, bar and lever) of the valve are innervated by multipolar dendrites. Internal or external cuticular chemo- or hygroreceptors, which could participate in the regulation of respiration, could not be detected in any stage. The closing muscle inserts between the tip of the lever and the base of the bar, and is innervated only by motor neurons. The elasticity of the cuticular system and an opener are the antagonists to the closing muscle. The spiracular opener of the adult Papilionidae and of all instars of the moths is an elastic ligament. The opener of the larval and pupal spiracles of the Papilionidae, however, is a single thickened muscle fiber surrounded by an elastic sheath of connective tissue. As it contains motor and multipolar sensory neurons, we assume that it may function as a stretch receptor for controlling the spiracular opening state.
The development and the ultrastructural changes of the suboesophageal body were studied during embryogenesis of Locusta migratoria (Orthoptera : Acrididae). The suboesophageal body develops from the mandibular coelomic cavities. It differentiates early, before the completion of germ band segmentation (stage IIIc), the other mesodermal cells remaining undifferentiated. The cells of the suboesophageal body rapidly develop a structure similar to that of nephrocytes. They consist of a peripheral transfer zone and a perinuclear zone, the site of synthesis and storage. Material absorbed by endocytosis is taken up by α-vacuoles, then stored in β-vacuoles. Golgi vesicles, tubules and vesicle complexes may be involved in the secretory activity of the cells. The activity of the suboesophageal body is maximal until stage VI, after katatrepsis, after which degeneration begins. Very few cells remain at eclosion and they are completely degenerated. The suboesophageal body may be involved in the regulation of embryonic haemolymph composition, and it develops according to its function. The suboesophageal body differentiates early and is thus functional when the haemolymph first forms in the subgerminative space. It degenerates after the differentiation of the pericardial cells and the fat body, which regulate haemolymph composition.
Insect embryo development is a complex process which requires nuclear and cellular division, cell shape alteration, and cell movement. This process needs to be orchestrated in a specific spatial and temporal fashion. Different insect species, despite similarities, present distinct morphogenetic pathways. We used the dipteran R. americana as a comparative model for embryo morphogenesis studies, following embryo development with different histochemical and immunohistochemical procedures. Despite the phylogenetic proximity with D. melanogaster, R. americana presents a peculiar morphogenesis. We show that at the initial phases of development, from egg fertilization to blastoderm formation, R. americana is similar to Drosophila. The first cleavages are nuclear and cellularization only begins after nuclei spread throughout the egg’s cortex. However after this stage a series of cell movements establishes a short compact germ band anlage, which gastrulates in a pattern quite different from Drosophila. After gastrulation the germ band elongates anterior–posteriorly and segmentation occurs simultaneously along the embryo. Embryo development from egg fertilization to larva hatching takes about 12 days. Our results show that R. americana presents a different morphogenetic pathway which does not fit in the current short, intermediate or long germ band classification.
The spermatozoa of Bephratelloides pomorum are very long and fine. Each spermatozoon measures about 620 mu m in length by 0.38 mu m in diameter and, when seen under the light microscope, appears to be wavy along its entire length. The head, which is approximately 105 mu m, comprises a small acrosome and a nucleus. The acrosome is made up of a cone-shaped acrosomal vesicle surrounding the perforatorium and the anterior end of the nucleus. Innumerable filaments radiate from it. The perforatorium has a diameter equal to that of the nucleus at their junction, where it fits with a concave base onto the rounded nuclear tip. The nucleus is helicoidal and completely filled with homogeneous compact chromatin. It is attached to the tail by a very long and quite electron-dense centriolar adjunct that extends anteriorly from the centriole in a spiral around the nucleus for approximately 8.5 mu m. The tail consists of an axoneme with the 9+9+2 microtubule arrangement pitched in a long helix, as well as a pair of spiraling mitochondrial derivatives (with regularly arranged cristae) that coil around the axoneme, and two small accessory bodies. As well as the spiraling of the nucleus, mitochondrial derivatives and axonemal microtubules, the sperm of B. pomorum present other very different morphological features. These features include the acrosome and centriolar adjunct, both of which differentiate the spermatozoa from the majority of sperm found in other Hymenoptera. In addition these structural variations demonstrate that the sperm of chalcidoids provide characteristics that can certainly prove useful for future phylogenetic analysis at the subfamily level and, possibly, the genus too. (C) 2000 Elsevier Science Ltd. All rights reserved.
