An ultrastructural analysis of the ecdysoneless ((l(3)ecd 1ts) ring gland during the third larval instar of Drosophila melanogaster

Summary In the late third larval instar of Drosophila melanogaster, the prothoracic gland, an endocrine portion of the ring gland, synthesizes ecdysteroids at an accelerated rate. The resultant ecdysteroid titer peak initiates the events associated with metamorphosis. The normal prothoracic gland displays several ultrastructural features at this developmental stage that reflect increased steroidogenic activity, including extensive infoldings of the plasma membrane (membrane invaginations) and an increase in both the concentration of smooth endoplasmic reticulum (SER) (or transitional ER) and elongated mitochondria. By contrast, the prothoracic glands of larvae homozygous for a conditional larval lethal mutation, l(3)ecd ^1ts, not only fail to produce ecdysteroids at normal levels at the restrictive temperature (29° C), but also acquire abnormal morphological features that reflect the disruptive effects of the mutation. These abnormalities include an accumulation of lipid droplets presumed to contain sterol precursors of ecdysteroids, a disappearance of SER and a drastic reduction of membrane invaginations in the peripheral area of the cell. These morphological defects are observed in prothoracic glands dissected from larvae transferred from 18° C to 29° C approximately 24 h before observation and also within 4 h of an in vitro transfer to 29° C following dissection from wandering third instar larvae reared at 18° C. No ultrastructural abnormalities were noted in the corpus allatum portion of mutant ring glands. These observations further indicate the direct involvement of the ecd gene product in ecdysteroid synthesis and suggest a role for the gene in the proper transport of precursors to the site where they can be utilized in ecdysteroid biosynthesis.     

An ultrastructural and developmental analysis of the corpus allatum of juvenile hormone deficient mutants ofDrosophila melanogaster

Summary The ultrastructure of the corpus allatum of theapterous mutantsap ⁴ andap ^56f ofDrosophila melanogaster during larval-pupal-adult metamorphosis and adult life was correlated with the gland's ability to synthesize juvenile hormone in vitro. During the early wandering period of the third instar of both mutants, a high concentration of smooth endoplasmic reticulum, mitochondria and mitochondrion-scalariform junction complexes are typical features of an active corpus allatum cell. Juvenile hormone biosynthesis by the glands is high at that time and, in fact, only slightly lower than that of wild type glands. In contrast to the wild type gland, the cells of the pupal and pharate adult corpus allatum of both mutants contains highly electron dense mitochondria with tubular cristae but no whorls of smooth endoplasmic reticulum nor glycogen clusters. The frequency and size of the lipid droplets, putatives depots of the juvenile hormone precursors, in cells of theap ^56f gland is a function of the insect's age, but both are lower than in wild type gland cells. Juvenile hormone biosynthesis by both mutant glands remains at the basal level when compared to increased synthesis by the wild type gland. The frequency and density of lipid droplets in cells of theap ⁴ corpus allatum are much lower than in theap ^56f glands. During adult life, the ultrastructural profile of theap ^56f corpus allatum is similar to that of the wild type gland although the in vitro production of juvenile hormone by the former is much lower than that of the wild type gland. The ultrastructural features of the adult corpus allatum ofap ⁴ homozygotes reveal precocious degeneration and support the view that this non-vitellogenic mutant is a juvenile hormone deficient mutation.     

Ultrastructure of the corpus cardiacum and corpus allatum of the house cricket Acheta domesticus

Summary The ultrastructure of the corpus cardiacum (CC) and corpus allatum (CA) of the house cricket, Acheta domesticus, is described. Axon profiles within the CC contain neurosecretory granules 160–350 nm in diameter which are indistinguishable from those found in type I neurosecretory cells of the pars intercerebralis and in the nervus corporis cardiaci I. The CC itself contains two cell types: intrinsic neurosecretory cells and glial cells. Intrinsic NSC cytoplasm contains Golgi bodies and electron dense neurosecretory granules 160–350 nm in diameter. Synaptoid configurations with 20–50 nm diameter electron lucent vesicles were observed within axon profiles of the CC. The structure of the CA is relatively uniform with one cell type predominating. Typical CA cells possess large nucleoli, active Golgi complexes, numerous mitochondria, and occassional microtubules. Groups of dark staining cells scattered throughout the CA of some animals were interpreted as evidence of cellular death.This work was done while JTB was supported by USPHS Training Grant HD-0266 from NICHDI wish to express my thanks to Dr. Richard A. Cloney for sharing his expertise in electron microscopy     

Colony composition,queen behavior,specialized predation on millipedes,and exocrine glands in the ponerine ant Myopias conicara Xu, 1998 (Hymenoptera: Formicidae)

We collected a queenright colony of the very rare Myopias conicara Xu in Vietnam (1 dealate queen, 41 workers and 38 larvae). Both the queen and workers fed on xystodesmid millipedes. After paralyzing a millipede, its head was first removed by the workers, and then the larvae were put on the opening of the collum (anteriormost ring of the trunk). After the inner tissue of the collum was consumed, the exoskeleton of the collum was discarded. The feeding sequence was then repeated on the following rings of the trunk, until the entire prey was consumed. The ring‐shaped exoskeletons of the prey were deposited next to the nest entrance. The exocrine system of the workers (excluding the legs) contains 15 glands of which the structural features are similar to these of other ponerine ants. The presence of an oblong plate gland is interesting, as this gland had only been found previously in Myopias hollandi (Forel). However, none of the novel thoracic glands that were recently described in M. hollandi occur in M. conicara, which illustrates the variation within the genus Myopias. A unique characteristic of the class‐3 glands of Myopias ants is the gradual widening of the ducts, which has never been found in other insects, although the functional significance remains unknown.     

Labial gland disease in the genusFormica (Formicidae,Hymenoptera)

Summary Labial gland disease causes swelling of the labial glands in the pupal stage inFormica species. The resulting adults have enlarged thoraces and are called secretergates (Wasmann's pseudogynes). They infect the younger larvae, probably during feeding. The agent of the disease is unknown. It soon becomes non-infectious outside the labial glands. Diseased females were not seen to feed larvae. Yet their offspring contained secretergates. The discrepancy remains unexplained.     

Allatostatin-immunoreactive neurons projecting to the corpora allata of adult Diploptera punctata

Summary A monoclonal antibody against allatostatin I was used to demonstrate the allatostatin-immunoreactive pathways between the brain and the corpus cardiacum-corpus allatum complex in the adult cockroach Diploptera punctata. The antibody was two to three orders of magnitude more sensitive to allatostatin I than to the other four known members of the allatostatin family. Whole and sectioned brains in which immunoreactivity was localized with horseradish peroxidase-H₂O₂-diaminobenzidine reaction showed strongly immunoreactive cells in the pars lateralis of the brain with axons leading to and arborizing in the corpus cardiacum and the corpus allatum. Although many neurosecretory cells of the pars intercerebralis project to the corpora allata only, four strongly immunoreactive cells were evident here (two pairs on either side), and these did not project to the corpus cardiacum and corpus allatum but rather terminated within the protocerebrum in areas in which lateral cells also formed arborizations. Immunoreactivity was found in many other cells in the brain, especially in the tritocerebrum.     

Effects of gamma-radiation on the organisation of polytene chromosomes ofGlyptotendipes salinus Michailova (Chironomidae,Diptera)

A series of laboratory experiments onGlyptotendipes salinus were carried out in order to assess cytogenetic effects of different doses of gamma-radiation on polytene chromosomes, isolated from salivary glands. Chrinonomid larvae (III–IV larval stage) were irradiated with doses varying from 0.05 to 1.00 Gy (5–100 rad) and were bred under laboratory conditions until the fourth larval stage. Cytogenetic slides were analyzed for an estimation of occurrence of changes in the organization of the polytene chromosomes caused by gamma-radiation. A specific heterochromatin effect was found in certain chromosomes of the investigated species after 1.00 Gy irradiation. Decondensation of the centromeric heterochromatin and increased functional activity of Balbiany ring 2 were observed in the fourth (G) chromosome. Regression of the nucleolus of the first (AB) chromosome was detected.     

Ontogeny of some endocrine cells of the digestive tract in sea bass (Dicentrarchus labrax): An immunocytochemical study

Serotonin- and ten peptide-immunoreactive (IR) cell types were identified in the digestive tract of sea bass (Dicentrarchus labrax L.) larvae of four morphofunctional phases ranging in age from hatching to 61 days. The sequence of appearance and location of endocrine cells during ontogenetic development of the larvae was determined. The differentiation of endocrine cells followed a distal-proximal gradient in the gut which paralleled the morphofunctional differentiation. Serotonin-IR cells were identified in the last portion of the digestive tract from phase I onwards and in the gastric region from phase III, before these regions were morphofunctionally differentiated; met-enkephalin-IR cells were identified from phase II onwards in both the differentiated rectum and the undifferentiated intestine; cholecystokinin (CCK)- and synthetic human gastrin-34-IR cells were located only in the intestine and first found in the undifferentiated intestine of phase II; human gastrin-17-, peptide YY (PYY)- and neuropeptide Y (NPY)-IR cells appeared in the intestine from phase II and in stomach in phase IV, when it showed gastric glands; pancreatic polypeptide (PP)- and glucagon-IR cells were observed in both intestine and stomach, but insulin- and somatostatin-IR cells only in stomach, from phase III, during which the intestine but not the stomach was differentiated. PP- and PYY-, PP- and glucagon-, and PYY- and glucagon-like immunoreactivities coexisted from their first appearance in some cells of the gut.     

Four different head shapes in Daphnia hyalina (Leydig) induced by the presence of larvae of Chaoborus flavicans (Meigen)

In many species of Daphnia spines, neck teeth, and enlarged or reshaped helmets are well-known as defences against invertebrate predators. Until now, Daphnia hyalina (Leydig, 1860), a common species in many European lakes, has appeared to be an exception to this rule.Here, we provide evidence that the larvae of Chaoborus flavicans (Meigen) also can induce morphological changes in D. hyalina. Specimens react morphologically to the presence of larvae in three ways: (a) by changes in the shape of head shield, (b) by the formation of spine(s) on the head, and (c) by the elongation of the tail spine. The frequency and intensity of these morphological changes are correlated positively with midge larvae densities. The most pronounced reactions occurred in young D. hyalina.The predator kairomone also induced changes in Daphnia body size.     

Immunocytochemical studies on the naupliar nervous system of Balanus improvisus (Crustacea, Cirripedia, Thecostraca)

The nervous system of nauplii of the crustacean taxon Cirripedia was analysed in the species Balanus improvisus Darwin, 1854 using for the first time immunocytochemical staining against serotonin, RFamide and α-tubulin in combination with confocal laser scanning microscopy. This approach revealed a circumoesophageal neuropil ring with nerves extending to the first and second antennae and to the mandibles, all features typical for Crustacea. In addition, RFamidergic structures are present in the region of the thoraco-abdomen. A pair of posterior nerves and a pair of lateral nerves run in anterior-posterior direction and are connected by a thoracic nerve ring and a more posteriorly situated commissure. A median nerve is situated along the ventral side of the thoraco-abdomen. The innervation of frontolateral horns and the frontal filaments are α-tubulin-positive. Several pairs of large neurons in the protocerebrum, along the circumoesophageal connectives and in the mandibular ganglion stain only for serotonin. Due to the almost complete absence of comparable data on the neuroanatomy of early (naupliar) stages in other Crustacea, we include immunocytochemical data on the larvae of the branchiopod, Artemia franciscana Kellogg, 1906 in our analysis. We describe several characteristic neurons in the brains of the nauplius larvae of both species which are also found in decapod larvae and in adult brains of other crustaceans. Furthermore, our data reveal that the naupliar brain of cirripedes is more complex than the adult brain. It is concluded that this ontogenetic brain reduction is related to the sessile life style of adult Cirripedia.     

Puffing activity in the salivary gland chromosomes of Rhynchosciara under experimental conditions

By using the techniques of ligation of the larvae (brain and endocrine glands extirpation) and salivary gland implantation, the hormonal dependence of the activity of certain puffs of Rhynchosciara was investigated. Our results have shown that the puffing behaviour — activation and deactivation — varies according to the developmental stage in which the larvae were ligated. When the larvae were ligated just before the drastic changes in the puffing pattern, which occur prior to pupation, these changes fail to occur. When the larvae were ligated after the onset of these changes we have observed: a) some of the puffs active at the time of the ligature regress promptly, earlier than their normal timing observed in controls; b) others remain active indefinitely and c) there are still some which regress accordingly to the normal timing.The puff B2 which behaves as those in b was double checked by means of implantation experiments. Salivary glands which had puff B2 at its maximum expansion were implanted into younger larvae and that puff also remained active in the body cavity of these larvae. Hypotheses to explain the results obtained are discussed.     

Effect of habitat complexity on biological control by the red imported fire ant (Hymenoptera: Formicidae) in collards

A potentially important and understudied biological control agent in US agroecosystems is the red imported fire ant, Solenopsis invicta Buren. Red imported fire ants may be particularly important biological control agents because we can manipulate their abundance with changes in habitat complexity. The effect of habitat complexity on biological control by fire ants was determined using plots of collards intercropped with white clover (complex habitat) and simple collard monocrops. The most economically significant pests of collards are larvae of the diamondback moth (DBM), Plutella xylostella (L.). Predation of DBM larvae by fire ants was more rapid and efficient in the intercrop than the monocrop. Red imported fire ants were 23% less abundant in the intercrop than the monocrop, however, suggesting that fire ants had a greater per capita effect on DBM survival in the complex habitat. Red imported fire ant predation of DBM larvae was significantly affected by larval density. Red imported fire ants also reduced the survival of leaf beetles, another economically significant pest taxa, by 45%. Furthermore, collard leaf damage tended to be inversely related to fire ant density and fire ants were more effective at reducing crop damage in the complex intercrop. Our study indicates the ability of red imported fire ants to be effective biological control agents and suggests that increasing habitat complexity can enhance red imported fire ant efficacy and herbivore control.     

Observations onltl (lethal tumorous larvae) ofDrosophila melanogaster

A line ofGardner's tumorous head stock ofDrosophila melanogaster which is known to contain the inversion In (3L) Payne at varying frequencies, was found to be homozygous for another inversion, probably In (2L)t. The Payne inversion in this line is lethal when homozygous, and is balanced over a recessive lethal gene for which the symbolltl (lethal tumorous larvae) is proposed.ltl is located to the left ofRoughened on the basis of preliminary crossover tests.Homozygousltl larvae fail to pupate. They survive in the larval state for several days after pupation age. They exhibit a characteristic syndrome of abnormalities, part of which develops gradually during post-pupation age. Typical features of this syndrome are: over-abundance of blood cells, disintegration of fat-body, salivary gland, and parts of the gut, and the presence of brown or black masses (tumours). The absolute number of blood cells, and the proportion of different types of blood cells, further, the histolytic changes, in over-agedltl larvae are suggestive of changes which in normal development take place during metamorphosis. A striking feature ofltl are the melanotic pseudo-tumours. These usually float in the haemolymph; sometimes they are associated with organs. Tumour incidence is strongly influenced by genetic modifiers.A bacterial infection was found inltl. The infection is the consequence, rather than the cause, of some degenerative changes.The polytene chromosomes in salivary glands, Malpighian tubules, and parts of the gut ofltl larvae show striking abnormalities in their structure. They are shortened and thickened, and in advanced stages may assume a heterochromatine-like aspect through disintegration of the banding pattern. The changes resemble those found in conjunction with microbial infection inRhynchosciara andChironomus. In maleltl larvae the single X chromosome (in contrast to th double X in females) shows heterocyclic behaviour in that it is much shorter, wider, and fuzzier than the autosomes.Some aspects of the complex pleiotropic pattern of pathological changes inltl are discussed. Most abnormalities, including those of the chromosomes, are seen as an indirect effect, depending on physiological conditions in over-aged larvae. This is supported by observations on over-aged larvae of certain mutant types, or following treatment with 5-fluorouracil, which show similar chromosome changes. Several arguments support the view, thatltl larvae fail to pupate because of malfunction of the ring gland. Inability of the hypoderm to react is, however, not excluded as a possible explanation. Results of some transplantation experiments are included in the discussion. They show thatltl imaginal disks are capable of developing into adult organs.     

Sex-specific developmental profiles of juvenile hormone synthesis in honey bee larvae

Summary Juvenile hormone synthesis in drone larvae of the honey bee was measured by an in vitro radiochemical assay. The developmental profile of corpora allata activity in male larvae showed considerable differences from queen larvae, the presumptive reproductive females, and was comparable to workers, the sterile female morph. Drone and worker larvae, however, differed drastically in the regulation of juvenile hormone biosynthesis, as revealed by the addition of farnesoic acid to the culture medium. This precursor stimulated juvenile hormone synthesis of drone glands nearly eightfold, whereas in worker larvae it is known to lead to an accumulation of methyl farnesoate. The sex-specific differences in endocrine activity indicate a role for juvenile hormone in the expression of genetically determined sexually dimorphic characters during metamorphosis, a role not currently accounted for in models describing endocrine regulation of insect development. Correspondence to: K. Hartfelder     

An experimental study of population regulation in the salamander,Notophthalmus viridescens dorsalis (Urodela: Salamandridae)

Summary The roles of density-dependent larval survival and cannibalism of larvae as potential mechanisms of population regulation in the newt (Notophthalmus viridescens dorsalis) were evaluated in laboratory and field experiments. In laboratory containers, adults cannibalized larvae and large larvae cannibalized smaller larvae. In artificial ponds, larval survival did not depend on initial larval density. No cannibalism could be demonstrated in the complex environment, although the experiment was powerful enough to detect an ecologically relevant difference in survival. Adult growth was negatively correlated with the final biomass of larval newts, suggesting that the two life stages competed for resources. Larval growth rates were negatively correlated with final larval density, suggesting that larvae competed with each other. The proportion of larvae that became sexually mature at age 7 months (paedomorphs and adults that skipped the eft stage) varied inversely with larval density. Therefore, the potential regulatory mechanisms identified in this study are competition within and between life stages.     

Effects of ligation on ethanol-induced Balbiani ring puffing in salivary glands of Chironomus

Treatment of Chironomus larvae with dilute (0.5%–1.0%) ethanol results in puffing changes similar to those obtained with galactose in the Balbiani rings (BRs) of the salivary gland chromosomes. A shift in the relative size of BR1 and BR2 in chromosome 4 of C. pallidivittatus or C. tentans was observed within 1–2 days after ethanol treatment. The exceptional Balbiani ring, BR6 in chromosome 3, began to appear within 1 day after ethanol treatment of C. pallidivittatus and was fully developed after 3–4 days. Prepupae appeared to be refractory to the treatment. To localize possible controls of BR puffing in Chironomus, ligatures were made at various positions along the thorax and the anterior abdominal segments of the ethanoltreated larvae. In surviving larvae, ligated anterior to the brain or posterior to the salivary glands, induction of BR6 could be detected. In contrast, little or no BR6 puff induction was found in animals ligated in the middle of the second segment approximately between the brain and the salivary glands. No shift in the BR1/BR2 relation occurred with any of the ligations combined with ethanol treatment.     

Histology of the hormone-producing glands in the damp-wood termite <Emphasis Type="Italic">Hodotermopsis sjostedti</Emphasis> (Isoptera,Termopsidae): A focus on soldier differentiation

Caste differentiation in termites depends on complex hormonal changes during postembryonic development. Juvenile hormone (JH) is a central player in this process. The present study examined histological changes in the main hormone-producing endocrine glands, the corpora allata and molt glands, in the Japanese dampwood termite Hodotermopsis sjostedti. We focused on the soldier caste differentiation pathway, which can be induced artificially using an analogue of JH. The corpora allata exhibited volumetric changes during soldier induction, reflecting variations in the quantity of cytoplasm. Corpora allata from alates and neotenics clearly showed differentiation accompanied by cell proliferation, preparing for the high-level JH production necessary for reproduction. However, the volume increase of corpora allata was not always correlated to high JH titers. In contrast, molt glands degenerated in the reproductive castes. The JH analogue induced hypertrophy of the molt glands, along with the formation of lacunae, possibly related to ecdysteroid production. The JH analogue effect, inducing soldier differentiation, was suggested to require both mimic of high JH titers and stimulation of the molt glands. Received 12 November 2007; revised 2 June 2008; accepted 14 July 2008.     

Developmental regulation of juvenile hormone biosynthesis by the ring gland ofDrosophila melanogaster

Summary The synthesis in vitro of the putative dipteran juvenile hormone (JHB₃) by ring glands isolated from third instarDrosophila melanogaster larvae was quantified by a radiochemical assay. The data indicate that JHB₃ synthesis is developmentally regulated during the period prior to wandering until after puparium formation. The highest level of basal production occurred during the postfeeding stage, and synthesis declined after pupariation. Similar relative profiles of synthesis were obtained upon the addition of the JHB₃ precursor, farnesoic acid, although the absolute levels of production were elevated considerably. Basal JHB₃ production by brain-ring gland complexes in vitro was also highest during the postfeeding stage, although the synthetic rates were much lower than displayed by isolated ring glands. Further analysis revealed that methyl farnesoate, a JHB₃ precursor, was synthesized by brain-ring gland complexes in significant quantity. A dual mechanism of brain-centered control of JHB₃ biosynthesis is proposed.To whom offprint requests should be sent     

Comparative ultrastructure of coxal glands in unfed larvae of Leptotrombidium orientale (Schluger, 1948) (Trombiculidae) and Hydryphantes ruber (de Geer, 1778) (Hydryphantidae)

Coxal glands of unfed larvae Leptotrombidium orientale (Schluger, 1948) (Trombiculidae), a terrestrial mite parasitizing vertebrates, and Hydryphantes ruber (de Geer, 1778) (Hydryphantidae), a water mite parasitizing insects were studied using transmission electron microscopy. In both species, the coxal glands are represented by a paired tubular organ extending on the sides of the brain from the mouthparts to the frontal midgut wall and are formed of the cells arranged around the central lumen. As in other Parasitengona, the coxal glands are devoid of a proximal sacculus. The excretory duct, joining with ducts of the prosomal salivary glands constitutes the common podocephalic duct, opening into the subcheliceral space. The coxal glands of L. orientale are composed of a distal tubule with a basal labyrinth, an intermediate segment without labyrinth, and a proximal tubule bearing tight microvilli on the apical cell surface and coiled around the intermediate segment. The coxal glands of H. ruber mainly consist of the uniformly organized proximal tubule with apical microvilli of the cells lacking the basal labyrinth. This tubule shows several loops running backward and forward in a vertical plane on the side of the brain. In contrast to L. orientale , larvae of H. ruber reveal a terminal cuticular sac/bladder for accumulation of secreted fluids. Organization of the coxal glands depends on the ecological conditions of mites. Larvae of terrestrial L. orientale possess distal tubule functioning in re‐absorption of ions and water. Conversely, water mite larvae H. ruber need to evacuate of the water excess, so the filtrating proximal tubule is prominent.     

Structure and development of bracteal nectary glands in Aphelandra (Acanthaceae)

A survey of bracteal (extrafloral) nectaries in species of Aphelandra (Acanthaceae) reveals substantial diversity. Each bracteal nectary is an aggregate of individual glands that vary in number, size, and structure among species. Glands contain three cell layers: a palisade-like secretory cell layer, a one-to-many-celled intermediate layer with thickened cell walls, and a foot layer. Members of the A. pulcherrima complex have one of two distinct gland types: relatively small glands with a single-celled intermediate layer or larger glands that have a multicellular intermediate layer. Nectaries composed of small glands are patches of many (>50) glands, whereas those composed of large glands are patches of < 10 glands. Four outgroup species have bracteal nectaries of numerous small glands with pluricellular intermediate layers. Glands of all three types are initiated as single enlarged protodermal cells, and all undergo similar early periclinal divisions; the large-gland type shows greater subsequent enlargement with many more anticlinal divisions. The bracteal nectar glands are interpreted to be homologous with simpler glandular trichomes, and mark a monophyletic lineage within Aphelandra. Comparisons with outgroup species show that both nectary types in the A. pulcherrima complex have diverged from an ancestral condition of numerous small glands with pluricellular intermediate layers. Use of the ontogenetic criterion to polarize gland type within the A. pulcherrima complex would yield erroneous results because evolution has apparently involved a developmental truncation with loss of cell divisions in the intermediate layer of small glands. Comparable nectar glands in more distant taxa are interpreted as remarkable cases of convergent evolution, perhaps from similar trichome precursors.