Ultrastructure of differentiating hemocytes in the embryo of Oncopeltus fasciatus Dallas (Insecta,Heteroptera)

Summary The hemocytes of Oncopeltus differentiate rather early during embryogenesis. They are segregated by the mesoderm soon after its formation (about 50h after egg deposition). Newly segregated hemocytes show the typical features of embryonic cells: many free ribosomes, a few strands of rough ER, the cisternae of which are considerably distended, electron lucent vacuoles around the periphery, and glycogen deposits. A few hours thereafter the hemocytes undergo striking subcellular changes. First, glycogen, electron lucent vacuoles and rough ER disappear and phagocytotic activity can be observed. Golgi complexes become well expressed and give rise to electron dense vesicles which fuse to larger bodies. Then, rough ER develops again and occupies large areas of the cytoplasm. Its cisternae are often considerably distended by proteinaceous secretions. All hemocytes undergo the same steps of differentiation.Embryonic hemocytes obviously play a decisive role in the elimination of waste products, in particular of tissue debris that results from programmed cellular death. The significance of the conspicuous protein secretions is not fully understood. They may participate in the deposition of the acellular connective tissue, or may have some of the other functions ascribed to insect blood cells.Larvae and imagines of Oncopeltus have four types of hemocytes, which agree rather well with those found in Rhodnius (Lai-Fook, 1970). All embryonic hemocytes, aside from the newly segregated ones, represent plasmatocytes but, unlike plasmatocytes of postembryonic stages, they contain no large inclusion bodies. Newly segregated embryonic hemocytes, in addition to their typical embryonic features, have some similarities with larval and adult prohemocytes. Oenocytoids and granulocytophagous cells are absent in the embryo. Some aspects concerning the differentiation and classification of hemocytes are discussed.Supported by research grant Do 163 from the Deutsche ForschungsgemeinschaftThe author is grateful to Ms. K. Schmidtke and Ms. M. Ullmann for technical assistance     

Feinstruktur eines maxillaren Muskelrezeptors bei Oncopeltus fasciatus (Insecta,Heteroptera)

Zusammenfassung Im Kopf von Oncopeltus fasciatus wird erstmals für Insekten ein maxillarer nicht-ciliärer Muskelrezeptor in seiner Feinstruktur beschrieben. Er ist zwischen dem Hypopharynx-Flügel und dem Maxillen-Hebel aufgespannt und wird dementsprechend bei der Protraktion der Maxille gedehnt. Der reizübermittelnde Teil ist zusammengesetzt aus zwei caudal gelegenen, sehr dünnen Muskelfasern und einem Bindegewebs-Strang im vorderen Drittel. Die beiden Fasern des Rezeptor-Muskels bilden in ihrem vorderen Bereich eine Röhre. Die motorische Innervierung der Fasern geschieht vom Lumen der Röhre her. Fünf Sinneszellen senden ihre Dendriten zum Bindegewebs-Strang, wo sie zwischen den Fibrillen enden. Der beschriebene Maxillen-Rezeptor ist möglicherweise serial-homolog dem dorsalen Mandibel-Rezeptor anderer Insekten.

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Fine structure of a maxillary muscle receptor in Oncopeltus fasciatus (Insecta, Heteroptera)

Summary The fine structure of a non-ciliary muscle receptor in the maxilla of Oncopeltus fasciatus is described. The receptor extends anteriorly from its origin at the hypopharyngeal wing to its insertion at the maxillary lever. Accordingly it is stretched during protraction of the maxilla. The stimulus-transmitting part consists of two very thin, caudally situated muscle fibres and a connective tissue strand situated in the cranial third. The receptor muscle fibres form a tube in their cranial part. They are innervated by a motor axon lying in the lumen of the tube. Five sensory cells send their dendrites to the connective tissue strand, where they end among the filaments. The maxillary receptor described here is possibly an organ serially homologous to the dorsal mandibular muscle receptor of other insects.

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Mit Unterstützung durch die Deutsche Forschungsgemeinschaft     

Ultrastructure of embryonic envelopes and integument ofOncopeltus fasciatus dallas (Insecta,Heteroptera)

Summary The embryo ofOncopeltus fasciatus forms a typical secondary dorsal organ (SDO). It develops after katatrepsis from the contracting serosa, the cells of which decrease in diameter but increase considerably in height. After 66 h, the SDO represents a protrusion of the serosal epithelium above the head and is then reduced to a disc-shaped formation, which sinks into the yolk, where it disintegrates after 80 h.During its typical expression, between 66 and 78 h, the SDO shows a zonal arrangement of its cell organelles. The nucleus, which is located in the basal cell region, has a very irregular outline and includes several nucleoli and globular inclusion bodies. Rough and smooth ER are well developed around the nucleus and suggest the involvement of the organ in protein secretion as well as in lipid metabolism. Electron-lucent vacuoles and electron-dense granules, sometimes enclosed in the vacuoles, accumulate in the apical cell region, and are obviously extruded into the peripheral (extraembryonic) space. The formation of intercellular clefts and delicate cytoplasmic extensions facing the yolk and microvilli facing the periphery evidence a transporting function of the epithelium. Blisters intercalated in extended junctional complexes between apical cell regions point to the transport of solutes.Because of the similarities of the processes observed in the SDO and in Malpighian tubules of larvae, an excretory function of the SDO is suggested. Final products of yolk and embryo are apparently transported to the extraembryonic space, where they accumulate during embryogenesis.Phylogeny, relationship, and function of the different embryonic glands in Arthropoda (primary and secondary DO and pleuropodia) are discussed.Dedicated to Prof. Dr. B. Scharrer on the occasion of her birthdaySupported by the Deutsche ForschungsgemeinschaftI am grateful to Miss K. Schmidtke and Mrs. M. Ullmann for technical assistance     

Saugverhalten und Nahrungsaufnahme von Oncopeltus fasciatus Dallas (Heteroptera,Lygaeidae)

Zusammenfassung Das Verhalten von Oncopeltus fasciatus bei der Nahrungssuche und- aufnahme wurde untersucht. Durch Aufspeicheln und Aufsaugen von Speichelsekret wird ein Substrat auf Eignung für Einstich und Nahrungsaufnahme geprüft. Die histologische Bearbeitung des Saugortes in einer Pflanze (Vicia faba) zeigt eine deutliche Bevorzugung des Leitungssystems beim Einstich. Hier werden Speichelscheiden gebildet. Im Samen (Asclepias syriaca und Helianthus annuus) werden die reservestoffreichen Cotyledonen besaugt. Der Einstich erfolgt ohne Sekretion einer Speichelscheide. Die Funktion dieser Speichelscheide wird diskutiert. Unter extremen Bedingungen tritt bei der sonst phytophagen Wanze trotz ihres ausgeprägten Subsozialverhaltens Kannibalismus auf. Beim Durchstechen der Cuticula dürften überwiegend mechanische Kräfte wirksam sein. Im Speichel konnte kein Chitin-spaltendes Enzym nachgewiesen werden. Weiterhin wurde die Saugzeitenverteilung zwischen Pflanze (Wasseraufnahme) und Samen (Nahrungsaufnahme) über einen Tagesablauf bestimmt. Die Wanzen dürften an der Pflanze in kürzeren Saugphasen Sättigung erreichen als an den dehydratisierten Samen. Die beträchtliche Menge and Speichel (1,14 mg/Wanze/Std), die in einen Samen injiziert werden, emulgieren und suspendieren dessen Inhalt und bringen ihn so in eine für das Insekt aufsaugbare Form.

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Summary The feeding behaviour of Oncopeltus fasciatus has been investigated. Exploration of food materials is performed by means of watery saliva which is secreted onto surfaces of substrates and sucked back again. Histological tests indicate that the animal preferably pierces the conducting system of the Vicia faba plant. Oncopeltus fasciatus secretes sheath material which coagulates and forms a lining to the path of the stylets during plant feeding. Feeding on seeds (Asclepias syriaca and Helianthus annuus) is not accompanied by stylet sheath formation. The function of this stylet sheath is discussed. Under extreme conditions the phytophagous animal shows cannibalism in spite of its marked subsocial behaviour. Penetration of the cuticle seems to be effected mainly by mechanical forces. No chitin-splitting enzyme could be detected in the saliva. The feeding activity over a photoperiod of 12 hrs on plants (uptake of water) and seeds (uptake of nutritive materials) is determined. It is suggested that on a green plant the animal is saturated more rapidly than on dehydrated seeds. The considerable amounts of watery saliva emulsify and suspend the contents of the seeds. Into seeds of Asclepias syriaca saliva is injected at a rate of approximately 1.14 mg/animal/hr.

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Durchgeführt mit Unterstützung der Deutschen Forschungsgemeinschaft im Rahmen einer Herrn Prof. Kloft gewährten Sachbeihilfe.     

Ultrastructural Analysis of the Neuroendocrine Apparatus of Oncopeltus fasciatus (Heteroptera)

• 1 In Oncopeltus fasciatus, the A-cells of the pars intercerebralis and their tracts are stainable in situ with the performic acid-victoria blue (PAVB) method. The axons from these cells, after traversing the corpus cardiacum, terminate in the anterior part of the aorta which thus serves as the neurohemal organ.
• 2 Ultrastructurally, four types of secretory neurons are distinguishable in the pars intercerebralis region: pic-I with granules measuring 1000–3000 Å in diameter; pic-II with granules of irregular size and shape, the elongate ones showing mean dimensions of 2400 × 1400 Å; pic-III with less electron-dense granules measuring 1000–2700 Å in diameter; pic-IV, present not only in the pars intercerebralis but also in adjacent regions of the brain, with variable proportions of granules measuring 700–1800 A and dense-cored vesicles measuring 1000–2400 Å.
• 3 The nervi corporis cardiaci contain at least three types of neurosecretory axons, based on granule content, presumably representing pic-I, pic-II and pic-III neurons.
• 4 The wall of the aorta contains endings of at least three distinct types, again representing pic-I, pic-II and pic-III neurons, and thus provides the neurohemal site for these three types of protocerebral neurosecretory cells. Axons of pic-IV neurons appear to enter the cerebral neuropil.
• 5 The corpus cardiacum is composed of two types of parenchymal secretory cells, with electron-dense granules measuring 1300–3000 Å and 1000–2300 Å in diameter, respectively. The corpus cardiacum also contains interstitial cells and some axons of extrinsic origin, with and without granules.
• 6 The corpus allatum may be paired or median, and receives a small number of at least two types of axons. The corpora allata of some reproducing females show a large number of PAVB-stainable inclusions which appear to be modified cytoplasmic organelles, but are definitely not neurosecretory material.
• 7 The hypocerebral ganglion is composed of two types of secretory-appearing neurons and glial cells. The two neuronal types contain secretory granules, 1000–3000 Å and 900–2100 Å in diameter, respectively. Axons of the recurrent nerve also may contain occasional granules.
• 8 In this heteropteran insect, the two principal functions of the corpus cardiacum appear to be spatially separated: the neurohemal function is subserved by the aortic wall, which permits release of material into both the aortic lumen and the hemocoel, and the intrinsic endocrine function is possessed by the parenchymal cells.

     

Cadmium effects on development and reproduction of Oncopeltus fasciatus (Heteroptera: Lygaeidae)

Newly hatched nymphs of the insect Oncopeltus fasciatus were exposed to various concentrations of CdCl2 administered in drinking water until the end of adult life. Significant nymphal mortalities were observed at concentrations above 30 mg Cd/l (corresponding to the LC50). The duration of the nymphal stages increased in proportion to the Cd concentration; at the lowest Cd concentration of 10 mg Cd/l, the median duration was significantly prolonged by one day, while at the highest concentration of 100 mg Cd/l it was increased by 10 days over the control group. The weight of newly emerged adults lineally decreased with Cd concentration, being reduced to half the weight of controls at 100 mg Cd/l. In addition, a proportionality between delay in development and weight reduction was found in Cd-treated adults. Survival of adult females was decreased at concentrations higher than 10 mg Cd/l, while males were only affected at 30 mg Cd/l or higher doses. Reproduction was the most affected parameter. Oviposition rate, fecundity and fertility of females exposed to 10 mg Cd/l were significantly lower than controls (73%, 58% and 55% relative to controls, respectively). Hatchability of the eggs laid by treated females was also reduced. These results show that development and reproduction of O. fasciatus are seriously impaired at sublethal Cd concentrations.     

Vitellogenesis inhibition in Oncopeltus fasciatus females (Heteroptera: Lygaeidae) exposed to cadmium

Newly moulted females of the insect Oncopeltus fasciatus were exposed to cadmium (Cd) dissolved in the drinking water (50-400 mg l(-1) Cd) for 5 days. Cd exposure delayed ovarian maturation and inhibited egg production. Exposure to Cd, moreover, decreased hemolymph levels of the two major vitellogenin polypeptides of O. fasciatus, VG1 and VG2, in a concentration-dependent way, probably by a reduction in their synthesis. The ovarian levels of VG1 and VG2 were also decreased in Cd-exposed females. It was next investigated whether Cd effects might be a consequence of the endocrine disruption of vitellogenin synthesis, which is controlled by juvenile hormone (JH). JH replacement therapy did not restore VG1 or VG2 levels in Cd-exposed females, but did so in starved females. Our results do not therefore support a disturbance of JH production or a reduction in feeding as the cause of the reduced vitellogenin polypeptide levels, but rather point to the site of action of JH, the JH receptor, as the target of Cd effects.     

Pharmacological observations on body fluids from the milkweed bug,Oncopeltus fasciatus (Dallas) (Heteroptera: Lygaeidae)

A report is given on the pharmacological activity of body fluids from milkweed bugs maintained on a diet of sunflower seeds, together with observations on the toxin accumulating system of the adult insect.     

Detoxifying enzymes and the effects of temperature on the toxicity of malathion to Oncopeltus fasciatus (Heteroptera) and Tenebrio molitor (Coleoptera)

1. The effects of ambient temperature (T_a) on the toxicity of malathion to various life cycle stages of Tenebrio molitor and Oncopeltus fasciatus were investigated.2. Higher T_a (35°C) had a significant effect on toxicity, especially at concentrations above 70ppm. Nymphal stages of O. fasciatus were more susceptible than adults. The pupal stage of T. molitor was most resistant to combinations of high T_a and insecticide concentration.3. ld₅₀ ranged from 0.11 μg/insect to 0.23 (T. molitor), and 0.11 to 0.17 (O. fasciatus).4. Activity (μmol/min/mg protein) of carboxylesterase and glutathione S-transferase ranged from 0.72–1.97, and 0.47 to 1.35, respectively.     

The mandibular muscle receptor organ of Homarus gammarus (L.) (crustacea,decapoda)

Summary A muscle receptor organ is present in the mandible of macruran decapods. The mandibular muscle receptor organ (Mand. MRO) of Homarus gammarus (L.) consists of a ribbon of muscle innervated at its ventral insertion by 10–20 multiterminal sensory neurones. The sensory cells have a small number of dendritic processes.The receptor muscle exhibits some structural properties of both fast and slow muscle. The mean sarcomere length is similar to that of the slow abdominal MRO but the receptor muscle in cross section has a punctate distribution of myofibril bundles more typical of fast muscle.This work was supported by Science Research Council grants B/SR/1871 and BR/G/585.     

Sensory activity of the mandibular muscle receptor organ of Homarus gammarus (L)

The mandibular muscle receptor organ (Mand. M.R.O.) of Homarus gammarus (L) exhibits increased activity to receptor muscle (R.M.) contraction (decrease in length) and to stretch (increase in length).

The sensory units of this receptor differ in their threshold to R.M. tension and in the frequency change they exhibit for a given increment in tension. The units fire tonically during maintained tension once their threshold has been reached.

Both the number of active units and their frequency increase with R.M. tension. The Mand. M.R.O. is velocity sensitive and exhibits a higher degree of activity during rapid stretch. This dynamic response increases with rate of R.M. stretch.

The activity of the Mand. M.R.O. sensory neurones is compared with that of other M.R.O.’s and the authenticity of some aberrant units is discussed.     

Documentation of brochosomes within Hemiptera, with emphasis on Heteroptera (Insecta)

Brochosomes, small secretory particles often found in abundance on the integument of leafhoppers, are currently considered a unique feature of the family Cicadellidae. The present work documents, for the first time, brochosomes in two other groups of Hemiptera, i.e. Psylloidea and Heteroptera. In Heteroptera the occurrence of relatively large amounts of brochosomes on various body parts is documented in several species of different families. Morphological structures of the legs and the setation are illustrated in detail and compared to those of Cicadellidae. The results are based on scanning electron microscopy (SEM) examination of museum specimens. The possible function of brochosomes within Hemiptera is briefly discussed.     

Differential infectivity of two Pseudomonas species and the immune response in the milkweed bug, Oncopeltus fasciatus (Insecta: Hemiptera).

Pseudomonas aeruginosa and Pseudomonas putida show a profound differential infectivity after inoculation in Oncopeltus fasciatus. Whereas P. putida has no significant impact on nymphs, P. aeruginosa kills all experimental animals within 48 h. Both Pseudomonas species, however, induce the same four hemolymph peptides in O. fasciatus. Also injection of saline solution and injury induced these peptides. In general peptide induction was stronger in nymphs than in adult males. A significantly higher number of nymphs survived a challenge with P. aeruginosa when an immunization with P. putida preceded. The antibacterial properties of the hemolymph were demonstrated in inhibition experiments with P. putida. Two of the four inducible peptides (peptides 1 and 4) could be partially sequenced after Edman degradation and were compared with known antibacterial peptides. Peptide 1, of 15 kDa, showed 47.1% identity with the glycine-rich hemiptericin of Pyrrhocoris apterus. Peptide 4, of 2 kDa, had a 77.8% identity with the proline-rich pyrrhocoricin of P. apterus and a 76.9% identity with metalnikowin 1 of Palomena prasina. Peptides 2 and 3 are also small, with molecular weights of 8 and 5 kDa.     

Numerical allometric growth of the ommatidia,antennal sensilla,and teeth of foretibial combs in the milkweed bug Oncopeltus fasciatus Dallas (Heteroptera : Lygaeidae)

Oncopeltus fasciatus (Heteroptera : Lygaeidae), the milkweed bug, was bred in captivity. Sampling showed that individuals grow exponentially through their 6 developmental stages with an average linear increase per molt of 42% for the females and 41% for the males. The number of ommatidia per eye grows with negative allometry from an average of 30 in the first instar to 860 in the male and 820 in the female adult. The total number of sensilla on the 2 flagellar segments of an antenna increases with negative allometry during the 5 nymphal stages from a mean of 239 in the first instar to 2462 in the last. At this point, this allometric growth pattern is sharply broken by distinct numerical increase to 7163 on the adult flagellum. The number of teeth composing the foretibial comb, the tool for grooming the distal flagellar segment, grows with negative allometry through all 6 developmental stages. Calculations using previously published data from the migratory locust, Locusta migratoria, revealed the same growth pattern of antennal sensilla: uniform allometric growth during the nymphal development, broken by a conspicuous upward jump to the adult number of sensilla. In the American cockroach, Periplaneta americana, this growth pattern of antennal sensilla holds only for the male; the female continues the nymphal allometric growth into the adult stage. These observations on allometric growth fit three theoretical explanations: 1. Smooth allometric growth is evidence for an aut-adaptation to increasing size. 2. Ex-adaptations to novel ecological niches cause breaks in allometric growth patterns. 3. Chapman's rule, which states that increased mobility correlates with greater olfactory sensitivity, correctly predicts the observed breaks in the allometric growth patterns in the abundance of antennal sensilla.