Carbohydrases in the alimentary canal of the large milkweed bug, Oncopeltus fasciatus (Hemiptera: Lygaeidae)

Adults of the large milkweed bug, oncopeltus fasciatus (Dallas), deprived of food for 48 hr, were fed 5% solutions of either sucrose, maltose, lactose, raffinose or melezitose, for 15–20 min. The alimentary canals were then dissected out 30 min or 1 hour after the period of feeding, and the gut contents chromatographed. The results indicated the presence in the gut of the following carbohydrases: -glucosidase, -fructosidase, -galactosidase and -galactosidase.

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Résumé Des adultes de la punaise de l'asclépiade, Oncopeltus fasciatus (Dallas), soumis au jeûne pendant 48 heures, ont été nourris ensuite durant 15 à 20 minutes avec des solutions aqueuses de 5% de glucides, comprenant soit le sucrose le maltose, le lactose, le raffinose ou le mélézitose. Les tubes digestifs furent prélevés 30 ou 60 minutes après l'ingestion des sucres, et leur contenu glucidique séparé et identifié par chromatographie sur papier filtre. Les résultats ont révélé la présence dans le tube digestif des carbohydrases suivantes: -glucosidase, -fructosidase, -galactosidase et -galactosidase.

     

Responses of the large milkweed bug, Oncopeltus fasciatus (Hemiptera: Lygaeidae) to chemically defined diets

The large milkweed bug, Oncopeltus fasciatus (Dallas), was reared from fourth instar to the adult stage on chemically defined diets, and was maintained alive for 2 to 5 months on such diets. Insects grew better on diets containing 5% sucrose than on those containing 3, 10 or 20% sucrose, and gained almost as much weight as those on milkweed seed and water. Newly hatched nymphs gained almost ten times in weight and moulted once or twice on different diet solutions, but never reached the adult stage. Diluted diets greatly prolonged the length of the stadium and survival of first- and second-instar nymphs, but these did not reach the adult stage. Ommission of cholesterol from the diet had no effect either on growth or moulting of this insect.

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Résumé On a pu élever la punaise de l'asclépiade, Oncopeltus fasciatus (Dallas) sur des régimes de composition chimique définie, ceci à partir du quatrième stade larvaire jusqu'à l'imago, et la maintenir sur de tels régimes durant deux à cinq mois consécutifs. La croissance pondérale de l'insecte a été supérieure sur les régimes contenant 5% de sucrose que sur ceux contenant 3, 10 ou 20% de sucrose, et est comparblle à celle obtenue sur les régimes à base de graines d'asclépiade. La croissance des larves fra?chement écloses placées sur de tels régimes a été décuplée; ces larves ont mué une ou deux fois, sans toutefois atteindre le stade adulte. Des régimes dilués ont eu pour effet de prolonger considérablement la survie et la durée des larves de premier et deuxième stades. Labsence de cholestérol dans les régimes nutritifs a semblé n'avoir aucun effet sur la croissance et la mue.

     

乳草长蝽Ubx基因克隆及多转录本分析

针对非完全变态类昆虫发育关键基因的研究相对匮乏, 尤其缺少Hox基因家族的基因结构和序列信息。为了研究Hox基因家族成员之一的Ubx基因在非完全变态类昆虫中的结构特点, 本实验选取乳草长蝽Oncopeltus fasciatus (Dallas, 1852)为代表, 应用RACE和RT-PCR技术, 对其Ubx基因的全长开放阅读框进行克隆。结果显示: 乳草长蝽Ubx基因（Of-Ubx）开放阅读框全长888 bp, 推测的完整蛋白含有295个氨基酸。Southern blot证实Ubx基因以单拷贝形式存在且含有内含子。在Of-Ubx的YPWM基序和同源异型结构域之间存在选择性剪接位点, 可产生3种不同转录本。分析以上实验结果, 发现乳草长蝽与黑腹果蝇Drosophila melanogaster (Meigen, 1830)的Ubx基因拥有相似的剪接位置、剪接体组合和边界序列, 提示它们很可能具有相似的剪接机理。这是Ubx基因的多转录本现象在昆虫纲中果蝇属以外类群中的首次详尽报道。
     

Embryology of the thoracic and abdominal ganglia of the large milkweed bug, Oncopeltus fasciatus (Dallas), (Hemiptera, Lygaeidae)

In this study, the condensation of the three thoracic and 11 abdominal segmental ganglia to form a prothoracic and central nerve mass during embryogenesis is described. During katatrepsis, many changes occur in the organization of these ganglia; this study suggests that some of these changes are caused by mechanical forces acting on the ventral nerve cord at this time. The ventral nerve cord begins its anterior migration and coalescence ten hours after katatrepsis and is completed 63 hours later. The central ganglion is made up of the meso- and metathoracic ganglia and seven abdominal ganglia. Intrasegmental median cord nuclei are shown to form glial elements in the median sagittal plane of the neuropile and in the longitudinal connectives. Intersegmental median cord neuroblasts migrate into the posterior gangliomeres but, apparently, degenerate soon after katatrepsis. Lateral cord cells bordering on the neuropile form a glial investment that surrounds this fiber tract region. Peripheral lateral cord cells are shown to form the cells of the outer ganglionic sheath, the perineurium.     

Absence of ribosomal DNA amplification in the meroistic (telotrophic) ovary of the large milkweed bug Oncopeltus fasciatus (Dallas) (Hemiptera: Lygaeidae)

In the typical meroistic insect ovary, the oocyte nucleus synthesizes little if any RNA. Nurse cells or trophocytes actively synthesize ribosomes which are transported to and accumulated by the oocyte. In the telotrophic ovary a morphological separation exists, the nurse cells being localized at the apical end of each ovariole and communicating with the ooocytes via nutritive cords. In order to determine whether the genes coding for ribosomal RNA (rRNA) are amplified in the telotrophic ovary of the milkweed bug Oncopeltus fasciatus, the percentages of the genome coding for ribosomal RNA in somatic cells, spermatogenic cells, ovarian follicles, and nurse cells were compared. The oocytes and most of the nurse cells of O. fasciatus are uninucleolate. DNA hybridizing with ribosomal RNA is localized in a satellite DNA, the density of which is 1.712 g/cm(-3). The density of main-band DNA is 1.694 g/cm(-3). The ribosomal DNA satellite accounts for approximately 0.2% of the DNA in somatic and gametogenic tissues of both males and females. RNA-DNA hybridization analysis demonstrates that approximately 0.03% of the DNA in somatic tissues, testis, ovarian follicles, and isolated nurse cells hybridizes with ribosomal RNA. The fact that the percentage of DNA hybridizing with rRNA is the same in somatic and in male and female gametogenic tissues indicates that amplification of ribosomal DNA does not occur in nurse cells and that if it occurs in oocytes, it represents less than a 50-fold increase in ribosomal DNA. An increase in total genome DNA accounted by polyploidization appears to provide for increasing the amount of ribosomal DNA in the nurse cells.     

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.     

Regeneration of appendages in the large milkweed bug, Oncopeltus fasciatus

An analysis was made of the regeneration of legs and antennae of Oncopeltus. Amputations were performed on first instar larvae within 24 hr after hatching, and on later instars within 24 hr after ecdysis. The resulting regenerates were then measured at each instar. When amputations were performed soon after hatching, there was no significant effect on the duration of any instar. The regenerate was usually visible after the second post-operative ecdysis, and was smaller than a normal appendage (hypomorphic). Removal of the three distal segments of the antenna usually resulted in regeneration of only one segment which was abnormally long and showed a combination of the bristle patterns characteristic of the two most distal segments of the control. In a few such cases a partial intersegmental membrane was present in the regenerated segment. Removal of the tarsus resulted in a structurally complete regenerate which was smaller than the control tarsus. The largest leg regenerates were obtained when amputation was performed through the tibia. With amputation through the femur, a decrease in length of the remainder of this segment was observed after the first ecdysis. This type of amputation and amputation through the trochanter in some cases resulted in the formation of a globular stump containing tarsal claws. The results indicate that amputation of part of an appendage in Oncopeltus does not stimulate an increased growth rate in the stump, but merely causes reorganization of the stump material which subsequently grows at the normal rate. Since even the most hypomorphic regenerates contained well-formed claws, even though proximal parts were missing, it appears that the reorganization process must begin at the most distal point and proceed proximally.     

Natural food requirements of the large milkweed bug,Oncopeltus fasciatus (Hemiptera: Lygaeidae), and their relation to gregariousness and host plant morphology

Summary The life ofOncopeltus fasciatus centers on the seeds of milkweeds (Asclepiadaceae,Asclepias syriaca in this study). Adults reproduce prolifically on these seeds, but they engage in only half as much copulation and lay only a few eggs when fed milkweed buds and flowers instead. They can not maintain body weight on a diet of just vegetative plants. Vegetative shoots support only slow growth and produce adults only in certain circumstances.Seeds are often inaccessible to nymphs in the three youngest instars, since their mouthparts are too short to penetrate the thick walls ofA. syriaca pods. Nymphs feeding from the outside of closed pods develop more slowly than those feeding on exposed seeds. Since mortality occurs at a constant rate, slow growth results in fewer surviving. Even adults, which can feed through almost any pod wall, prefer to feed where it is thinnest. Thus the pod wall effectively protects many seeds from this herbivore.Nymphs in larger groups (20 individuals) suffer much lower mortality than those in small groups (5 individuals), when they are feeding from the outside of closed pods. However, group size does not affect survival when nymphs are fed seed. Gregariousness apparently partly compensates for the less nutritious diet attainable from the outside of pods and thus is related to this bug's extreme specialization of diet.Other characteristics coordinated with the seed requirement include the timing of migration and egg laying, the female's choice of oviposition site, and the nymphs' balanced tendencies to be sedentary and to disperse. Among the milkweeds, such traits as thick pod walls, wide spacing, and rapid seed dispersal could have been selected for by a seed predator such asO. fasciatus.As a specialist and a probable agent of such selection,O. fasciatus is committed to keeping up with changes in its host plant. This requires maintaining some flexibility in its behavior or gene pool. K. Evans (personal communication) finds thatO. fasciatus in California onA. fascicularis lays eggs so early that the first nymphs hatch as the first flowers are opening. In that more equitable climate and on that host, adult reproduction is apparently not as dependent on pods being present in the colonized patch, and the nymphs must rely on non-seed food more often than they do in the association withA. syriaca in the East and Midwest. This very specialized species apparently retains enough adaptability to exploit milkweeds of various forms and phenologies living in a wide range of climates. This adaptability could promise its continued success in the coevolutionary race with its host plants.     

Supernumerary regeneration in the large milkweed bug Oncopeltus fasciatus.

As an approach to the problem of pattern formation in the insect appendage, various graft combinations were studied in the legs of the large milkweed bug Oncopeltus fasciatus. Metathoracic legs of fourth instar larvae were amputated through the tibia within 24 hr after ecdysis and grafted back onto the stumps. The orientation of the graft was altered by rotation through 90 or 180° and/or by exchanging right and left stumps and grafts, yielding seven possible orientations in addition to the control. Many of these grafts resulted in the production of one or two supernumerary regenerates of the distal segments, which appeared at the graft junction after the second postoperative ecdysis. When two supernumerary regenerates resulted, one appeared to be produced from the stump and the other from the graft. When one regenerate was present, it appeared to be a composite of material produced from both the stump and the graft. In contrast to the results obtained in cockroaches, the external face of the leg appeared to be the only one capable of giving rise to a supernumerary regenerate.     

Intercalary leg regeneration in the large milkweed bug Oncopeltus fasciatus.

Grafting operations were performed on the metathoracic legs of fourth instar Oncopeltus fasciatus within 24 hr after ecdysis. Different levels along the tibia were combined so that a lengthened tibia, approximately 1.5 times the normal length, or a shortened tibia, about half the normal length, were created. Intercalary regeneration occurred between the graft and stump in both combinations and the extra tissue was visible on the adult leg. The intercalary regenerate produced by the lengthened tibia showed reversed bristle polarity, while that produced in the shortened segment showed normal polarity. It is suggested that a regenerate with reversed polarity represents a mirror image duplication of the graft and might originate from the graft, whereas a regenerate with normal polarity may originate, as in normal regeneration, from the stump. It appears that each level in the appendage has the developmental capacity to produce only more distal structures. This conclusion is supported by the results of a grafting operation in which a portion of the tibia was grafted back on to the stump with its proximo-distal axis reversed. Regeneration of appropriate distal structures proceeded from the free proximal surface of the grafted tibia.     

Identification of the adipokinetic hormone of the large milkweed bug Oncopeltus fasciatus

Abstract The adipokinetic hormone (AKH) of the large milkweed bug Oncopeltus fasciatus is isolated from an acidified methanolic extract of 200 corpora cardiaca, purified by single step reversed phase high‐performance liquid chromatography (HPLC) and N‐terminally deblocked using pyroglutamate aminopeptidase. The sequence is identified by Edman degradation and matrix assisted laser desorption/ionization‐time of flight mass spectroscopy as pGlu‐Leu‐Asn‐Phe‐Ser‐Pro‐Asn‐Trp amide. This structure is confirmed by chemical synthesis and coelution of native and synthetic peptide on HPLC. The AKH of O. fasciatus is identical to Tenmo‐HrTH, a member of the adipokinetic/red pigment‐concentrating hormone peptide family that had been isolated earlier from several tenebrionid beetles. Tenmo‐HrTH causes a significant rise in the concentration of haemolymph lipids when injected into adult male and female O. fasciatus, but displays no hyperglycaemic activity. There is no indication of the presence of other AKHs in O. fasciatus. The large milkweed bug represents the first member of the seed bugs (Lygaeidae) for which the endogenous AKH has been identified.     

An energetic analysis of host plant selection by the large milkweed bug,Oncopeltus fasciatus

Summary The large milkweed bug, Oncopeltus fasciatus, is a specialized seed feeder that has been observed completing nymphal development in the field on only a small proportion of its potential host species within the genus Asclepias. In central Missouri only two of the six milkweed species studied, A. syriaca and A. verticillata, commonly supported nymphal O. fasciatus growth in the field. The seed of all six species, however, was equally suitable food for bugs reared in the laboratory. In laboratory preference tests, adult bugs chose to feed on the largest seeds, A. hirtella, but such a preference could not explain the observed field feeding patterns.One explanation to account for the observed host plant selection is based upon an energetic analysis. Only A. syriaca provided enough seed biomass for a clutch of O. fasciatus nymphs to develop on a single plant, and only A. verticillata grew in high enough density that a clutch could find sufficient food within the limited range of nymphal movement. These results illustrate a corollary of the resource concentration hypothesis: within a plant group whose members share similar secondary plant chemistries, the only species that will be viable hosts for a specialized herbivore are those that provide the minimal resource density necessary for the completion of nymphal development.In central Missouri, O. fasciatus has specialized on a critical resource density, not traits of individual Asclepias species. The appearance of host selection within the potential host plant spectrum is the result of a characteristic growth form, seed output, and dispersion pattern for each milkweed species that makes some species much more likely than others to produce sufficient seed resources.     

Ouabain-resistant Na,K-ATPases and cardenolide tolerance in the large milkweed bug,Oncopeltus fasciatus

Oncopeltus fasciatus tolerated 1954× and 7288×, respectively, the LD₅₀ ouabain dose of Schistocerca gregaria and Periplaneta americana when ouabain was injected into the haemocoel of these insects. The maximal ouabain dose that could be injected into O. fasciatus (200 nmol) resulted in no mortality; this dose is higher than the lethal ouabain doses recorded for vertebrates and invertebrates. The ouabain concentration resulting in 50% inhibition (I₅₀) of Na,K-ATPase activity was determined in lyophilates of nervous tissue of O. fasciatus and brain and recta of S. gregaria and were 2.0 × 10⁻⁴, 2.0 × 10⁻⁶ and 1.0 × 10⁻⁶ M, respectively. The I₅₀ value for ouabain inhibition of Na,K-ATPase activity in the nervous tissue of O. fasciatus is higher than the I₅₀ values for nervous tissue in most other insects as well as many other invertebrate and vertebrate tissues. Thus, the presence of ouabain-resistant Na,K-ATPases appears to be a factor in the tolerance and sequestration of plant cardenolides in O. fasciatus.     

Male influence on the duration of reproductive diapause in the large milkweed bug, Oncopeltus fasciatus

ABSTRACT. Differences were found in duration of diapause, as measured by days to first oviposition following adult eclosion, between female Oncopeltus fasciatus (Dallas) mated with male O.sandarachatus (Say) (mean =55 days), and those mated with their brothers (mean =99 days). Under the same conditions (LD 11:13 at 23°C), O.sandarachatus pairs showed no delay in reproduction (mean = 12 days). Male O.sandarachatus exhibit greater sexual activity than male O.fasciatus , and it is postulated that this behaviour may play a significant role in determining the length of diapause in the female.     

Vitellogenesis in the milkweed bug,Oncopeltus fasciatus Dallas (Hemiptera). A light and electron microscopic investigation

Histochemical and electron microscopic methods have revealed that there are four types of cell inclusions in the late vitellogenic oocytes of Oncopeltus. (a) Type 1 is a vacuole which seems to be contributed from the tropharium via the nutritive tubes. It is suggested that this type consists partly at least of nucleolus-like material (ribonucleoprotein) emitted from the nuclei of the Zone III trophocytes. (b) Type 2 is lipid yolk which in early stage oocytes seems to be produced in the “Balbiani body.” In the vitellogenic oocytes these lipid spheres are apparently imported by the oocyte from the haemolymph either through the follicle cells, or through the extracellular space in the follicular epithelium. (c) Type 3 is carbohydrate/protein yolk where at least part of the protein (“vitellogenic protein”) is taken up from the haemolymph, transported through the extracellular space in the follicular epithelium, and deposited into the oocyte by pinocytosis. (d) Glycogen is deposited from the early phases of vitellogenesis. The tropharium may contribute, besides Type 1 vacuoles, ribosomes, mitochondria, stacks of annulated lamellae, and “food vacuoles” to the oocytes. Specialized cells which line the tropharium and send projections toward the trophic core have been called “peripheral trophocytes.” Contrary to the regular trophocytes, they contain glycogen and an abundance of Golgi complexes.     

Effect of captivity on genetic variance for five traits in the large milkweed bug (Oncopeltus fasciatus)

Understanding the changes in genetic variance which may occur as populations move from nature into captivity has been considered important when populations in captivity are used as models of wild ones. However, the inherent significance of these changes has not previously been appreciated in a conservation context: are the methods aimed at founding captive populations with gene diversity representative of natural populations likely also to capture representative quantitative genetic variation? Here, I investigate changes in heritability and a less traditional measure, evolvability, between nature and captivity for the large milkweed bug, Oncopeltus fasciatus, to address this question. Founders were collected from a 100-km transect across the north-eastern US, and five traits (wing colour, pronotum colour, wing length, early fecundity and later fecundity) were recorded for founders and for their offspring during two generations in captivity. Analyses reveal significant heritable variation for some life history and morphological traits in both environments, with comparable absolute levels of evolvability across all traits (0-30%). Randomization tests show that while changes in heritability and total phenotypic variance were highly variable, additive genetic variance and evolvability remained stable across the environmental transition in the three morphological traits (changing 1-2% or less), while they declined significantly in the two life-history traits (5-8%). Although it is unclear whether the declines were due to selection or gene-by-environment interactions (or both), such declines do not appear inevitable: captive populations with small numbers of founders may contain substantial amounts of the evolvability found in nature, at least for some traits.