Olfactory responses to milkweed seed extracts in the milkweed bug

Electrophysiological studies showed that milkweed seed extracts have compounds which are stimulating to the olfactory chemoreceptors of the adult milkweed bug, Oncopeltus fasciatus. Ethanol extracts were the most stimulatory. These compounds may function as feeding attractants or stimulants. Sex, starvation, and mating did not affect the olfactory chemoreceptor responses.     

Geographic variation in the effects of temperature on life-history traits in the large milkweed bug Oncopeltus fasciatus

Summary Complete sets of life-history data (sufficient to construct life-tables and calculate intrinsic rates of increase) were collected at each of three constant temperatures for descendants of two tropical populations of the Large Milkweed Bug, Oncopeltus fasciatus. Although the two populations occur only about 60 km apart, they experience quite different thermal regimes, with little variation in mean monthly temperature at either site. In addition to the pronounced effect of ambient temperature on life-history traits, significant population-by-temperature interactions were observed for six of the eight traits examined. The data and the recent history of the species' distribution are consistent with the hypothesis that natural selection in the cool habitat has favored improved survival and increased reproduction at cool temperatures, with some trade-offs with respect to performance at higher (but ecologically relevant) temperatures.     

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.     

The effect of host plant phenology on reproduction of the milkweed bug,Oncopeltus fasciatus,in tropical Florida

Summary A field study of the relationship between host plant phenology and the reproductive pattern of the large milkweed bug, Oncopeltus fasciatus, was conducted in south Florida. Since O. fasciatus need seeds of either milkweed or Nerium oleander plants to reproduce, reproduction takes place on only those host plants that are producing seed pods.Two of four major host plants, Asclepias incarnata and Sarcostemma clausa fruit seasonally, producing pods in early autumn and early winter, respectively. The third milkweed host, Asclepias curassavica, produces almost no pods midsummer (although it flowers abundantly) and few pods midwinter. Nerium oleander (Apocynaceae) produces some pods all year but is only used by O. fasciatus in the summer when milkweeds are not producing pods. Correspondingly, reproduction of O. fasciatus has been observed year round, but relatively few females reproduce in midwinter, coinciding with decreased pod production and low temperatures. This pattern is consistent with the hypothesis that a photoperiodic cue of short day lengths under conditions of cool temperatures may cause adult females to enter diapause and delay reproduction in the field.A comparison of plant phenologies and rainfall between 1976, a very dry year, and 1978, a year with normal rainfall, showed that extreme dryness disrupted the seasonal fruiting of the milkweeds and consequently the reproduction of O. fasciatus.     

RNA synthesis in the follicular epithelium of the milkweed bug ovary

Sucrose density gradient analysis of the synthesis of ribosomal RNA during follicle cell maturation has revealed two distinct peaks of synthesis. The first of these is the largest and occurs during the transition from the delta to the gamma stages of oöcyte development. It is postulated that this increase in ribosomal synthesis is associated with both yolk uptake and subsequent growth of the follicular epithelium. A second, smaller, increase in the rate of synthesis occurs during the transition from the beta to the alpha₁ condition and this appears to be associated with the synthesis of the chorion by the follicular epithelium.     

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.     

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.     

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.     

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.     

Insecticidal effect of Canavalia ensiformis major urease on nymphs of the milkweed bug Oncopeltus fasciatus and characterization of digestive peptidases

Jackbean (Canavalia ensiformis) ureases are entomotoxic upon the release of internal peptides by insect’s digestive enzymes. Here we studied the digestive peptidases of Oncopeltus fasciatus (milkweed bug) and its susceptibility to jackbean urease (JBU). O. fasciatus nymphs fed urease showed a mortality rate higher than 80% after two weeks. Homogenates of midguts dissected from fourth instars were used to perform proteolytic activity assays. The homogenates hydrolyzed JBU in vitro, yielding a fragment similar in size to known entomotoxic peptides. The major proteolytic activity at pH 4.0 upon protein substrates was blocked by specific inhibitors of aspartic and cysteine peptidases, but not significantly affected by inhibitors of metallopeptidases or serine peptidases. The optimal activity upon N-Cbz-Phe-Arg-MCA was at pH 5.0, with complete blockage by E-64 in all pH tested. Optimal activity upon Abz-AIAFFSRQ-EDDnp (a substrate for aspartic peptidases) was detected at pH 5.0, with partial inhibition by Pepstatin A in the pH range 2-8. Fluorogenic substrates corresponding to the N- and C-terminal regions flanking a known entomotoxic peptide within urease sequence were also tested. While the midgut homogenate did not hydrolyze the N-terminal peptide, it cleaved the C-terminal peptide maximally at pH 4.0-5.0, and this activity was inhibited by E-64 (10 ??M). The midgut homogenate was submitted to ion-exchange chromatography followed by gel filtration. A 22 kDa active fraction was obtained, resolved in SDS-PAGE (12%), the corresponding band was in-gel digested by trypsin, the peptides were analyzed by mass spectrometry, retrieving a cathepsin L protein. The purified cathepsin L was shown to have at least two possible cleavage sites within the urease sequence, and might be able to release a known insecticidal peptide in a single or cascade event. The results suggest that susceptibility of O. fasciatus nymphs to jackbean urease is, like in other insect models, due mostly to limited proteolysis of ingested protein and subsequent release of entomotoxic peptide(s) by cathepsin-like digestive enzymes.     

Early patterning and blastodermal fate map of the head in the milkweed bug Oncopeltus fasciatus

The process of head development in insects utilizes a set of widely conserved genes, but this process and its evolution are not well understood. Recent data from Tribolium castaneum have provided a baseline for an understanding of insect head development. However, work on a wider range of insect species, including members of the hemimetabolous orders, is needed in order to draw general conclusions about the evolution of head differentiation and regionalization. We have cloned and studied the expression and function of a number of candidate genes for head development in the hemipteran Oncopeltus fasciatus. These include orthodenticle, empty spiracles, collier, cap ‘n’ collar, and crocodile. The expression patterns of these genes show a broad conservation relative to Tribolium, as well as differences from Drosophila indicating that Tribolium + Oncopeltus represent a more ancestral pattern. In addition, our data provide a blastodermal fate map for different head regions in later developmental stages and supply us with a “roadmap” for future studies on head development in this species.     

The distribution and function of serotonin in the large milkweed bug,Oncopeltus fasciatus. a comparative study with the blood-feeding bug,Rhodnius prolixus

The blood-feeding hemipteran, Rhodnius prolixus, ingests a large blood meal at the end of each larval stage. To accommodate and process this meal, its cuticle undergoes plasticisation, and its gut and Malpighian tubules respectively absorb and secrete a large volume of water and salts for rapid diuresis. Serotonin has been found to be integral to the feeding process in this animal, along with a diuretic peptide(s). The large milkweed bug, Oncopeltus fasciatus, tends to feed in a more continuous and abstemious manner, and therefore may have different physiological requirements than the blood feeder. Unlike R. prolixus, O. fasciatus is lacking serotonin-like immunoreactive dorsal unpaired median neurons in the mesothoracic ganglionic mass, and lacks serotonin-like immunoreactive neurohaemal areas and processes on the abdominal nerves, integument, salivary glands, and anterior junction of the foregut and crop. The salivary glands and crop do, however, respond to serotonin with increased levels of cAMP, while the integument and Malpighian tubules do not. In addition, O. fasciatus Malpighian tubules respond to both O. fasciatus and R. prolixus partially purified CNS extracts, which are likely to contain any native diuretic peptides. Thus, while serotonin and diuretic peptides may be involved in tubule control in R. prolixus, the latter may be of greater importance in O. fasciatus.     

Composition of scents from the larva of the milkweed bug Oncopeltus fasciatus

The dorsal abdominal scent glands of the larva of Oncopeltus fasciatus may have different, although not necessarily unrelated, functions. It has been found that oct-2-en-1-al is the major component of the scent from the anterior gland, 4-oxo-oct-2-en-1-al the major component of the scent from the posterior gland, and that the larva releases the secretion from the posterior gland more readily than it does from the anterior gland. Minor components of the scents include hex-2-en-1-al, 4-oxohex-2-en-1-al, and possibly hept-2-en-1-al. The secretions, after release onto the dorsal surface of the abdomen, are subsequently brushed off with the hind tarsi onto the surface on which the larva is standing. This behaviour can be elicited by stimulating the dorsal abdominal surface of the larva with the vapour of octenal and similar aldehydes.