Changes associated with laboratory rearing in antennal sensilla patterns of Triatoma infestans, Rhodnius prolixus, and Rhodnius pallescens (Hemiptera, Reduviidae, Triatominae)

We examined changes in the array of antennal sensilla of three species of Triatominae (Triatoma infestans, Rhodnius prolixus, and R. pallescens) following their establishment for different periods in laboratory culture. In each case, the laboratory colonies were compared with conspecific samples taken directly from the field, by quantitative analysis of the sensilla arrays on the three distal segments of the antenna in terms of the densities of three types of chemoreceptors (basiconics and thick and thin walled trichoids) and one type of mechanoreceptor (bristles). Sensilla densities were compared by ANOVA or non-parametric tests, and by multivariate discriminant analysis. Strains of the same species reared in different laboratories showed significant differences in their sensilla arrays, especially when compared to field-collected material from the same geographic origin. A Bolivian strain of T. infestans reared in the laboratory for 15 years and fed at monthly intervals, showed greatest differences from its conspecific wild forms, especially in terms of reductions in the number of chemoreceptors. By contrast, an Argentine strain of T. infestans reared for 25 years in the laboratory and fed weekly, showed a relative increase in the density of mechanoreceptors. A Colombian strain of R. prolixus reared for 20 years and fed weekly or fortnightly, showed only modest differences in the sensilla array when compared to its wild populations from the same area. However, a Colombian strain of R. pallescens reared for 12 years and fed fortnightly, did show highly significant reductions in one form of chemoreceptor compared to its conspecific wild populations. For all populations, multivariate analysis clearly discriminated between laboratory and field collected specimens, suggesting that artificial rearing can lead to modifications in the sensory array. This not only supports the idea of morphological plasticity in these species, but also suggests caution in the use of long-established laboratory material for experimental studies designed to extrapolate the natural behaviour and physiology of these species.     

Antennal sensilla of Rhodnius

By scanning electron microscopy, sensilla type and distribution were studied on the antennae of ten species of Rhodnius. No sexual dimorphism was apparent. Intraspecific differences in sensillar pattern were shown to be potentially useful in species determination and to agree with results from biochemical studies and previous morphometric studies in terms of species affinities. © 1994 Wiley-Liss, Inc.     

Differentiation and genetic analysis of Rhodnius prolixus and Rhodnius colombiensis by rDNA and RAPD amplification.

Domiciliated Rhodnius prolixus and sylvatic R. colombiensis were analyzed in order to confirm their genetic divergence and verify the risk that the latter represents in the domiciliation process, and to provide tools for identifying the sources of possible reinfestation by triatomines in human dwellings allowing control programs to be undertaken. Comparison of random amplified polymorphic DNA amplification patterns and cluster analysis suggests reproductive discontinuity between the two species. The calculated statistical F value of 0.24 and effective migration rate of 0.6 individuals per generation are insufficient to maintain genetic homogeneity between them and confirm the absence of present genetic flow. R. colombiensis presents higher intrapopulation variability. Polymerase chain reaction of ribosomal DNA supports these findings. The low genetic flow between the two species implies that R. colombiensis do not represent an epidemiological risk for the domiciliary transmission of Trypanosoma cruzi in the Tolima Department. The lower variability of the domiciliated R. prolixus could result in greater susceptibility to the use of pesticides in control programs.     

Heme biosynthesis and oogenesis in the blood-sucking bug, Rhodnius prolixus

We have previously shown that the pathway of porphyrin synthesis operates in the blood feeding triatomine bug Rhodnius prolixus but not in the cattle tick Boophilus microplus. In the present paper we studied the correlation between heme synthesis and egg development in Rhodnius. There is a sharp increase heme biosynthetic capability in the fat body (160%) and in the ovaries (360%) in response to a blood meal, as evaluated from the activity of the enzyme delta-aminolevulinate dehydratase (EC 4.2.1.24). The in vivo inhibition of ALA-D by succinyl acetone results in a dose dependent decrease of oviposition. Oviposition is recovered when porphobilinogen, the product of the impaired reaction, is added to the succinyl acetone enriched blood. Taken together, these results show that heme biosynthesis is a fundamental event to vitellogenic females. The demand for heme in this metabolic juncture cannot be supplied by the heme eventually absorbed during blood digestion and associated with Rhodnius heme binding protein (RHBP), which is then incorporated into growing oocytes. Inhibition of heme biosynthesis results in lower levels of RHBP in the hemolymph, suggesting that the synthesis of this protein is controlled by heme availability.     

Immune depression in Rhodnius prolixus by seco-steroids, physalins

A comparative study of the effects of physalins, seco-steroidal substances of Physalis angulata (Solanaceae), on the immune reactions of R. prolixus was carried out. Ecdysis and mortality were not affected by treatment with physalins B, D, F or G (1-10 microg/ml of blood meal). R. prolixus larvae fed with blood containing physalins and inoculated with 1 microl of Enterobacter cloacae beta12 (5 x 10(3)/insect) exhibited mortality rates three times higher than controls. The insects treated with physalin B, and F (1 microg/ml) and inoculated with E. cloacae beta12 showed significant differences on lysozyme activity in the hemolymph compared to untreated insects. Furthermore, physalin D (1 microg/ml) significantly reduced the antibacterial activity. Concerning cellular immune reactions, all insects treated with physalins (1 microg/ml), exhibited drastic reductions in the quantity of yeast cell-hemocyte binding and subsequent internalization. Insects inoculated with bacteria and treated with physalins B, F and G showed reductions of microaggregate formation but physalin D did not. Physalins B and F also reduced total hemocyte count in the hemolymph. These results suggest that, in different ways, probably due to their different chemical structures, physalin B, D, F and G are immunomodulatory substances for the bloodsucking insect, R. prolixus.     

Uptake of Rhodnius heme-binding protein (RHBP) by the ovary of Rhodnius prolixus

The uptake of RHBP (Rhodnius heme-binding protein) by the ovaries of Rhodnius prolixus was characterized. RHBP purified from oocyte was labeled with ¹²⁵I and used to study the process of uptake by the ovary in vivo and in vitro. After injection, the [¹²⁵I]RHBP was readily removed from the hemolymph and accumulated especially in the ovary. The capacity of the ovary to take up [¹²⁵I]RHBP from the hemolymph varied during the days following blood meal. It increased up to day 2, remained stable until day 5, and then decreased up to the end of oogenesis. In vitro, the uptake of [¹²⁵I]RHBP was linear at least up to 60 min. The uptake was dependent on [¹²⁵I]RHBP concentration and showed to be a saturable process. The addition of a molar excess of non-related proteins such as Vitellin (Vt), Lipophorin (Lp), and Bovine Serum Albumin (BSA) did not reduce [¹²⁵I]RHBP uptake. Using immunogold technique the RHBP was localized at the microvilli, coated pits, and yolk granules. The main yolk protein, Vt, did not compete with RHBP for the uptake. Thus, it is discussed here that they bind to independent binding sites of the oocytes, and are directed later on to the same compartment. The need of both proteins for the completion of mature oocyte was verified in vivo. The reduction of heme-RHBP in the hemolymph, by changing the diet, decreased the number of eggs laid. Increasing the concentration of heme-RHBP in the hemolymph, the number of eggs produced increased in a dose dependent manner. In vitro, both apo-RHBP and heme-RHBP can be taken up by the oocyte. Since the mature oocyte contains only heme-saturated RHBP, the possible fate of apo-RHBP is also discussed. Arch. Insect Biochem. Physiol. 39:133–143, 1998. © 1998 Wiley-Liss, Inc.     

Comparative dissection of the peripheral olfactory system of the Chagas disease vectors Rhodnius prolixus and Rhodnius brethesi

American trypanosomiasis, or Chagas disease, is transmitted by both domestic and sylvatic species of Triatominae which use sensory cues to locate their vertebrate hosts. Among them, odorants have been shown to play a key role. Previous work revealed morphological differences in the sensory apparatus of different species of Triatomines, but to date a comparative functional study of the olfactory system is lacking. After examining the antennal sensilla with scanning electronic microscopy (SEM), we compared olfactory responses of Rhodnius prolixus and the sylvatic Rhodnius brethesi using an electrophysiological approach. In electroantennogram (EAG) recordings, we first showed that the antenna of R. prolixus is highly responsive to carboxylic acids, compounds found in their habitat and the headspace of their vertebrate hosts. We then compared responses from olfactory sensory neurons (OSNs) housed in the grooved peg sensilla of both species, as these are tuned to these compounds using single-sensillum recordings (SSRs). In R. prolixus, the SSR responses revealed a narrower tuning breath than its sylvatic sibling, with the latter showing responses to a broader range of chemical classes. Additionally, we observed significant differences between these two species in their response to particular volatiles, such as amyl acetate and butyryl chloride. In summary, the closely related, but ecologically differentiated R. prolixus and R. brethesi display distinct differences in their olfactory functions. Considering the ongoing rapid destruction of the natural habitat of sylvatic species and the likely shift towards environments shaped by humans, we expect that our results will contribute to the design of efficient vector control strategies in the future.     

Spatial complexity and the fitness of the kissing bug, Rhodnius prolixus

Abstract:  Rhodnius prolixus Stål (Reduviidae: Rhodninii) is one of the most important vectors of Chagas disease. As a result of its medical importance, several life history studies have been carried out, but in general with a restricted demographical scope, without assessing the potential tradeoffs in the life history of this insect. In this study, individuals of R. prolixus were kept in two spatially different habitats and several fitness components were measured. The results show that life expectancy in adults is negatively correlated with gross fecundity, indicating a cost of reproduction. Life expectancy is shorter for males and longer for individuals of the same sex in the more complex habitat, where the fitness is lower compared with that of the simpler habitat.     

Identification of kinin-related peptides in the disease vector, Rhodnius prolixus

We have used an in silico approach to identify a gene from the blood-gorging vector, Rhodnius prolixus, that is predicted to produce an insect kinin prepropeptide. The prepropeptide is 398 amino acids in length and can potentially produce a large number of kinin-related peptides following post-translational processing. A comparison with other insect kinin precursor sequences demonstrates greatest conservation at the C-terminal region of the kinin peptides. Multiple peptides predicted from the kinin gene are phenotypically expressed in R. prolixus, as revealed by MALDI-TOF MS MS, including 12 kinins and one kinin precursor peptide (KPP). Six of these peptides are characterized by the typical insect kinin C-terminal motif FX₁X₂WGamide and five of these are also found as truncated forms. Five peptides were identified with an atypical, though similar, FX₁X₂WAamide C-terminus. There is also peptide with a C-terminal DDNGamide motif and a number of non-amidated peptides.     

Circadian orchestration of developmental hormones in the insect, Rhodnius prolixus

This review presents a new perspective on the circadian regulation and functions of insect developmental hormones. In Rhodnius prolixus (Hemiptera), the brain neuropeptide prothoracicotropic hormone (PTTH) is released with a circadian rhythm that is controlled by paired photosensitive clocks in the brain. These clocks comprise the dorsal and lateral PER/TIM clock neurons known to regulate behavioral rhythms in Drosophila. Axons of PTTH and clock cells make close contact. Photosensitive PER/TIM clocks also reside in the paired prothoracic glands (PGs), which generate rhythmic synthesis and release of the ecdysteroid molting hormones. The PG clocks are entrained by both light and PTTH. These four clocks are coupled together by both nerves and hormones into a timing system whose primary regulated output is the circadian rhythm of ecdysteroids in the hemolymph. This complex timing system appears necessary to ensure circadian organization of the gene expression that is induced in target cells by ecdysteroids via circadian cycling of the nuclear ecdysteroid receptor (EcR). This multioscillator system serves to transduce 'the day outside' into endocrine rhythms that orchestrate 'the day inside'. It has many functional similarities with vertebrate circadian systems.     

The neuropeptidome of Rhodnius prolixus brain

We show a sensitive and straightforward off‐line nano‐LC‐MALDI‐MS/MS workflow that allowed the first comprehensive neuropeptidomic analysis of an insect disease vector. This approach was applied to identify neuropeptides in the brain of Rhodnius prolixus, a vector of Chagas disease. This work will contribute to the annotation of genes in the ongoing R. prolixus genome sequence project. Peptides were identified by de novo sequencing and comparisons to known neuropeptides from different organisms by database search. By these means, we were able to identify 42 novel neuropeptides from R. prolixus. The peptides were classified as extended FMRF‐amide‐related peptides, sulfakinins, myosuppressins, short neuropeptide F, long neuropeptide F, SIF‐amide‐related peptides, tachykinins, orcokinins, allatostatins, allatotropins, calcitonin‐like diuretic hormones, corazonin, and pyrokinin. Some of them were detected in multiple isoforms and/or truncated fragments. Interestingly, some of the R. prolixus peptides, as myosuppressin and sulfakinins, are unique in their characteristic C‐terminal domain among insect neuropeptides identified so far.     

The role of eicosanoids on Rhodnius heme-binding protein (RHBP) endocytosis by Rhodnius prolixus ovaries

The participation of eicosanoids and second messengers on the regulation of RHBP endocytosis by the ovaries was investigated, using [(125)I]RHBP in experiments in vivo and in vitro. Addition of PGE(2) (one of the products of the cyclooxygenase pathway) decreased in vitro the uptake of RHBP by 35%. The rate of RHBP endocytosis increased in the presence of indomethacin, a potent cyclooxigenase inhibitor, up to 50% in vitro and up to 55% in vivo, thus giving support to the role of cyclooxygenase derivatives on endocytosis regulation. The amount of PGE(2) secreted to the culture medium by the cells of Rhodnius prolixus ovaries was 1.1 ng/ovary following RHBP uptake assay. The amount of PGE(2) decreases approximately 25% in the presence of 5 microM indomethacin. Using a scanning electron microscope we have observed that neither the surface area nor the patencies of follicle cells were affected by treatment with indomethacin, thus suggesting that, its effect is elicited in the oocyte. Finally, we have identified two ovarian peptides that were dephosphorylated after the indomethacin treatment (18 and 25 kDa). Taken together these data show that local mediators such as eicosanoids act upon the oocytes controlling RHBP endocytosis, perhaps using the protein phosphorylation signal transduction pathway.     

Effects of lignoids on a hematophagous bug, Rhodnius prolixus: feeding, ecdysis and diuresis

The effects of lignoids on feeding, ecdysis and diuresis in fourth-instar larvae of Rhodnius prolixus (Hemiptera) were investigated. Up to 100 microg/ml burchellin, podophyllotoxin, pinoresinol, sesamin, licarin A, or nordihydroguaiaretic acid (NDGA) in the diet did not induce antifeedant effects. Pinoresinol and NDGA significantly inhibited ecdysis. In experiments in vivo, burchellin and podophyllotoxin reduced the production of urine after feeding. 5-Hydroxytryptamine (5-HT), a diuretic hormone, partially counteracted this effect of burchellin. In experiments in vitro, using isolated Malpighian tubules, (i) burchellin reduced diuretic hormone levels in the hemolymph but not the amount of diuretic hormone stored in the thoracic ganglionic masses (including axons), (ii) burchellin decreased the volume of urine secreted by isolated Malpighian tubules, and (iii) 5-HT could not overcome the effect of burchellin upon the Malpighian tubules. We conclude that burchellin interfered with the release, but not with the production of diuretic hormone by the thoracic ganglionic mass or induced an antidiuretic hormone and directly affected the Malpighian tubules.