Indicators of infestation, colonization and infection of Triatoma dimidiata (Latreille) (Hemiptera: Reduviidae) in Campeche, México

Triatoma dimidiata (Latreille) is considered to be one of the primary vectors of Chagas disease in Southern Mexico and Central America. The objective of the present study was to obtain ecological information on T. dimidiata in two rural communities of Campeche, Mexico, where the vector is poorly studied. Our work consisted of monthly samplings carried out during one-year time at three levels: sylvatic, peridomestic and intradomestic, in order to estimate the population abundance of this species and its rate of infection with Trypanosoma cruzi. Triatoma dimidiata was the unique vector of this disease collected in San Juan Bautista Sakcabchen (SJBS) and Crucero San Luis (CSL). The total of 145 individuals were captured in SJBS; from these, 26.9%, 20% and 53.1% were collected in the sylvatic, peridomestic and intradomestic area, respectively. In CSL captures yielded 108 individuals: 40.7% in the sylvatic area, 20.4% peridomestic and 38.9% intradomestic. We found no correlation between climatic variables and population abundance of T. dimidiata. Dataset obtained suggests that individuals from the sylvatic area exhibit a high rate of natural infection by T. cruzi, with monthly percentages up to 61.5% for SJBS and 50% for CSL. At the peri and intradomestic level, the reservoirs apparently play an important role in the transmission, as the seroprevalence in dogs was 61.5% y 65.4%, for SJBS y CSL, respectively. Based on these findings, it was concluded that inhabitants of both communities are at a high risk of Chagas disease infection.     

Peridomiciliary colonies of Triatoma vitticeps (Stal, 1859) (Hemiptera, Reduviidae, Triatominae) infected with Trypanosoma cruzi in rural areas of the state of Espírito Santo, Brazil

In Brazil, the colonization of human dwellings by triatomines occurs in areas with native vegetation of the caatinga or cerrado types. In areas of Atlantic forest such as in the Brazilian state of Espírito Santo, there are no species adapted to live in human habitations. The few autochthonous cases of Chagas disease encountered in Espírito Santo have been attributed to adult specimens of Triatoma vitticeps that invade houses from forest remnants. In recent years, the entomology unit of the Espírito Santo State Health Secretariat has recorded nymphs infected with flagellates similar to Trypanosoma cruzi in rural localities. Entomological surveys were carried out in the residences and outbuildings in which the insects were found, and serological examinations for Chagas disease performed on the inhabitants. Four colonies were found, all associated with nests of opossums (Didelphis aurita), 111 specimens of T. vitticeps, and 159 eggs being collected. All the triatomines presented flagellates in their frass. Mice inoculated with the faeces presented trypomastigotes in the circulating blood and groups of amastigotes in the cardiac muscle fibres. Serological tests performed on the inhabitants were negative for T. cruzi. Even with the intense devastation of the forest in Espírito Santo, there are no indications of change in the sylvatic habits of T. vitticeps. Colonies of this insect associated with opossum nests would indicate an expansion of the sylvatic environment into the peridomicile.     

Molecular Population Genetics and Evolution of the Chagas’ Disease Vector Triatoma infestans (Hemiptera: Reduviidae)

Triatoma infestans (Klug) is the main vector of Chagas’ disease in the Southern Cone of Latin America between the latitudes 10° S and 46° S. The long-term effectiveness of the control campaigns is greatly dependent upon the vector population structure. Mitochondrial DNA (mtDNA) genes have been used in a number of T. infestans population genetic analyses. However, the maternally inherited markers as well as nuclear ribosomal DNA analyzed until the present exhibited low or limited levels of variation. Analyses based on microsatellite markers strongly supported the existence of some type of stratification in T. infestans populations and supported the hypothesis of vector population recovery from survivors of the insecticide-treated areas, highlighting the value of population genetic analyses in assessing the effectiveness of Chagas’ disease vector control programmes. Although phylogeographic studies have generally suggested a Bolivian Andean origin of T. infestans, they recovered two reciprocal monophyletic groups of T. infestans and Bolivian populations who were not basal as expected for an ancestral group. In addition, a non-Andean origin could not be excluded by mtDNA genealogies that included sylvatic bugs from Gran Chaco. On the other side, mitochondrial and microsatellite markers supported the hypothesis of two independent migration events of colonization and secondary contacts in southern South America. Since the phylogenetic analyses remain inconclusive, more sequences, not only from mitochondrial genes but also from nuclear genes, need to be examined.     

Comparative study of the stridulatory sulcus,buccula and rostrum of the nymphs of Triatoma guazu Lent & Wygodzinsky, 1979 and Triatoma jurbergi Carcavallo,Galvão & Lent, 1998 by scanning electron microscopy (Hemiptera,Reduviidae)

The ultrastructural morphology of the ventral region of the head (rostrum and buccula) and proesternum (stridulatory sulcus) of nymphs from the 1st to 5th instars of Triatoma guazu Lent & Wygodzinsky, 1979 and Triatoma jurbergi Carcavallo, Galv?o & Lent, 1998 was described. Morphological differences between the two species and of the five nymphal stages development of each species were observed. These structures showed systematic differential characteristics of the studied species and may be used to increase their taxonomic range.     

First report of Triatoma nigromaculata (Stål, 1859) (Hemiptera, Reduviidae, Triatominae) for Colombia

The presence of Triatoma nigromaculata was recorded for the first time in Colombia in the rural village La Playa in the province of Cauca. A single female was captured from an outdoor area near a household. The presence of Trypanosoma parasites in the specimen was not established due to the poor condition of the specimen. The epidemiological importance of this finding is discussed with respect to the potential for transmission of Chagas disease in the province of Cauca and, more broadly, in Colombia.     

Development of genital plates in nymphs of Triatoma pallidipennis, Stål 1872, (Hemiptera: Reduviidae) and its application as sexing method

Searching for morphometric differences between sexes in immature forms, the development of genital plates in the exuviae of Triatoma pallidipennis St?l 1872 nymphs was studied. Differences were found in the form and size of the 9th genital urosternite, it is larger and wider in males as compared to females. This difference is reported in several South American Triatoma species. From our results it is possible to sex early stages from microscopic observation of genital plates in whole insects.     

Evaluation of RbCl and CrCl₃ as markers of Triatoma brasiliensis (Hemiptera: Reduviidae) nymphs: persistence and influence of Rb and Cr on triatomine biology

In order to mark Triatoma brasiliensis, the vector of Chagas disease in Brazil, two chemical compounds, rubidium chloride (RbCl) and chromium chloride (CrCl?), were tested. First, 199 N2-N5 nymphs were fed on blood with 0.025M RbCl. Rb marker positivity ranged from 2.5% (N3)-70% (N2), with a maximum persistence of 98 days. Second, 265 N2-N5 nymphs were fed on blood containing 0.0015M CrCl?. Cr marker positivity ranged up to 93% (N5), with a maximum persistence of 119 days. Finally, we blood fed 213 T. brasiliensis to investigate whether CrCl? altered the biology of this insect. The developmental time of T. brasiliensis was unaltered, but the survival of the Cr-marked group was lower than that of the control group. Differences in the mean fecundity of the control (mean of 156.1) and experimental (mean of 135.6) groups were not statistically significant and 100% of the egg batches of females Cr-marked as nymphs were positive. In conclusion, CrCl? is a useful tool for marking T. brasiliensis nymphs due to its high positivity and persistence.     

New distribution and host records of chalcidoid parasitoids (Hymenoptera: Chalcidoidea) of scale insects (Hemiptera: Coccoidea) in Espírito Santo,Brazil

Three species of chalcidoid parasitoids of scale insects are recorded for the first time in Brazil: Adelencyrtus moderatus, Homalopoda sp., and Diglyphomorpha sp.; and new parasitoid–host associations are recorded between the chalcidoids Encarsia lounsburyi with Hemiberlesia palmae, Encarsia lounsburyi with Melanaspis smilacis, and Diglyphomorpha sp. with Dysmicoccus brevipes.     

Presence of triatominae (Hemiptera, Reduviidae) and risk of transmission of Chagas disease in Colima, México

With the purpose of evaluating the risk of transmission of the Chagas disease in the State of Colima, México, an entomological survey was performed to obtain triatominae and the rate of infection by Trypanosoma cruzi determined by examination of its dejections. Two hundred eighteen houses located in 16 villages were sampled. In each house the intradomestic and peridomestic habitats were examined by the man-hour-house method, sensor boxes and mouse-baited traps. Also, 12 silvatic places were explored around the same areas using the same techniques as the ones sampled. In total, 456 specimens were captured, of which 139 correspond to Triatoma phyllosoma pallidipennis; 80 to T.p. longipennis; one specimen of T. dimidiata and 236 nymphs of Triatoma sp. Two hundred ninety seven insects were captured in the intradomestic habitat, 132 in the peridomestic and 26 in the silvatic. The index of positive houses was 27%, located in the central area of the state. The rate of natural infection with T. cruzi showed 25.6%. This results confirmed the presence of two important vectors of the Chagas disease in Colima. Its preference for the domestic habitat and its high levels of natural infection with T. cruzi suggested the existence of a significant risk for its transmission in this area of the country.     

Distribution and infection of triatomines (Hemiptera: Reduviidae) by Trypanosoma cruzi in the state of Michoacán, Mexico

An entomological study of triatomine species was carried out to assess their prevalence in 10 localities of the state of Michoacán, Mexico. Entomological indices were calculated to estimate the risk for vector-borne transmission of Trypanosoma cruzi to the human population in this area. Four triatomine species (Triatoma barberi, Triatoma dimidiata, Meccus pallidipennis and Meccus longipennis) were collected from the study area. This is the first report of M. longipennis and T. dimidiata in Michoacán. M. pallidipennis was significantly (p < 0.05) more abundant than any of the other species collected in the study area. Infection indices were greater than 50% for each of the four collected triatomine species. Significantly more triatomines were collected from intradomiciliary areas than from peridomiciliary or sylvatic areas. Infestation, crowding and density indices were low, whereas colonisation indices were high in five localities. The current vectorial conditions in the study area require continuous entomological and serological surveillance to diminish the risk of T. cruzi transmission to human populations.     

The food requirements of Phonoctonus nigrofasciatus St?l. (Hemiptera, Reduviidae)

The food requirements of Phonoctonus nigrofassiatus Stål. when fed on nymphs of Dysdercus were investigated. Whithin an instar the conversion ratio varies with the weight of food consumed. Thus, for the first instar nymph the conversion ratio wsa 62.6% when food was limited and 44.3% when food was plentiful. It is suggested that the relationship between conversion ratio and weight food consumed may follow an S-shaped curve. The earlier instars appear to be more efficient than the later ones. This is not merely a further reflection of differing food consumption. The Predatory Value is a variable index which must be used with care when comparing different instars. It is thought that 20–22 fifth instar Dysdercus are necessary to provide the food required for the development of a Phonoctonus from first instar to adult.

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Zusammenfassung Die Nahrungsbedürfnisse von Phonoctonus nigrofasciatus Stål. bei Fütterung mit Dysdercus-Larven wurden untersucht. Innerhalb eines Stadiums variiert die Umsatzrate mit dem Gewicht der aufgenommenen Nahrung. So betrug die Ausnutzungsrate 62.6%, wenn die Nahrungsmenge begrenzt war, und 44.3%, wenn reichlich Futter geboten wurde. Es wird vermutet, daß die Beziehung zwischen Umsatzverhältnis und Gewicht der Nahrung einer S-förmigen Kurve folgt. Die frühen Stadien scheinen wirkungsvoller als die späteren zu sein. Das ist nicht nur eine Folge des unterschiedlichen. Nahrungsverbrauchs. Der Prädator-Wert (Wert als Räuber) ist ein verinderlicher Index, der mit Vorsicht angewendet werden muß, wenn verschiedene Entwicklungsstadien verglichen werden. Es wird angenommen, daß 20 bis 22 fünfte Larvenstadien von Dysdercus erforderlich sind, um den Nahrungsbedarf für die Entwicklung eines Phonoctonus vom ersten Larvenstadium bis zur Imago zu decken.

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This work was carried out in the Department of Zoology and Applied Entomology at the Field Station of Imperial College, Sunninghill, Ascot, Berkshire.     

Biological aspects of Autoplusia egena (Guenée) (Lepidoptera: Noctuidae, Plusiinae)

Autoplusia egena (Guenée) is a moth distributed throughout the Western hemisphere. The larvae have already been found feeding on several different plant families, including important crops such soybeans and beans. To contribute to the knowledge of its biology in laboratory conditions, and considering the duration and the morphometry of each development stage, a laboratorial rearing was accomplished at 25 +/- 1 degrees C, 70 +/- 10% RH and 14h photophase. The larvae were fed with black bean leaves and the adults were fed with a honey solution at 10%. The results, expressed by the mean (+/- SE), for the periods of each stage were: egg 3.0 +/- 0.00 d; larva 15.7 +/- 1.25 d; pre-pupa 1.9 +/- 0.05 d; pupa 8.8 +/- 0.09 d and adult: longevity 12.1 +/- 0.95 d, pre-oviposition 5.4 +/- 0.50 d, oviposition 6.3 +/- 1.10 d and post-oviposition 1.4 +/- 0.87 d. The larvae went through five instars, for which the mean width of the cephalic capsules were 0.302 +/- 0.001 mm; 0.500 +/- 0.003 mm; 0.854 +/- 0.008 mm; 1.424 +/- 0.011 mm and 2.744 +/- 0.053 mm. The average length, width, and weight of the pupae were 16.965 +/- 0.003 mm, 4.674 +/- 0.040 mm and 0.217 +/- 0.003 g, respectively.     

Biology of Triatoma klugi Carcavallo,Jurberg, Lent & Galvão 2001 (Heteroptera: Reduviidae) under laboratory conditions: effects of distinct blood sources and susceptibility to Trypanosoma cruzi and Trypanosoma rangeli

The life cycle of Triatoma klugi Carcavallo, Jurberg, Lent & Galv?o 2001 was compared under laboratory conditions using two groups of the F1 generation obtained from field-collected bugs. Among the 100 nymphs weekly fed on mice (Group A) or chicken (Group B), 77% of Group A and 67% of Group B reached the adult stage, and the mean time from the first nymphal stage to adult was 190.08 +/- 28.31 days and 221.23 +/- 40.50, respectively. The average span in days for each stage per group and the number of blood meals required for each stage were also evaluated. The overall mortality rate was 23% and 33% for Groups A and B, respectively. The mean number of eggs laid per month in a three-month period was of 56.20, 51.70 and 73.20 for Group A, and 64.50, 53.50 and 38.71 for Group B. Despite the blood source, comparative analysis revealed no statistically significant differences in the life cycle of T. klugi under laboratory conditions. Infection rates over 60% were observed for both Trypanosoma cruzi strains tested. Even revealing high infection rates of the hemolymph by T. rangeli strains, T. klugi revealed no salivary gland infections and was not able to transmit the parasite.     

Revalidation and redescription of Triatoma brasiliensis macromelasoma Galv?o, 1956 and an identification key for the Triatoma brasiliensis complex (Hemiptera: Reduviidae: Triatominae)

Triatoma brasiliensis macromelasoma is revalidated based on the results of previous multidisciplinary studies on the Triatoma brasiliensis complex, consisting of crossing experiments and morphological, biological, ecological and molecular analyses. These taxonomic tools showed the closest relationship between T. b. macromelasoma and Triatoma brasiliensis brasiliensis. T. b. macromelasoma is redescribed based on specimens collected in the type locality and specimens from a F1 colony. The complex now comprises T. b. brasiliensis, T. b. macromelasoma, Triatoma melanica, Triatoma juazeirensis and Triatoma sherlocki. An identification key for all members of the complex is presented. This detailed comparative study of the morphological features of T. b. macromelasoma and the remaining members of the complex corroborates results from multidisciplinary analyses, suggesting that the subspecific status is applicable. This subspecies can be distinguished by the following combination of features: a pronotum with 1+1 narrow brownish-yellow stripes on the submedian carinae, not attaining its apex, hemelytra with membrane cells darkened on the central portion and legs with an incomplete brownish-yellow ring on the apical half of the femora. Because the T. brasiliensis complex is of distinct epidemiological importance throughout its geographic distribution, a precise identification of its five members is important for monitoring and controlling actions against Chagas disease transmission.     

Biochemical and cellular characterization of lipophorin–midgut interaction in the hematophagous Panstrongylus megistus (Hemiptera: Reduviidae)

In order to better understand the metabolism of dietary lipids in hematophagous insects, we have performed a biochemical and cellular characterization of lipophorin (Lp)–midgut interaction in Panstrongylus megistus, a vector of Chagas' disease. The study was accomplished by solid-phase binding assays or with iodinated Lp (¹²⁵I-Lp), using midgut membranes from fifth instar nymphs after ecdysis and after insects received a blood meal. Results obtained from both physiological conditions indicated that Lp interacted specifically with the midgut, implying the participation of receptors. Binding capacity of lipophorin to membranes was dependent on the amount of membranes added in the system, reaching saturation at 0.1 μg/ml. However, membranes obtained after a blood meal exhibited higher binding activity. Saturation kinetics results using ¹²⁵I-Lp suggested a single binding site with high affinity for Lp in the midgut membranes (K_d = 5.1 ± 3.6 × 10^?8 M). The unrelated lipoprotein, human LDL, did not compete with Lp for its binding site in the midgut. The binding was dependent on pH and the treatment of membranes with trypsin or heat causes a significant inhibition of the binding. Midgut–Lp interaction was affected by changes in ionic strength and by suramin, but showed no requirement of calcium. Ligand blotting assays revealed two membrane proteins that specifically bound Lp (61 and 45 kDa). At cellular level, Lp binding sites were located mainly at the basal plasma membrane of isolated enterocytes. Labeled Lp with fluorescent probes directed to its proteins or its phospholipids fraction co-localized mainly at the basement membrane of the midgut. In addition, no intracellular Lp was observed at any condition. The lack of an endocytic pathway for Lp in the midgut of P. megistus is analyzed in the context of insect physiology.     

Two new species of Campomanesia (Myrtaceae) from Espírito Santo and Bahia, Brazil

Campomanesia macrobracteolata andC. anemonea, apparently closely related species from Espírito Santo and Bahia, Brazil, are described as new and are illustrated. Comparisons are made with two other similar species.     

Macrogeographic and microgeographic genetic structure of the Chagas’ disease vector <Emphasis Type="Italic">Triatoma infestans</Emphasis> (Hemiptera: Reduviidae) from Catamarca,Argentina

The genetic structure in populations of the Chagas' disease vector Triatoma infestans from six localities belonging to areas under the same insecticide treatment conditions of Catamarca province (Argentina) was examined at macrogeographical and microgeographical scales. A total of 238 insects were typed for 10 polymorphic microsatellite loci. The average observed and expected heterozygosities ranged from 0.319 to 0.549 and from 0.389 to 0.689, respectively. The present results confirm that populations of T. infestans are highly structured. Spatial genetic structure was detectable at macrogeographical and microgeographical levels. Comparisons of the levels of genetic variability between two temporal samples were carried out to assess the impact of the insecticide treatment. The genetic diversity of the population was not significantly affected after insecticide use since different genetic parameters (allele number, observed and expected heterozygosities) remained stable. However, loss of low frequency alleles and not previously found alleles were detected. The effective population size (N(e)) estimated was substantially lower in the second temporal sample than in the first; nevertheless, it is possible that the size of the remnant population after insecticide treatment was still large enough to retain the genetic diversity. Very few individuals did not belong to the local T. infestans populations as determined by assignment analyses, suggesting a low level of immigration in the population. The results of the assignment and first-generation migrant tests suggest male-biased dispersal at microgeographical level.     

Characterisation of a cytoplasmic male-sterile hybrid line between Lycopersicon peruvianum Mill. ×Lycopersicon pennellii Corr. and its crosses with cultivated tomato

 The cytoplasmic male-sterile (CMS) line CMS-pennellii (BC₁₀P₂ L. peruvianum×L. pennellii) and its complex hybrids with L. esculentum were studied. The established sterility was classified as the sporogenous type. As a result of the interaction of the genome of L. pennellii and the cytoplasm of L. peruvianum clear changes were established in the profiles of malic enzyme and esterase. Restriction fragment length polymorphism (RFLP) was detected between the mitochondrial (mt) genomes of CMS-pennellii and the cytoplasm donor, L. peruvianum, for two mtDNA probes: atpA and nad3. The established differences in the isozyme pattern and mt genomes are considered as useful markers to distinguish fertile and sterile plants. A breakthrough in the unilateral incompatibility of CMS-pennellii and the incorporation of the genome of L. esculentum on a CMS background is reported. The analysis of the complex hybrids assumes the interaction of two dominant genes – a maintainer gene from L. pennellii and a restorer gene from cultivated tomato. The hybrids produced with L. esculentum provide the basis for the development of a CMS system in cultivated tomato. Received: 25 May 1998 / Accepted: 26 August 1998