Influence of the blood meal source on the biology of Meccus picturatus Usinger 1939 (Hemiptera: Reduviidae: Triatominae) under laboratory conditions

Aspects related to hatching, time-lapse between presenting the blood meal and beginning of feeding, feeding time, postfeed defecation delay,life time, mortality and fecundity for each stage of Meccus picturatus, life-cycle were evaluated and compared in two cohorts of M. picturatus fed on hens or rabbits. The hatching rate observed for each of the two studied groups of eggs was 78.1% (n = 2298) on the group fed on hens and 82.1% (n = 2704) on that fed on rabbits, and the average time of hatching was 20 days. Mean time-lapse for beginning feeding was under 3 min in nymphal stages and postfeed defecation delay was under 10 min in all stages, in both cohorts. Mean feeding time was significantly (P < 0.05) shorter in triatomines fed on hens than on rabbits. A similar number of nymphs of each cohort, 69 fed on hens (34.5%) and 68 fed on rabbits (34%), completed the cycle. No significantly (P > 0.05) differences were recorded among the average times from NI to adult in the cohort fed on hens (196.8 ± 15.8 days) and the average time in the cohort fed on rabbits (189.5 ± 22.9). The average span in days for each stage fed on hens was not significantly different to the average span for each stage fed on rabbits. The number of blood meals at each nymphal stage varied from 1 to 6 in both cohorts. The mortality rates were higher on fifth nymphal stage, in both cohorts. No significant (P > 0.05) differences were recorded on mortality rates on most nymphal stages of both cohorts. The average number of eggs laid per female from the cohort fed on hens in a 9-month period was 791.1, whereas the average number of eggs in the cohort fed on rabbits was 928.3.

Triatoma rubrovaria (Blanchard, 1843) (Hemiptera-Reduviidae-Triatominae) III: patterns of feeding, defecation and resistance to starvation

Data from the Chagas Disease Control Program indicate a growing domiciliary and peridomiciliary invasion of Triatoma rubrovaria in the State of Rio Grande do Sul, where it has become the most frequent triatomine species captured there since the control of T. infestans. Bionomic characteristics that could influence the vectorial capacity of T. rubrovaria as vector of Trypanosoma cruzi were evaluated: patterns of (i) feeding, (ii) defecation, and (iii) resistance to starvation, using insects fed on mice. Fifty three percent of the females showed a defecation pattern conducive to chagasic transmission, defecating either on or near the bite site. The averages of the resistance to starvation varied from 48.1 to 179 days, for the first and fifth nymphal stages, respectively. Our study shows that with respect to the patterns of feeding, defecation and resistance to fasting, T. rubrovaria presented similar rates to the ones observed for other effective vector species, such as T. infestans. Thus, based on our studies we conclude that T. rubrovaria has biological characteristics that can positively influence its capacity to become infected and transmit T. cruzi, and also to keep residual populations after chemical control interventions.

Crossing experiments detect genetic incompatibility among populations of Triatoma brasiliensis Neiva, 1911 (Heteroptera, Reduviidae, Triatominae)

Triatoma brasiliensis is composed of at least four geographic populations (brasiliensis, melanica, macromelasoma, and juazeiro) that have distinct chromatic, morphologic, biologic and ecologic patterns, and genetic composition. Reciprocal crosses between all pairwise combinations were carried out in order to evaluate the genetic and reproductive compatibility of these four populations. The F1 individuals developed normally and the resulting adults were crossed again to test the F2 and F3 viability. Genetic incompatibility was found between melanica and brasiliensis populations.

Glandular areas associated with the male genitalia in Triatoma rubrofasciata (Triatominae, Reduviidae, Hemiptera) and other Reduviidae

In this paper, glandular areas associated with the phallus in Triatoma rubrofasciata are described and illustrated for the first time. The glandular areas lie in the membrane surrounding the articulatory apparatus. In order to unambiguously define the locality of the respective glandular areas, some features of the pygophore-phallus connection are redescribed. A possible functional context of the gland secretions is discussed. A preliminary study of several other Reduviidae implies that the described glandular areas occur in a wider range of taxa in this group.

Feeding, defecation, and development times of Meccus longipennis Usinger, 1939 (Hemiptera: Reduviidae: Triatominae) under laboratory conditions

Aspects related to hatching, time-lapse between presenting the blood-meal and beginning of feeding, feeding time, postfeed defecation delay, mortality, and fecundity for each stage of Meccus longipennis life-cycle were evaluated. The bugs were maintained in a dark incubator at 27 ± 1ºC and 80 ± 5% rh, were fed weekly and checked daily for ecdysis or death. The hatching rate observed for 300 eggs was 76.7% and the average time of hatching was 19.8 days. Mean time-lapse between presentation of the blood meal and the beginning of feeding was under 5 min in nymphal stages and postfeed defecation delay was under 10 min in most stages, except in fourth and fifth stages. Mean feeding time was longer than 10 min in most stages, except in fourth stage. One hundred thirty-one nymphs (N) (65.5%) completed the cycle and the average time from NI to adult was 192.6 ± 34.8 days. The average span in days for each stage was 18.1 for NI, 21.4 for NII, 29.5 for NIII, 45.5 for NIV and 55.9 for NV. The number of bloodmeals at each nymphal stage varied from 1 to 5. The mortality rate was 3.29 for NI, 6.8 for NII, 2.92 for NIII 3.76 for NIV, and 10.16 for NV nymphs. The average number of eggs laid per female in a 9-month period was 615.6. Based on our results, we conclude that M. longipennis has some biological and behavioral characteristics which influence its capacity of becoming infected and transmitting Trypanosoma cruzi to human populations in those areas of Mexico where it is currently present.

Estudo morfométrico do gênero Panstrongylus Berg, 1879 (Hemiptera, Reduviidae, Triatominae)

The subfamily Triatominae is actually represented by 137 species distributed among 6 tribes and 19 genera. Within this subfamily, the genus Panstrongylus, Berg 1879, is composed by 13 species widespread in sylvatic, peridomestic, and domestic habitats of Neotropical regions. These species are vectors of Chagas disease and consequently are found associated with its main hosts, such as birds and mammals. Interest in species of this genus has been increasing in the last few years. Reports of several authors indicate these Triatominae to invade and colonize houses, increasing their epidemiological significance. Morphometry was used in this study to investigate correlations among possible closely related species. We measured 224 specimens among 13 species through a set of metric variables of the head. The results indicated that the genus Panstrongylus seems to be homogeneous since 10 of the 14 species were shown to be closely related.

Preliminary results of random amplification of polymorphic DNA among Triatominae of the phyllosoma complex (Hemiptera, Reduviidae)

In Mexico, Triatoma longipennis (Usinger), Triatoma picturata (Usinger), and Triatoma pallidipennis (Stal), primary Chagas disease vector species of the phyllosoma complex, were analyzed by randomly amplified polymorphic DNA (RAPD). Sixteen decametric primers resolved individual profiles not identical, but partially discriminative between species. Analysis based on pairwise presence/absence comparisons between the three species was performed using three primers and two outgroup species Triatoma infestans (Klug) and Triatoma barberi (Usinger). Fifty-three bands in total were scored, although only two bands were constant among the three phyllosoma complex species. Two other bands were constant only for T. longipennis and T. picturata together, and not present in T. pallidipennis. Neighbor Joining tree and the multiple correspondence analysis discriminated T. pallidipennis clearly from the other two species, although there was overlap between T. longipennis and T. picturata. The results indicate a close relationship between the studied species and support the hypothesis of their recent evolution. The suitability of RAPD to discern populations within the species is discussed.

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.

Feeding sources and natural infection of Belminus herreri (Hemiptera, Reduviidae, Triatominae) from dwellings in Cesar, Colombia

Belminus herreri, originally described from specimens collected in Panama, was considered entirely silvatic until to 2000 when it was found for the first time in a domestic habitat in Colombia. In 2001, during a new search of houses in the Department of Cesar, Colombia, 121 specimens were collected. Study of their feeding sources using an ELISA test revealed that 96% of these specimens had fed on cockroaches (Blattidae). However, a small proportion of these B. herreri specimens also showed the presence of Trypanosoma cruzi in their gut contents, suggesting a possible role for these insects in the epidemiology of Chagas disease.

Ciclo biológico em laboratório de Rhodnius brethesi Matta, 1919 (Hemiptera, Reduviidae, Triatominae), potencial vetor silvestre da doença de Chagas na Amazônia

R. brethesi is a sylvatic species from the Amazon region; it has been incriminated as responsible for the transmission of Chagas disease in collectors of piaçaba in this region. The aim of present study was to investigate the efficiency of these insects as potential vectors of Trypanosoma cruzi. Aspects related with feeding and defecation patterns, life time, and mortality had been observed in each instar of R. brethesi. We use 5th instar nymphs to get adults virgins, after the moulting 3 groups with 6 females and 2 males each were created to obtain eggs. After hatching, 1st instar nymphs had been weighed and kept in bottles until the next moult. Insects were fed once a week in mice. Results showed that the average period of incubation was 17 days, the number of blood meal was increasing from the 1st to the 5th instar nymph with 7 (average) to become adult, a significative numbers of the defecations occurring immediately after the bloodmeals. The total percentual of mortality was 16%. This results suggests that this species presents a good exploitation of blood meals and a brief nymphal development in laboratory conditions reflecting its behavior in sylvatic environments.

Triatoma rubrovaria (Blanchard, 1843) (Hemiptera - Reduviidae - Triatominae) IV: bionomic aspects on the vector capacity of nymphs

Triatoma rubrovaria has become the most frequently captured triatomine species since the control of T. infestans in the state of Rio Grande do Sul (RS), Brazil. The aim of this study was to evaluate aspects of the vectorial competence of T. rubrovaria using nymphs raised in laboratory under environmental conditions of temperature and humidity and fed on mice. The average developmental period of T. rubrovaria was 180.1 days. The percentage of defecation shortly after feeding was still higher than previous studies in which samples of T. rubrovaria subjected to a slight starvation period before the blood meal were used. The obtained results support former indication that T. rubrovaria presents bionomic characteristics propitious to be a good vector of Trypanosoma cruzi to man. Therefore its domiciliary invasion process must be continuously monitored.

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.

Morphometric analysis of Triatoma dimidiata populations (Reduviidae:Triatominae) from Mexico and Northern Guatemala

Triatoma dimidiata is one of the major vectors of Chagas disease in Latin America. Its range includes Mexico, all countries of Central America, Colombia, and Ecuador. In light of recent genetic analysis suggesting that the possible origin of this species is the Yucatan peninsula, we have analyzed populations from the state of Yucatan, San Luis Potosi, and Veracruz in Mexico, and a population from the southern region of the Yucatan peninsula located in Northern Guatemala, the region of El Peten. Classical morphometry including principal component, discriminant, sexual dimorphism, and wing asymmetry was analyzed. San Luis Potosi and Veracruz populations were indistinguishable while clearly separate from Yucatan and Peten populations. Despite important genetic differences, Yucatan and Peten populations were highly similar. Yucatan specimens were the smallest in size, while females were larger than males in all populations. Only head characters were necessary to distinguish population level differences, although wing fluctuating asymmetry was present in all populations. These results are discussed in light of recent findings suggesting genetic polymorphism in most populations of Triatoma dimidiata south of Chiapas to Ecuador.

Morfologia comparada dos ovos e ninfas de Triatoma vandae Carcavallo, Jurberg, Rocha, Galvão, Noireau & Lent, 2002 e Triatoma williami Galvão, Souza & Lima, 1965 (Hemiptera, Reduviidae, Triatominae)

Eggs and all nymphs of these species were studied employing light microscopy (LM) and scanning electron microscopy (SEM). The major differences observed by LM in the eggs were related to the presence and the distribution of pores on the surface of their chorion. Morphological differences among three nymphal stages (1st, 3rd, and 5th) development of each species were observed. The differential characteristics are chromatic and in the shape of connexival spots. The ultrastructure of the ventral region of the head and the IX, X, and XI abdominal segments (anal tube) of the both species were described demonstrating morphological differences that can be used for diagnosis of the species.

A micro-spreading improvement for spermatogenic chromosomes from Triatominae (Hemiptera-Reduviidae)

Cytogenetics of triatomines have been a valuable biological tool for the study of evolution, taxonomy, and epidemiology of these vectors of Trypanosoma cruzi. Here we present a single microtube protocol that combines micro-centrifugation and micro-spreading, allowing high quality cytogenetic preparations from male gonadal material of Rhodnius prolixus and Triatoma lecticularia. The amount of cellular scattering can be modulated, which can be useful if small aggregates of synchronous cells are desired. Moreover, a higher number of slides per gonad can be obtained with fully flattened clean chromosomal spreads with minimum overlaps, optimal for classical and modern molecular cytogenetic analyses.