Head morphometry and isoenzymatic profile of two Triatoma infestans Klug, 1834 (Hemiptera, Reduviidae) populations.

The triatomine bug Triatoma infestans was probably originated in Bolivia and dispersed passively over large areas of South America, where it is the major vector of Trypanosoma cruzi. In its probable origin area this species shows two different patterns of behaviour, being found both in sylvatic and human related habitats. Such behaviour is not observed in other areas of its distribution, where it is exclusive to human related habitats. The main objective of the present study was to evaluate head morphometry characters and isoenzymes patterns of two T. infestans populations, one collected in Minas Gerais (Brazil) and other in the Cochabamba Valley (Bolivia), in order to elucidate the factors that could have an implication with the different colonization behaviour. The two populations presented differences in both morphometric (head size) and isoenzymes (specially PGM enzyme profile). The insects from the colonies reared for several years in laboratory conditions, showed reduction in head size starting from the third generation, maintaining this same size in all generations after, until 10 years after generation. The laboratory rearing conditions could be similar to human associated habitats, inducing certain level of genetic homogeneity. Our results showed increase of genetic homogeneity in Brazilian and laboratory-reared colonies from Bolivia, that may be due to a selection process due to passive dispersion, followed by several founder effects episodes and genetic drift.

Dynamics of thermopreference in the Chagas disease vector Panstrongylus megistus (Hemiptera: Reduviidae).

The thermopreference of resting P. megistus (Burmeister, 1834) adults was studied in a temperature gradient. We also determined the thermopreference for oviposition and ecdysis. Thermopreference of resting individuals depended on the feeding state of the insects. Results demonstrated an initial resting preference of approximately 290 degrees C, which gradually changed to 26-27 degrees C with increasing starvation. A daily variation in thermopreference was also observed with this species. The insects showed a daily maximum preference at the beginning of the dark phase, and a minimum preference during the first half of the light phase. Ecdysis took place all along the gradient, but exhibited a maximum frequency at 30 degrees C. Most eggs were found between 25 and 29 degrees C. Results are discussed in relation to the ecology of P. megistus as compared with other related species, and the existence of mechanisms of behavioral thermoregulation in the group.

Aggregation behaviour in Panstrongylus megistus and Triatoma infestans: inter and intraspecific responses.

We tested the aggregation response to inter and intraspecific chemical signals in Panstrongylus megistus and Triatoma infestans. As previously described for T. infestans, larvae of P. megistus significantly aggregated on papers impregnated with their own excrement and on papers marked with cuticular substances deposited on surfaces on which these insects had walked. T. infestans bugs also aggregated on papers impregnated by faeces or by cuticular substances of P. megistus, and P. megistus aggregated on papers contaminated by faeces or by cuticular substances of T. infestans. The response of P. megistus to its cuticular substances was significantly stronger than that to its faeces. The non-specificity of the two signals is discussed in the context of the ecological relationship between both species.

Experimental evidence for a demographic cline in Panstrongylus megistus populations.

The population biology of three populations of Panstrongylus megistus was compared to determine possible influence on the behaviour and epidemiological importance of this species. The results demonstrated differences in terms of egg eclosion time, nymphal mortality and development rates, and feeding and defaecation rates. These differences appeared to follow a geographical cline, primarily reflecting different degrees of adaptation to domestic habitats.

[Operational aspects of Triatoma brasiliensis control]. / Aspectos operacionais do controle do Triatoma brasiliensis.

Vector control strategies against indigenous species is not easy, due to their capacity to reinvade treated premises from sylvatic ecotopes. Between August 1996 and December 1997 we conducted a study on reinfestation of houses after spraying in a county in the State of Ceará. Of 277 houses examined, 113 (40.8%) were infested (21.7% intradomiciliary and 35.4% peridomiciliary). Of the 433 Triatominae collected, 207 were Triatoma brasiliensis (49% of which intradomiciliary, with a mean of 1.8 insects/house) and 226 were Triatoma pseudomaculata (97% peridomiciliary). The age structure of the two indicated a univoltine development cycle for T. brasiliensis and two cycles per year for T. pseudomaculata. Four months after spraying with deltamethrin SC 25mg ia/m2, 9.7% of the houses were still positive, mainly with peridomestic infestations. Intradomiciliary wall bioassays showed persistence of the insecticide up to 9 months after spraying. Considering the high potential for recolonization of treated premises from sylvatic foci, we propose an operational strategy combining traditional evaluations and community-based surveillance with increased selective interventions and community education.

[Microclimatic properties of the Triatoma brasiliensis habitat]. / Aspectos microclimáticos del hábitat de Triatoma brasiliensis.

Vector-borne transmission of Chagas disease in Northeast Brazil is basically by Triatoma brasiliensis. It is thus crucial to determine this species' microclimatic preferences as limiting factors for its distribution and ability to infest domestic environments. We analyze the microclimatic properties of the shelters in which these insects are found in wild, domestic, and peridomiciliary environments in the State of Ceará, at Brazil. We measure temperature and relative humidity (RH) every 15 minutes for 3 days. Thermal variation was greatly dampened inside both domiciliary refuges and the more protected internal places in wild stony sites. For RH, we observed a similar dampening pattern, but mean RH was lower in both domiciliary refuges and wild ones inside stony sites as compared to reference levels in the surrounding environment. The results are discussed with regard to this species' microclimatic preferences in the laboratory and its potential as determinants of its geographical distribution.

Comparative developmental and susceptibility to insecticide of Bolivian and Brazilian populations of Triatoma infestans.

The triatomine bug Triatoma infestans probably originated in Bolivia and dispersed passively over wide areas of South America, where it is the principal vector of Trypanosoma cruzi. In the region of its probable origin this species shows colonization in two different ecotopes, so that it may be encountered in sylvatic as well as in artificial habitats. The sylvatic colonization pattern is not observed in the rest of its range, where T. infestans is exclusive to man-made habitats. The objective of this study was to compare several aspects of two T. infestans populations, one from Minas Gerais (Brazil) and the other from the Cochabamba Valley (Bolivia), with a view to elucidate the factors associated with the different colonization patterns observed for this species. The differences between the developmental cycle, weight, capacity to ingest blood and mortality rate of first instar nymphs should indicate more fragility of Brazilian population that may be related to its elimination possibility.

Performance of yeast-baited traps with Triatoma sordida, Triatoma brasiliensis, Triatoma pseudomaculata, and Panstrongylus megistus in laboratory assays.

The effectiveness of a trap for triatomines baited with yeast cultures has been previously demonstrated for Triatoma infestans in laboratory assays. We report here results from laboratory assays testing yeast traps for Triatoma sordida, Triatoma brasiliensis, Triatoma pseudomaculata, and Panstrongylus megistus. All assays were conducted in an open experimental arena 100 cm x 100 cm, with two traps placed at opposite sides of the arena. One of the traps contained a yeast culture, and the other trap contained a saccharose solution as a control. Two series of experiments were done, one without a refuge for the insects and one with a refuge. The results obtained clearly demonstrated that the yeast-baited traps were effective in the laboratory in capturing both T. sordida and P. megistus. For T. sordida, yeast-baited traps captured significantly more bugs than did the control traps (t test P value = 0.03). For P. megistus, when a refuge was provided during the assay, yeast-baited traps also captured significantly more bugs than did the control traps (t test P value = 0.006). In the experiments with T. brasiliensis and T. pseudomaculata, both traps captured some insects, but the yeast traps captured many fewer bugs than was true with the T. sordida and P. megistus bugs. These results indicate that, in the laboratory, yeast traps can capture considerable numbers of T. sordida and P. megistus in one night. We discuss the potential use of yeast traps for detecting and capturing both triatomine species.

Yeast culture volatiles as attractants for Rhodnius prolixus: electroantennogram responses and captures in yeast-baited traps.

Responses to air currents carrying volatiles from yeast cultures were measured by means of electroantennograms (EAGs) in the haematophagous bug Rhodnius prolixus and we tested yeast-baited traps in the laboratory. The volatiles liberated by yeast cultures generated a clear electrophysiological response, much higher than that obtained during stimulation with clean air. The addition of yeast cultures to the traps dramatically increased overnight capture. A modification performed on the traps was effective for this species, as the bugs were immobilised once they fell into the device. Our results demonstrate that yeast culture volatiles are attractive for R. prolixus. The results obtained by means of electroantennogram techniques represent the first electrophysiological evidence of the perception of yeast volatiles by the antennae of a triatomine bug. We discuss the relevance of our results in view of currently used sampling techniques and control strategies.

Variations of the external male genitalia in three populations of Triatoma infestans Klug, 1834.

Triatoma infestans is the triatomine that presents the greatest dispersion area in South America. However, it is not known whether the original characteristics of this insect remained in its long dispersion process. The purpose of this work was to study comparatively the external male genitalia of insects from different populations of T. infestans, two from Brazil (Minas Gerais and Bahia) and one from Bolivia (Cochabamba Valley), and to investigate the correlation between the morphological and behavioral variations. Differences were observed in one of the structures of the external genitalia (endosoma process) that could be used to characterize the insects from the three populations studied.

[Feeding and defecation dynamics of Triatoma sordida]. / Dinâmica da alimentação e dejeção do Triatoma sordida.

Today, Triatoma sordida is the most frequently captured triatomine in Brazil. For a better understanding of its vectorial potential, its feeding dynamics and dejections behaviour were studied in comparison with Triatoma infestans and P. megistus. The proportion of T. sordida and T. infestans that blood fed on anaesthetized rats did not differ significantly. There was no significant difference in the time elapse between release of the bugs and the initiation of blood feeding. The mean time between completion of a blood meal and the first dejection was significantly lower in T. infestans than in T. sordida. The numbers of insects that defecated during the blood meal or immediately afterwards was similar for both species. Approximately 80 specimens of each of T. sordida, T. infestans and Panstrongylus megistus were offered daily blood meals for 30 minutes, over a period of 30 days. T. sordida bit more frequently than did P. megistus and T. infestans. These data could indicate that T. sordida may not be completely adapted to its host and might have difficulty in complete its blood meal.