Activity and shelter-related behavior in Rhodnius prolixus: The role of host odours.

Triatomine bugs are considered nocturnal insects that feed on the blood of vertebrates and remain hidden inside narrow shelters during daylight hours. Nevertheless, it is not clear whether these insects become active and leave their shelters on a daily basis, less frequently or, even fortnightly. Activity patterns were studied in Rhodnius prolixus Stål, 1859 (Hemiptera: Triatominae) associated with shelters to evaluate whether the decision to leave a shelter depends on bug starvation and the presence of host odours. Experiments were conducted with groups of 5th instar nymphs released in an experimental arena offering an artificial shelter consisting of a piece of corrugated cardboard positioned in its centre. Results indicate that host odours promoted a significant increase in shelter related activity, i.e. shelter-leaving or entering movements, and also in bug locomotion. This increase could only be observed with bugs starved for 30 or 60 days, but not for 21 days. Most R. prolixus nymphs that left shelters and engaged in locomotory activity were starved and in the presence of host odours. Even though R. prolixus is mostly considered a very active and "aggressive" triatomine, our results contradict this perspective and suggest that its main strategy regarding hosts is to wait and carefully evaluate feeding chances before becoming exposed. This behavioural strategy might have arisen through their evolution in palm trees in association with a diverse fauna that may impose predation risks.

[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.

[Biological potential of Triatoma brasiliensis]. / Potencial biológico do Triatoma brasiliensis.

Biological and physiological parameters of Triatoma brasiliensis, Triatoma infestans, and Triatoma pseudomaculata were studied and compared. T. brasiliensis, reared on mice, showed a faster evolutionary cycle from first stage to adult and higher fecundity, when compared to the other species. T. infestans showed the fastest blood intake in both hosts tested, followed by T. brasiliensis and T. pseudomaculata. Clotting tests using salivary gland extracts of T. brasiliensis presented intermediary values of anti-clotting activity when compared to T. infestans and T. pseudomaculata.

Elimination of bancroftian filariasis (Wuchereria bancrofti) in Santa Catarina state, Brazil.

During the 1950s, three foci of Wuchereria bancrofti transmission were identified in the State of Santa Catarina, Brazil. In Florianópolis, São José da Ponta Grossa and Barra da Laguna community treatment of bancroftian filariasis with diethylcarbamazine (DEC) was performed using two distinct approaches, without vector control or improvements in sanitation. In two of the three communities only microfilaraemic individuals were treated, while in Barra da Laguna the entire population received DEC treatment regardless of their infection status. In both cases, transmission of the parasite was blocked and no new cases were detected in all localities for up to 10 years. Recently, a new survey in São José da Ponta Grossa and Barra communities revealed no microfilaria-positive individuals, including residents that were positive in the 1950s. These data confirm that transmission of W. bancrofti was interrupted in Santa Catarina, and mass treatment appears to be more effective than treatment of microfilaraemic individuals only.

Influence of the blood meal source on the development of Triatoma infestans, Triatoma brasiliensis, Triatoma sordida, and Triatoma pseudomaculata (Heteroptera, Reduviidae).

The objective of this study was to determine the influence of the blood meal source on the life cycle and reproductive development of female Triatoma infestans (Klug, 1834), Triatoma brasiliensis Neiva, 1911, Triatoma sordida (Stal, 1859), and Triatoma pseudomaculata Corrga & Espfinola, 1964. In all triatomine species studied the life cycle was shorter for the groups fed on mice than for those fed on pigeons, the range of differences being between 1.5 times (T pseudomaculata and T. infestans) and 2.4 times (T brasiliensis). The mortality rate of nymphs during the life cycle tended to be greater in insects fed on pigeons than in those fed on mice, the differences for T. brasiliensis being statistically significant. Females of T sordida and T pseudomaculata had a greater fecundity than those of T. infestans and T. brasiliensis independently of the blood meal source. The differences of fecundity observed probably reflect differences in the availability of blood in the silvatic ecotopes of these species, meals being more frequent for T. infestans and T brasiliensis, which live at high densities in association with rodents in highly stable ecotopes. Because T. sordida and T. pseudomaculata live in more unstable ecotopes with fewer sources of blood they form small sparse colonies and invest more energy in reproduction than maintenance.

Characterization of Trypanosoma rangeli strains isolated in Central and South America: an overview.

Trypanosoma rangeli is a hemoflagelate parasite that infects domestic and sylvatic animals, as well as man, in Central and South America. T. rangeli has an overlapping distribution with T. cruzi, the etiological agent of Chagas disease, sharing several animal reservoirs and triatomine vectors. We have isolated T. rangeli strains in the State of Santa Catarina, in southern Brazil, which dramatically increased the distribution area of this parasite. This brief review summarizes several studies comparing T. rangeli strains isolated in Santa Catarina with others isolated in Colombia, Honduras and Venezuela. The different methods used include indirect immunofluorescence and western blot assays, lectin agglutination, isoenzyme electrophoresis and random amplified polymorphic DNA analysis, triatomine susceptibility, in vitro cell infection assays, and mini-exon gene analysis.

Population biology of Rhodnius domesticus Neiva & Pinto, 1923 (Hemiptera: Reduviidae) under laboratory conditions.

The entire life cycle of Rhodnius domesticus, fed weekly on mice, was studied under controlled conditions. Aspects related to hatching, life time, mortality, feeding behaviour and fecundity for each stage of the insect life-cycle were evaluated. The hatching rate observed in 100 eggs was 57% and the mean time of hatching was 15.6 days. Forty-six nymphs (80.7%) completed the cycle and the mean time from NI to adult was 93.8 days. The average span in days for each stage was 12.4 for NI, 9.8 for NII, 14.2 for NIII, 16.8 for NIV and 25.0 NV. the number of bloodmeals in each nymphal stage varied from 1 to 3. The mortality rate was 12.3% for NI, 3.5% for NII and 1.7% for NIII and NV nymphs. The mean number of eggs laid per female in a 9-month period was 333.1. Average adult survival rates were 287.6 + 133 and 328 + 73 days for males and females respectively.