[The effect of the period of egg quiescence on the life cycle of Aedes aegypti (Linnaeus, 1762) (Diptera, Culicidae) under laboratory conditions]. / Influência do período de quiescência dos ovos sobre o ciclo de vida de Aedes aegypti (Linnaeus, 1762) (Diptera, Culicidae) em condições de laboratório.

The influence of the period of egg quiescence on the life cycle of Aedes aegypti (Linnaeus, 1762) (Diptera, Culicidae) was studied under laboratory conditions in order to improve the management of vector control. The eggs are known to be the most resistant stages during development, allowing a long survival of the mosquitoes under unfavorable climatic conditions. The experiments were performed in a biological chamber kept at 28 +/- 1 degrees C temperature, with 80 +/- 5% relative humidity and 12 hours of photophase. Data about the influence of different periods of quiescence on eclosion, larval and pupal development and the developmental cycle are presented. We observed a highly significant effect of the period of quiescence on larval eclosion. The period of quiescence had no influence on the duration of larval or pupal incubation. Eggs originating from the same period of quiescence showed significantly different periods of incubation. The larvae emerged in groups defined by the period of incubation. This group effect was significant during the cycle. In 99.8% of the cycles the variation was determined by incubation.

Evaluation of risk factors for house infestation by Triatoma infestans in Brazil.

An active entomologic survey was conducted by a team of trained health workers in a rural area endemic for Chagas' disease in central Brazil. They used pyrethrum as a flushing agent and 4,232 houses were inspected for triatomine bugs both inside and in the immediate environs. Houses with Triatoma infestans or evidence of an established colony were identified and defined as infested houses (cases). The building and environmental characteristics of 161 randomly selected infested houses were compared with 161 matched, noninfested houses (controls) that were the shortest distance from the infested house. Domestic and peridomestic potential risk factors associated with house infestation by Triatoma infestans were assessed by logistic regression analysis. Incomplete house construction (odds ratio [OR] = 2.5, 95% confidence interval [CI] = 1.5-4.1) was confirmed as a risk factor related to the presence or evidence of Triatoma infestans in the dwellings. The study also disclosed a statistically significant association between the presence of rats (OR = 1.6, 95% CI = 1.1-2.6) and indoor crop storage (OR = 2.3, 95% CI = 1.1-5.2) and house infestation. Further experimental field studies using tagged rodents should be conducted to assess their epidemiologic role in the domestic chain of Trypanosoma cruzi transmission.

[A comparative study between natural and artificial xenodiagnosis in chronic Chagas' disease patients]. / Estudo comparativo entre o xenodiagnóstico natural e o artificial, em chagásicos crônicos.

In order to study the sensitivity of the xenodiagnosis technique a comparison between natural and artificial xenodiagnosis methods was performed in 57 chronic phase chagasic patients (31 female), with ages ranging from 26 to 83 years. All patients had demonstrable antibodies against Trypanosoma cruzi. Forty first instar nymphs of Dipetalogaster maximus were used for each of both methods and for each patient. The positivity of xenodiagnosis artificial was significantly higher than the routine test method. These results did show that a single application of 40 bugs by the artificial method yielded a similar result than 3 applications of 40 bugs each, by the natural method. The positivity of xenodiagnosis was significantly higher in patients between 56-65 and 66-83 years old than at other ages. Males were predominant in this age group. These results showed the viability of artificial xenodiagnosis and its use in routine laboratory testing.

[Importance of the method for obtaining feces from triatominae in the assessment of triatomine susceptibility to Trypanosoma cruzi]. / Importância do método de obtenção das dejeções dos triatomíneos na avaliação da suscetibilidade triatomínica para Trypanosoma cruzi.

Two patients on the acute phase of Chagas' disease were submitted to xenodiagnosis examination with different species of triatomine bugs, in order to study bug susceptibility to Trypanosoma cruzi. Species used were Dipetalogaster maximus, Rhodnius neglectus, R. prolixus, R. robustus, Triatoma infestans and T. rubrovaria. Both the number of infected bugs, and the number of excreted trypanosomes by bug, were used as parameters for evaluation of species susceptibility. Xenodiagnosis reading was performed by two methods, the classic abdominal compression and the spontaneous dejection method; this was more efficient than the former in relation to the number of parasites per wet smear (by Wilcoxon test). When susceptibility was evaluated by the number of infected bugs, in one of the patients all D. maximus and R. neglectus became infected (100%), 95% of R. robustus, 90% of R. prolixus and T. rubrovaria, and 85% of T. infestans. When evaluation was performed through the number of excreted parasites in this patient with reading by abdominal compression, the higher susceptibility was with R. neglectus, followed by R. prolixus, D. maximus and R. robustus, T. infestans and T. rubrovaria; reading by spontaneous dejection yielded better results for D. maximus and R. prolixus followed by T. rubrovaria, R. robustus, T. infestans and R. neglectus. For the other patient susceptibility evaluated by the number of excreted parasites was similar by both reading methods and did show the same susceptibility pattern (R. neglectus and then T. rubrovaria and T. infestans), but the number of excreted trypanosomes was much higher by the spontaneous dejection method.

[The influence of temperature on the biology of triatominae. IX. Rhodnius nasutus Stal, 1859 (Hemiptera, Reduviidae)]. / Influência da temperatura na biologia de triatomíneos. IX. Rhodnius nasutus Stal, 1859 (Hemiptera, Reduviidae).

The influence of temperature on the biology of Rhodnius nasutus Stal, 1859 (Hemiptera, Reduviidae) was studied in order to obtain a larger number of triatominae reared in laboratory to use in xenodiagnosis and to be able to get information for their proper control. The experiments were performed in two climatized chambers at 25 +/- 0.5 degrees C and 30 +/- 1 degrees C, 70 +/- 5% of relative humidity and photoperiod of 12 hours. Data in relation to evolution cycle, period between emergency of adults and first oviposition, fecundity, fertility, amount of blood ingested and fast resistance, are presented. The mean duration of the evolutive cycle for males and females was 145.7 days at 25 degrees C and 114.2 days at 30 degrees C. The mean of blood ingested to complete the evolutive cycle was 304.3 mg and 350.3 mg, at 25 degrees C and 30 degrees C, respectively. The triatominae survival on conditions of absolute fast was significantly higher at 25 degrees C than at 30 degrees C (P less than 0.01).