Enzyme polymorphism in triatomine bugs of the genus Rhodnius (Hemiptera: Reduviidae), vectors of Chagas disease, is analysed using both starch and polyacrylamide gel electrophoresis. Out of forty-five enzymes assayed, the electromorphs of seventeen of them: AO, CA, DIA, ES, ES-A, FH, GPD, G6PD, GPI, MDH, ME, 6PGD, PGM, ACON, ACPH, LAP and SOD, involving twenty-two putative structural loci, were scorable. These gene-enzyme systems were therefore selected for routine characterization of R.prolixus Stal adults from different strains. The first thirteen enzymes, involving sixteen structural loci, were also analysed in first instar nymphs of the three species, R.prolixus, R.robustus Larrousse and R.pictipes Stal. Allelic frequencies were calculated for three R.prolixus strains: three to five loci appeared to be polymorphic. The proportion of polymorphic loci (22%) and the average heterozygosity (0.06) indicated low genetic variability, with significant differences between the strains at individual loci. Rhodnius prolixus and R.robustus were found to have identical isozymic patterns. R.pictipes was genetically well differentiated, with twelve diagnostic loci.

A statistical evaluation of the population dynamics of Panstrongylus geniculatus is based on a cohort experiment conducted under controlled laboratory conditions. Animals were fed on hen every 15 days. Egg incubation took 21 days; mean duration of 1st, 2nd, 3rd, 4th, and 5th instar nymphs was 25, 30, 58, 62, and 67 days, respectively; mean Panstrongylus geniculatus (Latreille 1811), is widely distributed in America; it is found from southern Mexico to northern Argentina. It has epidemiological importance since it has been found naturally infected with Trypanosoma cruzi from the beginning of this century (Chagas 1912).In Venezuela, it has been captured in many states (Ramírez Pérez 1987). Pifano (1986) studying the urban Chagas' disease in the valley of Caracas reported individuals of P. geniculatus in human dwellings, apparently associated to the marsupial Didelphis marsupialis.It is attracted by light and has been collected in human dwellings, but it does not colonize them (Miles et al. 1981); it is a sylvatic species (Lent & Wygodzinsky 1979, Zeledón 1983.It has been little studied because of the difficulties for rearing and maintenance, and for the low number of collected specimens (Miles et al. 1981, Ramírez Pérez 1987; therefore, very little literature has been published on its biology, ecology and epidemiology. Barreto (1967) studied some ecological aspects and indicated a close association with some mammals like armadillo. Lent and Jurberg (1969) Here we present the results of a study of P. geniculatus fed only on hen, under controlled constant environmental conditions, with special emphasis on its demographic characteristics, in order to contribute to the kwowledge of the population dynamics of this species. MATERIALS AND METHODSThe population of P. geniculatus used in this experiment was obtained from a colony founded by a single female collected in a human dwelling in the area of San Jacinto, located in the city of Trujillo, Trujillo State, Venezuela. The colony was kept in a climatic chamber at 26±3°C and 90±10% RH, and fed on hens.Vital statistics described in this study were based on a cohort constituted by 63 recently laid eggs (0 to 48 hr old); these were kept in 150 cm 3 glass containers until all viable eggs hatched; then, all 1st instar nymphs were transferred to a 3,785 l broad mouth jar, covered with nylon mesh and provided with vertically placed strips of paper in order to allow insects to climb to the jar top at feeding time and provide them resting places and serve as laying sites.

External Morphology of Triatoma rickmani Zeledón & Ponce, 1972 by Scanning Electron Microscopy -A male of Triatoma ryckmani Zeledón & Ponce, 1972, was studied by scanning electron microscopy. Only few specimens of this species are known. In this paper, some structures from the head, thorax, abdomen and distal region of the second leg are shown. Some of them could have taxonomic importance, as the oculo-ocellar region, the buccula, the anterolateral angle of the collar, the scutellum with the process longer than the main body, the stridulatory sulcus with an unusual backward vermiform area, and the tibia-tarsal articulation, with a spongy fossula. The last structure was absent in specimens previously studied (Lent & Wygodzinsky 1979). Differences between this specimen and others previously described by several authors are dicussed.

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