Algunos de los parámetros reproductivos fueron medidos en 60 hembras adultas de Marmosa xerophila para inferir el significado de algunas de sus adaptaciones a ecosistemas semiáridos cuando se comparan con aquéllas de M. robinsoni, una especie presente en sistemas más húmedos y a la que está estrechamente relacionada filogenéticamente. El estudio se llevó a cabo en un arbustal seco espinoso en la Península de Paraguaná, Estado Falcón, Venezuela. Los datos de campo se colectaron a través de dos métodos: captura-marcado-recaptura y marcado con radioisótopos. Un pico reproductivo se presentó en la estación seca, entre junio y julio. Las hembras con señales de haber destetado sus crías eran más evidentes entre julio y febrero. No se observó actividad reproductiva en las hembras entre marzo y mayo. El ciclo reproductivo duró 60 días y el tamaño promedio de la camada fue 7,9 crías. La estrategia reproductiva de M. xerophila es similar a la de M. robinsoni que habita selvas tropicales, lo que refleja una gran plasticidad que permite a estas especies adaptarse exitosamente a diferentes ecosistemas neotropicales.

Some reproductive parameters were measured in 60 adult females of Marmosa xerophila to infer the significance of some adaptations to a semi-arid ecosystem when compared to M. robinsoni, a filogenetically closely related species inhabiting more humid environments. The study was carried out in a tropical thorny woodland in the Peninsula of Paraguaná, Falcon State, Venezuela. Field data were collected by two methods: capture-mark-recapture and radioactive tagging. A reproductive peak occurred in June and July, during the dry season. Post-lactating females were detected from July to February. There was no reproductive activity from March to May. The rearing cycle lasted 60 days and the mean litter size was 7.9 young. The reproductive strategy of M. xerophila is similar to the rainforest species M. robinsoni, reflecting a great plasticity that allows Marmosa species to adapt successfully to different Neotropical ecosystems

Foram medidos alguns parâmetros reprodutivos de 60 fêmeas adultas de M. xerophila para inferir sobre o quão significativas são algumas adaptações ao ecossistema semi-árido comparando-os com M. robinsoni. O estudo foi realizado em um bosque espinhoso tropical na Península de Paraguaná, Estado Falcon, Venezuela. Os dados de campo foram coletados usando-se dois métodos: captura-marcação-recaptura e uso de etiquetas radioativa. Um pico de reprodução ocorreu em junho e julho, durante a estação seca. Fêmeas pós-lactantes foram detectadas de julho a fevereiro. Não houve atividades reprodutivas de março a maio. O ciclo de criação dura 60 dias e o tamanho médio da ninhada foi de 7,9 jovems. A estratégia reprodutiva de M. xerophila é similar a de M. robinsoni de floresta tropical, refletindo uma grande plasticidade que permite às espécies do gênero se adaptarem com êxito em diferentes ecossistemas Neotropicais.

Se analizó la dinámica poblacional de las pequeñas ratas silvestres del arroz Microryzomys minutus en ambientes alterados y primarios, en un bosque nublado de los Andes venezolanos. El estudio fue basado en 121 animales (66♀♀ y 55♂♂ ) recolectados entre 1995 y 1998, usando trampas que contenían formalina. Esta especie está presente en ambos hábitats lo que confirma su amplia tolerancia ecológica. La abundancia poblacional fue mayor en ambientes alterados que en los no alterados. M. minutus presenta dimorfismo sexual en el peso: los machos son más pesados que las hembras.

The population dynamics of the small forest rice rat Microryzomys minutus, a murid rodent that occurs in the high altitudes of the northern and central Andes, was studied in disturbed and primary environments in a cloud forest of the Venezuelan Andes (Juan Pablo Peñaloza National Park, 8º11’N, 71º49’W). We collected 121 animals (66♀♀ and 55♂♂ ) between 1995 and 1998, using pitfall traps with formalin. Adult males were heavier than adult females. Relative abundance was much greater in the disturbed environments (over 10 individuals in some periods) than in the primary cloud forest: 4-8 individuals. In the disturbed environments, the rats were extremely abundant in the first sampling period, and less frequent afterwards. In the cropland, abundance showed some fluctuations during the study and displayed two small abundance peaks in March-June 1997 and 1998. In the mined area, the rats had irregular fluctuations until March-June 1997 and were not recorded in July-October 1997. The occurrence of this rat in both disturbed and natural habitats confirms the wide ecological tolerance of this species. Rev. Biol. Trop. 54(2): 651-. Epub 2006 Jun 01.

The complete life cycle of Triatoma flavida, weekly fed on hens, was studied at 28±2°C and 80±10% RH. Aspects related to hatching, life span, mortality and feeding behavior for each stage of its life cycle were evaluated. The hatching rate observed for 100 eggs was 93% with an average incubation period of 27.2 days. Sixty-two nymphs completed the cycle and the mean egg to adult development time was 230.4 days. Mean duration of 1st, 2nd, 3rd, 4th and 5th instar nymphs was 22.1, 25.3, 36.7, 49.7 and 69.4 days, respectively. The number of blood meals on each nymphal stage varied from 1 to 7. The mortality rate was 6.5% for NI, 23% for NIII and 7.5% for NV nymphs. Mean number of laid eggs per female was 283.1. Adult survival rates were 344.8 ± 256.4 days for males and 285.3 ± 201.8 days for females.

The period of resistance to starvation and the loss of weight until death of Rhodnius neivai in all stages of development were studied. Work was based on experiments conducted under controlled laboratory conditions. One hundred specimens of each nymphal instar were observed: 50 were fed on chicken and 50 on rabbit. Adult females and males were kept together and fed on each host. All bugs were weighed weekly until death. Laid eggs were collected weekly and observed during five weeks to obtain hatchability. Resistance to starvation was similar with both hosts and increased with the evolutionary stage, excepting the 5th nymphal instar and adults. With both hosts, loss of weight was abrupt in the first week and steady in the following weeks. In adults, on the first weeks after eating, there was little or no mortality, after which mortality increased rapidly with the starving time. Reproductive output was higher in the bugs fed on rabbit. R. neivai is among the least resistant triatomine species.

Changes in life tables of Rhodnius neivai due to variations of environmental temperature were studied, based on nine cohorts. Three cohorts were kept at 22°C, three at 27°C and three at 32°C. Cohorts were censused daily during nymphal instars and weekly in adults. Nine complete horizontal life tables were built. A high negative correlation between temperature and age at first laying was registered (r=-0,84). Age at maximum reproduction was significantly lower at 32°C. Average number of eggs/female/week and total eggs/female on its life time were significantly lower at 22°C. Total number of egg by cohort and total number of reproductive weeks were significantly higher at 27°C. At 32°C, generational time was significantly lower. At 27°C net reproductive rate and total reproductive value were significantly higher. At 22°C, intrinsic growth, finite growth and finite birth rates were significantly lower. At 22°C, death instantaneous rate was significantly higher.

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 nymphal development time was 39 weeks and adult longevity was 72 weeks. Females reproduced during 30 weeks, producing an average of 61.6 eggs for female on its lifetime; the average number of eggs/female/week was 2.1. Total number of eggs produced by the cohort was 1379. Average hatch for the cohort was 88.9%; it was not affected by age of the mother. Age specific survival and reproduction tables were constructed. The following population parameters were evaluated, generation time was 36.1 weeks; net reproduction rate was 89.4; intrinsic rate of natural increase was 0.125; instantaneous birth and death rates were 0.163 and 0.039 respectively; finite rate of increase was 1.13; total reproductive value was 1196 and stable age distribution was 31.2% eggs, 64.7% nymphs and 4.1% adults. Finally the population characteristics of P. geniculatus lead to the conclusion that this species is a K strategist.