Population size regulation is density-dependent in Rhodnius prolixus (Hemiptera: Reduviidae) through an irritability mechanism

BACKGROUND Physical factors can determine the level of triatomine abundance, but do not regulate their population densities, and neither do natural enemies. OBJECTIVES To identify the processes associated with density-dependent triatomine population regulation. METHODS We set-up a laboratory experiment with four interconnected boxes; the central box harbored Rhodnius prolixus bugs and one hamster. Stage 5 and adult densities of 10, 20, 30, 40, and 60 bugs per hamster, were replicated four times (except the density of 60 bugs). Hamster's irritability and several triatomine responses were measured: feeding, development time and longevity, mortality, fecundity, dispersal, and the net reproductive value (R o ). FINDINGS Density had a statistically significant effect on irritability, but not on the percent of bugs feeding. Density was significant on blood meal size ingested in bugs that did not move between boxes, but not significant when the bugs moved. Density and irritability affected the proportion of stage 5 nymphs molting, and the proportion of adult bugs dying per day and over a three-week period. There was a highly significant effect of density and irritability on R o . MAIN CONCLUSIONS We showed that a density-dependent mechanism, acting through the irritability of the host, seems the most plausible process regulating populations in triatomines.

Large-scale patterns in morphological diversity and species assemblages in Neotropical Triatominae (Heteroptera: Reduviidae)

We analysed the spatial variation in morphological diversity (MDiv) and species richness (SR) for 91 species of Neotropical Triatominae to determine the ecological relationships between SR and MDiv and to explore the roles that climate, productivity, environmental heterogeneity and the presence of biomes and rivers may play in the structuring of species assemblages. For each 110 km x 110 km-cell on a grid map of America, we determined the number of species (SR) and estimated the mean Gower index (MDiv) based on 12 morphological attributes. We performed bootstrapping analyses of species assemblages to identify whether those assemblages were more similar or dissimilar in their morphology than expected by chance. We applied a multi-model selection procedure and spatial explicit analyses to account for the association of diversity-environment relationships. MDiv and SR both showed a latitudinal gradient, although each peaked at different locations and were thus not strictly spatially congruent. SR decreased with temperature variability and MDiv increased with mean temperature, suggesting a predominant role for ambient energy in determining Triatominae diversity. Species that were more similar than expected by chance co-occurred near the limits of the Triatominae distribution in association with changes in environmental variables. Environmental filtering may underlie the structuring of species assemblages near their distributional limits.

Demographic fitness of Belminus ferroae (Hemiptera: Triatominae) on three different hosts under laboratory conditions

Triatominae are widely recognised for their role as vectors of Trypanosoma cruzi. One of the main biological characteristics of this subfamily is their obligate haematophagous condition. However, previous studies on Belminus herreri and Belminus ferroae suggested that cockroaches are their principal hosts in domiciles. Due to this peculiar behaviour, the aim of this study was to analyse several demographic and reproductive parameters of B. ferroae fed on three different hosts (mice, cockroaches and Rhodnius prolixus) and relate B. ferroae fitness to these alternative hosts. The cohorts were reared under constant conditions. The egg hatching rate was similar for cohorts fed on cockroaches (69.4%) and R. prolixus (63.8%), but was much lower for the cohort fed on mice (16%). The development time from the nymph to adult stage and the average age of first reproduction (α) presented lower values in the cohort fed on cockroaches, which is consistent with the higher population growth rate associated with this host. Demographic parameters [intrinsic rate of natural increase, finite rate of population growth, net reproductive rate and damping ratio] showed statistically significant differences between the cohorts. Analysis of the life history of B. ferroae revealed a higher fitness related to the cockroach. The implications of these results for the origin of the subfamily are discussed.

Ecological patterns of blood-feeding by kissing-bugs (Hemiptera: Reduviidae: Triatominae)

Host use by vectors is important in understanding the transmission of zoonotic diseases, which can affect humans, wildlife and domestic animals. Here, a synthesis of host exploitation patterns by kissing-bugs, vectors of Chagas disease, is presented. For this synthesis, an extensive literature review restricted to feeding sources analysed by precipitin tests was conducted. Modern tools from community ecology and multivariate statistics were used to determine patterns of segregation in host use. Rather than innate preferences for host species, host use by kissing-bugs is influenced by the habitats they colonise. One of the major limitations of studies on kissing-bug foraging has been the exclusive focus on the dominant vector species. We propose that expanding foraging studies to consider the community of vectors will substantially increase the understanding of Chagas disease transmission ecology. Our results indicate that host accessibility is a major factor that shapes the blood-foraging patterns of kissing-bugs. Therefore, from an applied perspective, measures that are directed at disrupting the contact between humans and kissing-bugs, such as housing improvement, are among the most desirable strategies for Chagas disease control.

Re-infestation of houses by Triatoma dimidiata after intra-domicile insecticide application in the Yucatán peninsula, Mexico

In most countries, Chagas disease transmission control remains based on domestic insecticide application. We thus evaluated the efficacy of intra-domicile cyfluthrin spraying for the control of Triatoma dimidiata, the only Chagas disease vector in the Yucatán peninsula, Mexico, and monitored potential re-infestation every 15 days for up to 9 months. We found that there was a re-infestation of houses by adult bugs starting 4 months after insecticide application, possibly from sylvatic/peridomicile areas. This points out the need to take into account the potential dispersal of sylvatic/peridomestic adult bugs into the domiciles as well as continuity action for an effective vector control.

Factores biológicos y ecologicos en la enfermedad de Chagas, 2

Se incluyen distintos trabajos relativos a epidemiología, biología y ecología de vectores, paasitología, control y situación regional de la enfermedad de Chagas en los distintos países de las Américas, analizándose también la influencia de los factores biológicos, ecológicos y socieconómicos en los aspectos tratados

Epidemiología - vectores / Epidemiology - vectors

Se presentan varios trabajos referidos a diferentes aspectos epidemiológicos, ecológicos y biológicos de la enfermedad de Chagas: sinopsis epidemiológica de la enfermedad de Chagas, su problemática geográfica y técnicas de estudio -incluyendo el estudio en ambiente silvestre-; métodos de crianza y alimentación de triatominos; fisiología, desarrollo y comportamiento de estos insectos y su ecología. Se reviere con mayor detalle a Rhodnius prolixus, Panstrongylus megistus, Triatoma dimidiata y Triatoma infestans

Parásitos - reservorios - control - situación regional / Parasites - reservoirs - control - regional situation

Reúne diversos trabajos sobre parásitos, reservorios, control y situación regional de la enfermedad de Chagas, refiriéndose aspectos de la biología del Trypanosoma cruzi y Trypanosoma rangeli y la relación hués ped-parásito respectiva; de los factores socieconómicos relativos al vector de la enfermedad de Chagas, políticas sanitarias y de control químico e integrado (actualizándose sobre insecticidas disponibles); y, finalmente, se mencionan los reservorios de Trypanososma cruzi conocidos y la situación regional en cada uno de los países de las Américas - informándose sobre epidemiología; especies de triatominos identificadas, su ecología, distribución geográfica dentro de cada país y ciclo biológico; y reservorios que fueron identificados; y en algunos casos, se describen los programas de control realizados y las dificultades que en éstos existieran

Ecología poblacional de los triatominos / Population ecology of triatominae

Se revisan , aunque no eshaustivamente, los conocimientos existentes sobre ecología y dinámica poblacional de triatominos: influencia, en la regulación de sus poblaciones, de; les factores físicos ambientales (clima, temperatura, hábitat), de la alimentación, (en tanto regulador del tamaño de las poblaciones -densodependencia-), del comportamiento (en la búsqueda y orientación de hospedadores, disposición y ubicación de los diferentes individuos de una población: alta densidad local y factores de atracción), de los mecanismos de dispersión activa, y la efectividad de los enemigos naturales potenciales (posible control biológico); así como se analizan los cambios numéricos de las poblaciones de triatominos: abundancia poblacional, estructura de edades, tablas de vida y mortalidad y efectos relacionados a la densidad