Triatoma infestans, to be or not to be autogenic?

Autogeny, the ability to develop eggs without a meal in the adult stage, has been described in several groups of arthropods, especially hematophagous Diptera Nematocera. In obligate hematophagous hemimetabolous insects that feed on blood in all their instars, such as Triatominae, this concept gives rise to species with apparently facultative autogeny, such as Triatoma infestans. Generalized linear models were applied to explain egg production by the predictor variables molting weight as a proxy of nymphal accumulated reserves and digested blood weight as an indicator of adult reserve in fasted, incompletely fed and engorged at repletion females. The relationship between these indicators of nutritional status and egg development turned out to be a continuous function in which, with molting weights greater than 254 mg, the insects are autogenic, but for the first batch of eggs with molting weights between 132 and 253 mg, they require one adult meal of at least 202 mg, and with molting weights less than 131 mg at least two meals are required. Both molting weight and blood intake could determine oocyte production in an additive manner, thus the concept of autogeny as a switch on-off phenomenon is not directly applicable to Triatominae. Nevertheless, autogenic ability would allow Triatominae with relatively long cycles to accelerate population growth under favorable or low competition conditions during colonization or recovery after a control intervention.

Ecology of fleas and their hosts in the trifinio of north-east Argentina: first detection of Rickettsia asembonensis in Ctenocephalides felis felis in Argentina.

Fleas are important in public health due to their role as parasites and vectors of pathogens, including Rickettsia. The aim of this study was to evaluate the diversity, abundance and prevalence of fleas and the presence of Rickettsia in the trifinio of north-east Argentina. Fleas from household and synanthropic animals were obtained from urban and periurban areas. They were taxonomically identified and samples of 227 fleas in 86 pools were analysed by polymerase chain reaction targeting the gltA and ompB genes of Rickettsia spp. The study revealed that Ctenocephalides felis felis was dominant on dogs, cats and opossums, with higher prevalence in the periurban area. The Shannon-Wiener and Morisita-Horn indices expressed differences in the diversity and similarity values of the absolute abundances of the species between the areas compared. DNA amplifications revealed 30.8% C. f. felis pools positive for Rickettsia spp. Phylogenetic analysis showed that the haplotype obtained was identical to Rickettsia asembonensis from Peru and Brazil. This is the first detection in Argentina of R. asembonensis that infects C. f. felis, and we emphasize the importance of conducting research from a 'One Health' perspective on the role of opossums and rodents in the integration of the transmission cycles of rickettsial bacteria.

Spatiotemporal dynamics of Lutzomyia longipalpis and macro-habitat characterization using satellite images in a leishmaniasis-endemic city in Argentina.

The spatiotemporal population dynamics of Lutzomyia longipalpis (Lutz & Neiva, 1912) (Diptera: Psychodidae) were evaluated in a city in Argentina in which visceral leishmaniasis is endemic. Over 14 sampling sessions, 5244 specimens of five species of Phlebotominae (Diptera: Psychodidae) were captured, of which 2458 (46.87%) specimens were L. longipalpis. Generalized linear models were constructed to evaluate the associations between L. longipalpis abundance and explanatory variables derived from satellite images. The spatial variable 'stratum' and the temporal variable 'season' were also included in the models. Three variables were found to have significant associations: the normalized difference vegetation index; land surface temperature, and low urban coverage. The last two of these were associated with L. longipalpis abundance only during summer and winter, respectively. This variation between seasons supports the development of models that include temporal variables because models of distributions of the abundance of a species may show different critical variables according to the climatic period of the year. Abundance decreased gradually towards the downtown area, which suggests that L. longipalpis responds to a meta-population structure, in which rural-periurban source populations that persist over time may colonize adjacent areas. This information allows for a spatiotemporal stratification of risk, which provides public health authorities with a valuable tool to help optimize prevention measures against visceral leishmaniasis.

Ecological characterization of a tick community across a landscape gradient exhibiting differential anthropogenic disturbance in the Atlantic Forest ecoregion in Argentina.

An ecological analysis of a tick (Ixodida: Ixodidae) community across a landscape gradient presenting differential anthropogenic disturbance in the Atlantic Forest ecoregion in Argentina was performed. Ticks were collected from vegetation and hosts between September 2014 and August 2016. A total of 12 697 free-living ticks and 3347 specimens from hosts were collected, including 317 ticks infesting humans. The values obtained show considerable species diversity in the forest environment accompanied by low equitability. The similarity index derived from a comparison of forest and agricultural environments was higher than that calculated by comparing forest and urban environments. The data suggest that although a cycle of one generation per year is apparent in some species, more than one cohort may co-exist within the populations of some of these species. Well-marked patterns of the seasonal distribution of free-living tick species emerged in environments with no anthropic modification. The results indicate that forest environments are more suitable habitats than agricultural and urban environments for many species of native tick, but are unsuitable for exotic species that have successfully established in environments that have been modified by man.

Intra-phylum and inter-phyla associations among gastrointestinal parasites in two wild mammal species.

A growing body of literature reveals that the interactions among the parasite community may be strong and significant for parasite dynamics. There may be inter-specific antagonistic interactions as a result of competition and cross-effective immune response, or synergistic interactions where infection by one parasite is facilitated by another one, either by an impoverishment of the host's defenses, parasite-induced selective immunosuppression, or trade-offs within the immune system. The nature of these interactions may depend on how related are the parasite species involved. Here we explored the presence of associations among gastrointestinal parasites (coccidia and helminths) in natural populations of two wild mammal species, the capybara (Hydrochoerus hydrochaeris) and the guanaco (Lama guanicoe). The associations explored were between the oocyst outputs of a selected Eimeria species and the other coccidia of that parasite community, and between Eimeria spp. and the predominant nematodes. The statistical analysis included adjustment for potential confounders or effect modifiers. In guanacos, the prevailing interactions were synergistic among the coccidia and between coccidia and nematodes (Nematodirus spp.). However, in capybaras, the interaction between nematodes (Viannaiidae) and Eimeria spp. depended on environmental and host factors. The relationship was positive in some circumstances (depending on season, year, sex, or animal size), but it appeared to become antagonistic under different scenarios. These antagonist interactions did not follow a particular seasonal pattern (they occurred in autumn, spring, and summer), but they were predominantly found in females (when they depended on sex) or in 2010 and 2011 (when they depended on the sampling year). These results suggest that the relationship between coccidia and nematodes in capybaras may be context dependent. We propose that the context-dependent immune investment documented in capybaras may be the cause of these varying interactions.