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Passive dispersion

This mode of dispersion is the most important one to explain the territorial expansion of the main vectors.8 Triatominae migrate with their hosts, especially the Triatominae highly adapted to their host. Dujardin51 hypothesized that the main domestic populations of Triatominae (T. infestans, R. prolixus, T. dimidiata, T. rubrofasciata, etc.) realized a passive migration with humans because of their high adaptation to the human habitat and the hosts living there or around. T. infestans occupies seven countries in South America, T. dimidiata is found, like R. prolixus, in Central and South America, and T. rubrofasciata is a pantropicopolitan species. The large territories of these species may present discontinuities (R. pro- lixus is absent from Panama and Nicaragua, for instance) suggesting passive transportation by man, and appear as recent conquests, as suggested by their genetic structure and by historical records when available. The hypothesis is that they have been transported by their hosts (human hosts, but domestic rodents for T. rubrofas- ciata) far outside their natural ecotope, losing their contact with original silvatic foci, and increasing their dependency on human hosts.

The restricted habitat, the high dependency to humans and domestic animals, the loss of genetic resources from wild original populations, the genetic material reduction as observed by cytogenetic techniques,52 all these factors produced a vulnerable insect, with a likely homogeneous response to control measures throughout its territory.51 Some Triatominae increase their possibility to follow the host by producing gluing eggs. For arboreal species which may feed on birds, one can imagine the important and fast migrations possible for a small population of eggs, leading to founder effects if peripheral colonization is successful. This mechanism has been suggested to explain the colonization of Central America by R. prolixus,53 but was challenged by the historical revision made by Zeledon54 who suggested that Central America was colonized by human activities. The latter thesis was supported by genetic studies.55

Chickens and dogs have been suspected of being passive carriers of T. infestans when they enter houses and sleep in the bedrooms. However, no nymphs or adults of this or other triatomine were found in the skin of these domestic animals, in positive houses of the Argentinean arid chaco.36,56

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