Ecological aspects of South American tripanosomiasis: II - local distribution and dispersion of triatomids in natural and artificial ecotopes

Abstract

A local distribution pattern of Triatoma sordida and Rhodnius neglectus is described after an intensive investigation on natural and artificial ecotopes. The work was carried in a region at north of the State of São Paulo, Brazil. Measures of dispersion pattern were made by the Morisita's indices showing contagious distributions to both bugs. The T. sordida population was clumped at houses and surrounding dwellings, while R. neglectus presented the same aspect but relater to palm trees. The first bug showed ubiquity patter including palms, dry trees and fences. These last two situations are not favourable for obtaining blood meals, who are much more easy obtained at human dwellings. By other side, the investigations at areas with more dense vegetation like bush, resulted in very few T. sordida and none R. neglectus, probably owing of other populations competition as predators reduvids bugs, found there with great density. So it seems logic remove that competition and triatomids remains free to increase in the residual ecotopes. From these, T. sordida is atracted to houses where the bugs may will found more available blood meals, and so the distribution pattern becomes contagious at these places characterizing the invasive aspect at these places. Beside this, the elimination of the early Triatoma infestans populations from dwellings by insecticide spraying (BHC), becomes vacant an ecological niche that seems, in this case, to be occupied by T. sordida. On the contrary, R. neglectus, specialized at palm trees, may found easily blood meals represented by birds and mammals nests and so, the contagious distribution is restricted at these ecotopes with little or even no tendence to invade houses. The persistence of Trypanosoma cruzi in the area was detected both by triatomids naturally infected found in dwellings and by positive xenodiagnosis obtained in Rattus norvegicus captured there. So, the possibility of increase of local transmission rate is emphasized.