Density regulation of domestic populations of Triatoma infestans in Brazil

Abstract

Twenty old houses in a rural area of central Brazil were sampled monthly for Triatoma infestans during 16 months. The samples indicated peak adult emergence between January and May, preceded by peak emergence of stage V, IV and III nymphs respectively. Stage I and II nymphs were rarely taken in the samples. A much smaller peak of adult emergence occurred in September; thus the two peaks of adult emergence during the year were consistent with the approximately six months duration of egg-to-adult development usually recorded in laboratory studies. During January, 1977, when the study began, all houses were searched for dead bugs, exuviae, eggs and eggshells. These samples were used to calculate stage mortalities, from which a simple life-table was constructed. These data were combined with laboratory data concerning stage development times and female longevity and fecundity. Sensitivity analysis of the life-table showed it to be most sensitive to small changes in daily mortality rate and total egg-to-adult development time. The data were used to advance an hypothesis that the size of domestic populations of T. infestans is mainly controlled by changes in the egg-to-adult development time and, to a lesser extent, by changes in female reproductivity. Both these factors are in turn controlled by the nutritional status of the bug population, which, if the supply of food, i.e. number of hosts, is constant, is dependent upon the density of the bug population. It is argued that this mechanism of density regulation functions within limits set by the prevailing ambient temperature.

Interacción entre poblaciones de Triatoma infestans y Triatoma sordida

“…En T. infestans se observo un pico de emergencia de adultos desde febrero a abril, precedido de valores máximos en la producción de ninfas de tercero y cuarto estadio en diciembre y de quinto en enero, en concordancia con lo verificado para la misma especie, en casas rurales de Mambaí, Brasil 18 .…”

“…Acerca de ello, Schofield 18,19 y Rabinovich 15 señalan que a mayores densidades corresponde un estado nutricional más bajo.…”

“…La primera, principal vector de Trypanosoma cruzi en la Argentina, es esencialmente doméstica, mientras que Triatoma sordida se encuentra preferentemente en el peridomicilio. No obstante, ambas especies fueron halladas juntas en la misma vivienda, o en estructuras peridomésticas, pero ocupando sitios diferentes 1,10,18 .…”

“…La primera, principal vector de Trypanosoma cruzi en la Argentina, es esencialmente doméstica, mientras que Triatoma sordida se encuentra preferentemente en el peridomicilio. No obstante, ambas especies fueron halladas juntas en la misma vivienda, o en estructuras peridomésticas, pero ocupando sitios diferentes 1,10,18 .Son numerosos los casos en que el hábitat doméstico ha sido colonizado nuevamente por la misma especie o por otras especies, las que desde sus biótopos invaden al domicilio. Así, por ejemplo, en Brasil se observó que a medida que las poblaciones de T. infestans disminuían en las viviendas, éstas eran reinfestadas por T. sordida y Panstrongylus megistus 16 .…”

Comparative developmental and susceptibility to insecticide of Bolivian and Brazilian populations of Triatoma infestans

“…In the present study the mean time taken to complete the developmental cycle was close to the six months average for both colonies, but differed significantly at 183.47±21.18 days for the Brazilian colony and 173.85±19.59 days for the Bolivian colony. As modelled by Schofield (1980) such differences can markedly influence the reproduction rate of the respective populations. Perlowagora-Szumlewicz (1975) stated that first instar nymphs of T. infestans, maintained at 24-28ºC, were able to feed on blood from the fourth day after hatching onwards.…”