Medical and Veterinary Entomology zyxwvut (1989) zyxwvu 3, 179-194 Population dynamics of zyxwv Triatoma infestans under natural climatic conditions in the Argentine Chaco D. E. GORLA and C. J. SCHOFIELD* Ciencias Exactas, Fisicas y Naturales, Universidad de Cordoba, Argentina, and *Department of Entomology, London School of Hygiene and Tropical Medicine, U. K. Catedra de Entomologia, Facultad de ABSTRACT. Using experimental chicken houses at a site in central Argentina where the bug Triatoma infestans (Klug) is endemic, nine populations of this vector of Chagas disease were monitored during a 34- month period. Bug populations with four chickens as hosts were consis- tently larger than those with two chickens as hosts. Age structure of the bug population followed a similar pattern irrespective of the initial age structure. Egg to adult mortality was consistently around 98.5% and there was no consistent evidence for density-dependent mortality. There was some evidence for density dependence in fecundity and recruitment rates, but these were heavily constrained by low temperatures during the winter months. Nymphal development rates correlated most strongly with mean minimum temperatures rather than with mean maximum temperatures. We conclude that vector control using insecticides against this species would be most effective at the onset of winter, when recovery of any surviving populations would be inhibited by low temperatures. Key words. Triatoma infestans, population dynamics, density-depen- dence, Chagas disease, Argentina. zyxw Introduction Triatoma infestans (Klug) (Hemiptera: Reduviidae) is the most important and widespread vector of Trypanosoma cruzi Chagas, causative agent of Chagas disease. T. infestans is widely distributed in Argentina, Bolivia, Brazil, Chile, Paraguay, southern Peru and Uruguay, where it probably contributes to more than half of the estimated 24 million cases of this disease (Lgt zyxwvuts & Wygodzinsky, 1979; Correspondence: Dr C. zyxwvut J. Schofield, Department of Entomology, London School of Hygiene and Tropical Medicine,--Keppel Street, Gowe; Street, London WClE 7HT. Schofield et al., 1987). Except in the Cochabamba valley of Bolivia (Dujardin et zy al., 1987), T.infestans is confined to domestic and peridomestic habitats where it lives and breeds in the cracks and crevices of poor quality houses and outbuildings, emerging at night to suck blood from its vertebrate hosts. Knowledge about the population characteris- tics of T. infestans comes from laboratory studies (e.g. Rabinovich, 1972; Schofield, 1982) and field observations of domestic populations over relatively short periods (e.g. Schofield, 1980a, b). More detailed studies under natural condi- tions are inhibited by the cryptic behaviour of the bugs, operational problems of long-term 179