Peridomestic distribution of Triatoma garciabesi and Triatoma guasayana innorth-west Argentina

The Reduviid bugs Triatoma garciabesi Carcavallo et al. (Hemiptera: Reduvii dae: Triatominae), previously known as T. sordida Stahl in the semi-arid ch aco region, and T. guasayana Wygodzinsky & Abalos, vectors of Trypanosoma c ruzi Chagas (Kinetoplastida: Trypanosomatidae), were found to occupy wide b ut different ranges of ecotopes in the peridomestic environment. At Amama a nd nearby rural villages in north-western Argentina, a combined total of 12 33 specimens were collected from 325/2314 (14%) sites surveyed at 6-monthly intervals from November 1994 to November 1996. Triatoma garciabesi and T. guasayana displayed a significantly different distribution among peridomest ic ecotopes. Triatoma garciabesi predominated over T. guasayana in the prev alence of infested sites, the number of colonies and the number of bugs col lected. For T. garciabesi, the predominant ecotopes most likely to yield T. garciabesi repeatedly were the rugged bark of Prosopis alba or P. nigra (F abaceae) trees, where chickens roosted, and chicken coops. For T. guasayana the main ecotopes were goat or sheep corrals, piled materials and orchard fences. Triatoma garciabesi and T. guasayana were collected concurrently fr om the same site on 9/2314 (0.4%) occasions, and on different dates at the same site on 12 (0.5%) occasions. The observed low frequency of mixed popul ations (< 1%) was not significantly different from that expected from a hyp othesis of independence. Triatoma garciabesi clearly outnumbered T. guasaya na in four of the nine mixed populations, none of which persisted as such. Neither T. garciabesi nor T. guasayana colonized human habitations, even in the absence of T. infestans (formerly the predominant domestic vector of T . cruzi in this area), a situation that apparently has not changed in the l ast 50 years in northern Argentina.