Authors studied the feeding preference of 1St instar nymphs of Triatoma infestans (Klug,1834) and T. melanosoma Martinez, Olmedo & Carcavallo, 1987 under laboratory conditions, using the precipitin test. The technique was to offer four different feeding sources simultanously: dog, cat, rat and pigeon. A total of 629 nymphs were observed, 381 of wich accepted to feed. From the last total number, 183 were T. infestans and 198 T. melanosoma. Results show that T. infestans fed mainly in dogs (27%), followed by rodent (21%), pigeon (15%), cat (13%), and associations of dog and cat (2%), pigeon and dog (1%) and cat and rodent (1%). T. melanosoma have fed mainly in dos, as T. infestans did (29%), followed by cat (25%), pigeon (10%), rat (8%) and associations of dog and cat (3%), cat and rat (1%) and dog and rat (1%).
Keyword: Triatoma infestans, T. melanosoma, feeding choice.