Immature stages of the membracid Guayaquila projecta (Funkhouser) (Hemiptera: Cicadomorpha: Membracidae), collected in San Salvador de Jujuy, Argentina on Bougainvillea glabra Choisy (Caryophyllales: Nyctaginaceae), are described in detail based on specimens reared in the laboratory. Like other membracids, this species has five nymphal instars, not seven as previously reported. Morphological characters for identifying the different instars of G. projecta, determining the sex of later instars and distinguishing this species from other members of the Guayaquila pugnax group, are discussed. At 19 ± 4°C, RH 59 ± 9%, and a 12:12 L:D photoperiod, the time required for development from egg to adult emergence was 73 ± 5 days.