Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae) is the most widely used parasitoid in biological control of Tephritidae programs around the world. Nevertheless, we have little information about the use of these parasitoids against Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae). This study was conducted to evaluate the thermal requirements for the development of D. longicaudata in 2 of its hosts, A. fraterculus and Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). Third instars of each fly species were exposed for 1 h to 50 couples of the parasitoid. Subsequently, the larvae were placed individually in glass jars maintained in chambers at temperatures of 15, 18, 21, 25, 28, and 31 °C, at 60 ± 10% RH and a photoperiod of 14:10 h L:D until the emergence of D. longicaudata. The rate of development of D. longicaudata, in both hosts, increased as temperature increased. The development period of egg-to-adult phases was used to estimate, by the hyperbola method, the lower development threshold (Dt) and the thermal constant (K) of D. longicaudata. Dt and K were, respectively, 7.83 °C and 322.58 degree days for individuals that developed in C. capitata, and 12.5 °C and 227.27 degree days for those that developed in A. fraterculus. Adult longevity was inversely proportional to temperature. The results indicated that D. longicaudata may not develop in Rio Grande do Sul in the winter, because it is very common that minimum temperatures in the months of Jun and Jul fall below the Dt. In the 4 fruit-producing regions of the state of Rio Grande do Sul, the average numbers of generations of D. longicaudata per year were estimated in A. fraterculus and C. capitata, respectively, as follows: Porto Alegre (11.16 and 13.12), Pelotas (7.97 and 10.89), Bento Goncalves (6.99 and 10.05), and Vacaria (4.84 and 8.28).