Pupae of the Mexican fruit fly, Anastrepha ludens (Loew) (=mexfly), were placed outdoors at two localities in northeastern Mexico in order to measure mortality rates during this phase of the life cycle. Replicates were placed monthly in citrus orchards and in a montane canyon where native host plants supported wild mexfly populations. Replicates were placed in sheltered sites under trees and in exposed sites between trees. Adult flies emerged from 38% of these pupae. Deermice, Peromyscus leucopus (Rafinesque) and P. boylii (Baird), were found to destroy 34% of the total pupae. There was no difference in predation rates or adult eclosion between the orange grove and the montane canyon. There were significant (P = 0.05) differences in predation rates among months and in pupal survival between sheltered and exposed sites, with greatest survival of pupae in the sheltered sites during the summer months. Only weak correlations were found between monthly mortality rates and temperature and moisture extremes. The effects of weather variables were probably masked by the pattern of predation. In the native habitat variable predation rates seemed to result from natural cycles in the abundance of mice or from temporal shifts in their food supply. In the citrus orchard cultural practices such as irrigation and weed control displaced or reduced the rodent populations resulting in lower predation rates during some months.