Expression of heat shock protein 70 (Hsp70) is widely regarded and used as an indicator of cellular stress. However, recent data suggest that insect diapause may inhibit the increased expression of Hsp70 typical of the heat stress response. Here, we evaluated Hsp70 expression after heat stress in relation to diapause, in blueberry maggot, Rhagoletis mendax Curran (Diptera: Tephritidae), pupae. First, the respiration rates of laboratory-reared pupae were measured to estimate the limits of diapause. Then, toward the beginning and completion of diapause, pupae in prediapause, diapause, and postdiapause were exposed to similar periods of heat stress consisting of 1 h at 25 (control), 36, 40, and 44°C. Pupae were immediately frozen, and Hsp70 expression was determined by SDS-PAGE, Western blot, and immunodetection using a monoclonal antibody specific for heat-inducible Hsp70. Hsp70 was present at normal temperature (25°C) in diapausing pupae both toward the beginning and completion of diapause. Expression of Hsp70 always increased after heat stress irrespective of the diapause status of the pupae. These data support previous findings suggesting the presence of Hsp70 throughout diapause and indicate that even during diapause Hsp70 expression is responsive to heat stress. These results support the use of Hsp70 expression to study differential adaptation to heat stress during pupal diapause.