Virgin fruit fly females and males were stressed by placement into a confined space without food for 3 hours. Part of stressed flies were subjected to terahertz irradiation (0.1-2.2 THz) during 30 min. Life span of individual flies was evaluated. Terahertz radiation had some positive influence on male survival during the stage of monotonic decrease in flies number and negative effect during the stage of relatively stable number of flies. The survival of irradiated females on the stage of sharp decline in the number of flies was higher than in stressed and control females. Authors propose that terahertz radiation has an indirect effect on gene expression and signaling pathways which control the survival and life span of Drosophila.