Encarsia citrina (Craw.) is considered as a promising parasitoid to be used as a bio-agent against the cosmopolitan diaspidid insect, Unaspis euonymi (Comstock). Laboratory studies were carried out to determine 1) the ovipositional preference of E. citrina for host's age by exposing it to 5-20 day- old scales 2) effect of  temperature (17.5, 20, 25, and 28°C) and  parasitoid's density (1, 2, 3, 4, and 5 females/30 hosts) on host searching efficiency of E. citrina.  E. citrina significantly preferred 10 day-old scales with the highest emergence rate. Temperature had significant effect on the searching efficiency of E. citrina over the range of 17.5–28°C. The highest rate of search was obtained at 20°C. Although increasing parasitoid density at 20°C reduced progeny production in E. citrina due to the increase of mutual interference, it was able to distribute its eggs among the hosts more regularly. The highest values of killing (k-value) were also obtained at 20°C and the ratio of 4 parasitoid females/30 hosts. The shortest and longest handling time (T_h) was measured at 20 and17.5°C, respectively. Accordingly, 20°C is suitable condition to Encarsia reproductive and activity.  E. citrina seems to be a good candidate to control U. euonymi from late spring to early summer as well as during autumn in regions like Austria, where the temperature is frequently around 20°C. Therefore, parasitoid releases within these easons on the early 2^nd instar (10 days old) with a ratio of 1 parasitoid: 7.5 hosts have to be considered in the future biocontrol program of U. euonymi.