Biological assessment ofEncarsia citrina(Hymenoptera: Aphelinidae) a parasitoid of euonymus scaleUnaspis euonymi(Hemiptera: Diaspididae)
Laboratory studies were conducted to assess 1) the ovipositional preference of Encarsia citrina for host’s age by exposing it to 5–20-day-old scales 2) the effect of temperature (17.5, 20, 25, and 28 °C) and parasitoid density (1, 2, 3, 4, and 5 females/30 2nd instar) on host foraging 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 the increase in parasitoid density at 20 °C reduced the progeny production in E. citrina, due to the increase of mutual interference, it was able to distribute its progenies among the hosts more regularly. The highest values of killing power (k-value) were also obtained at 20 °C and the ratio of 4 parasitoid females/30 hosts. The shortest and longest handling time (Th) was measured at 20 and 17.5 °C, respectively. Accordingly, 20 °C is suitable condition to Encarsia reproductive and activity. E. citrina seems to be a promise candidate to control U. euonymi from late spring to early summer as well as during autumn, where the temperature is frequently around 20 °C. Therefore, parasitoid releases within this period on the early 2nd 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.