Abstract The scutellerid shield bug, Deroplax silphoides (Thun.) (Hemiptera: Scutelleridae), is a new recorded insect species (in Egypt) attacking the ornamental plant, Dodonaea viscosa (L.). The bug feeds by sucking sap from flowers and green seeds of this plant and sometimes from the very tender young apical leaves. Abundance of both the bug and its associated egg parasitoid Trissolcus basalis Woll. (Hymenoptera: Scelionidae) showed two generations of the bug peaking at the end of March and end of April. Thereafter, the non-parasitized individuals entered a summer aestivation till spring of next year synchronizing with the flowering time of its host plant D. viscosa. The scelionid egg parasitoid, T. basalis, showed also two generation on eggs of the bug in March and April. The parasitism rate reached 68.4 and 70.5% in 2016 and 2017, respectively. The life time fecundity of mated females reached an average of 49.5 ± 2.1 eggs. Adult life span for male and female parasitoid was 19.3 ± 1.0 and 23.5 ± 1.2 days, respectively. Some other biological aspects of the bug and its parasitoid were studied.