Four-armed airflow olfactometer was used to determining the foraging behavior of Pteroptrix longgiclava (Girault) (Hymenoptera: Aphelinidae) and Encar siagigas (Tshumakova) (Hymenoptera: Aphelinidae) to the essential oils which em itted from the healthy bark of Populus pseudo-simonii ×P. Nigra, the infested b ark injured by Quadraspidiotus gigas (Thiem & Gerneck), the body and scale of fi xed 1st-instar-nymph of Q. Gigas. The results from these experiments showed that the volatile oils produced from the injured bark and from the scale of fixed 1s t-instar-nymph had a higher attractive ability to female adults of the two species of wasps. The essential oil produced from the scale of the pest at dosages of 3-7μL and the essential oil emitted by injured bark at dosages of 5-9 Μl had a stronger alluring effect on the host searching behavior of Pteroptrix longgiclava. The essential oil from the body of fixed 1st-instar-nymph of Q. Gigas also had certain effect on the host locating effort of Pteroptrix longgiclava and Encar siagigas. Those two wasps did not shown any reaction to the essential oil produced by the healthy bark of poplar.