【Background】 Bemisia tabaci "Q" has become one of the most important invasive pests in China due to their rapid expansion and the huge economical losses. The extensive use of chemical insecticides has resulted in the development of high resistance against several insecticides. Therefore, biological control is a promising alternative for developing longterm integrated management of this invasive pest. 【Method】 In this study, the capacity of host feeding and parasitism by Eretmocerus hayati Zolnerowich and Rose on various nymphal stages of B.tabaci "Q" was determined under laboratory conditions. 【Result】 E.hayati could parasitize and hostfeed on various whitefly stages. A female parasitoid killed 10.[KG-*8]7 first, 6.[KG-*8]4 second, 6.[KG-*8]7 third and 5.[KG-*8]0 fourthnymphs/48 h by host feeding. E.hayati exhibited a tendency to feed on more hosts with increasing of host stage. There was a significant difference in the number of nymphs parasitized by E.hayati of different nymphal stage. Generally, female wasp parasitized more second and third instars (25.[KG-*8]4 and 27.[KG-*8]5 nymphs/48 h, respectively), followed by first (22.[KG-*8]1) and fourth instars (16.[KG-*8]5). 【Conclusion and significance】 These results indicated E.hayati exhibited the potential as biocontrol agent to control the invasive whitefly, B.tabaci "Q" through both host feeding and parasitism.