Abstract: 【Aim】 This study aims to investigate the biological characteristics of the parasitoid Asobara japonica parasitizing Drosophila melanogaster and to determine the effects of its parasitization on the host growth and immune responses. 【Methods】The developmental duration and morphological characterastics of A. japonica at different developmental stages, the parasitism rate and emergence rate of A. japonica after parasitization on the 2nd instar larvae of D.melanogaster, the changes of host pupation time and transcriptional levels of 15 important genes of host in different immune pathways (SPE, Toll, Myd88, Dif and Drosomycin involved in Toll pathway, PGRP-LE, PGRP-LC, imd, Relish and Diptericin involved in Imd pathway and Spn27A, MP2, yellow-f2, DoxA2 and PPO1 involved in PO pathway) in the parasitized 2nd instar larvae of D. melanogaster were investigated and analyzed by anatomical imaging and qRT-PCR technology. 【Results】 The developmental duration of egg stage, larval stage and pupal stage of A. japonica under the conditions of 25±1℃, 50%±1% relative humidity and photoperiod of 16L∶8D was 2.38±0.01, 5.36±0.07 and 8.30±0.04 d, respectively. After parasitizing the 2nd instar larvae of D. melanogaster, the parasitism rate and wasp emergence rate of A. japonica were 94.9%±4.0% and 64.3%±7.1%, respectively. Moreover, after being parasitized by A. japonica, the pupation time of D. melanogaster with 50% pupation rate was prolonged by 0.5 d, and the transcriptional levels of the antibacterial peptide genes Drosomycin and Diptericin were up-regulated significantly, whereas that of the prophenoloxidase gene PPO1 was down-regulated as compared to the unparasitized control. 【Conclusion】 A. japonica can successfully and effectively parasitize D. melanogaster larvae through triggering host developmental delay and suppressing host melanization immune responses. The results provide some useful information for the massive release programs of the agriculturally important parasitoid species A. japonica. 

Key words: Asobara japonica, Drosophila melanogaster, parasitism, growth and development; immune response