Abstract: 【Aim】 Leptocybe invasa is an important pest of eucalyptus trees. This study ims to investigate the embryonic and postembryonic development of L. invasa so as to understand its biological characteristics and occurrence and infestation rules. 【Methods】 The female reproductive system, eggs and galls of L. invasa were dissected, its embryonic and postembryonic development were observed, and the volumes of the galls, chambers and larvae as well as the thickness of the parenchyma cell layer were measured at each developmental stage. 【Results】 The embryonic development of L. invasa is completed in 138 h, including three stages: the period of nutrition accumulation after egg laying (0-24 h), the embryonic stage (36-84 h), and the hatching stage (96-138 h). The developmental process of L. invasa in galls is consistent with that of the galls. The gall structure is composed of three basic layers including epidermal layer, mesenchymal layer and parenchyma cell layer from the outer side to the inner side. The increase rate of the larval volume of L. invasa showed a unimodal change trend with the time of development, and reached the maximum at 30 d. The increase rate of the gall showed a parabola-shaped change trend and the thickness of the parenchyma cell layer of the galls also showed a parabola-shaped change trend (increased rapidly in the early stage and decreased slowly in the later stage) with the time of development. 【Conclusion】 At the age of 25 d, L. invasa larva is still at the early instar with low food intake, but the thickness of the parenchyma cell layer (food) in the gall reached the maximum, which is prepared for the rapid growth of larva.

Key words: Leptocybe invasa, embryonic development, postembryonic development, gall; parenchyma cells