Abstract: 【Aim】 This study aims to investigate the neuropil structures of the brain of the 5th instar larva of the tea geometrid, Ectropis obliqua Prout and to reconstruct their three-dimensional models. 【Methods】 The immunohistochemistry with synapsin antibody was used to characterize the anatomy of the neuropil structures of the brain. The laser scanning confocal microscope was used to acquire the confocal image stacks of the brain and the digital three-dimensional reconstructions were created by using the image analysis software AMIRA. 【Results】 The immunostaining with synapsin antibody revealed that there are many areas with dense synapse in the brain of the 5th instar larva of E. obliqua, which form different neuropil structures of brain. The larval brain of E. obliqua is composed of three main parts: protocerebrum, deutocerebrum and tritocerebrum. The protocerebrum contains several paired neuropils,including optic lobes, mushroom bodies, protocerebral bridges and lateral accessory lobes, and an unpaired neuropil of central body. The optic lobes are located posteriorly to the lateral parts of the protocerebrum. The mushroom body is located on the midline of each half brain. The central body is located in the center of brain. The protocerebral bridges are located dorso-posteriorly to the central body, while the lateral accessory lobes are located ventro-anteriorly to the central body. The protocerebrum is the largest part of the brain. In addition to these prominent neuropils, the protocerebrum at its lateral, ventral and dorsal parts also contains a midbrain which accounts for 66% of the brain neuropils. The boundaries of different parts of the midbrain, however, are too fuzzy to be discriminated. The deutocerebrum mainly consists of a pair of antennal lobes. The tritocerebrum at the entrance of circumoesophageal connectives into the brain is located in ventral part of the brain and under the antennal lobe. 【Conclusion】 The three-dimensional models of the brain including the neuropils were reconstructed. The volumes of the neuropils were calculated and their spatial relationships were determined. The results show that the brain of the 5th instar larva of E. obliqua is small and simple, corresponding to undeveloped visual and olfactory sensory organs as well as simple behavioral task at its larval stage.  

Key words: Ectropis obliqua, larva, brain, neuropil, three-dimensional model