Abstract: 【Aim】 Eutectona machaeralis mainly feeds on teak, a precious tree species. This study aims to observe and study the morphology, tissue structure and ultrastructure of the compound eyes of E. machaeralis adults, and to analyze the structural characteristics of the compound eyes, so as to lay a foundation for a better understanding of the relationship between the complex visual behavior and the photosensitive mechanism of this species. 【Methods】 Optical microscope, and scanning and transmission electron microscope techniques were used to observe the morphology, tissue structure and ultrastructure of compound eyes of E. machaeralis adults. 【Results】 The compound eyes of E. machaeralis adults are symmetrical compound eyes, born at the base of head antennae, and ellipsoidal in shape. The compound eyes of females and males have 2 300-2 755 and 1 950-2 316 ommatidia, respectively. The ommatidium is hexagonal, its surface is densely covered with corneal nipples, and there are occasional interfacetal hairs in the gap. Each ommatidium is composed of one cornea, four crystalline cone cells, one pair of primary pigment cells, six secondary pigment cells, 12 retinal cells distributed in different horizontal planes, and basement membrane. The centripetal cell membranes of 11 retinal cells along the longitudinal axis of the ommatidium are specialized into filamentous microvilli, forming radially arranged rhabdomere, which combine into a confluent rhabdom. The 12th retinal cell is located at the base of the ommatidium. Above the basement membrane, the ends of retinal cells and secondary pigment cells swell up, passing through the basement membrane in the form of axons. 【Conclusion】 The compound eyes of E. machaeralis are typical superposition eyes. There are no obvious differences in the arrangement and internal structure of ommatidia between the female and male adults, but the number and size of ommatidia in females and males present obvious sex dimorphism.

Key words: Eutectona machaeralis, ultrastructure, compound eye, ommatidia, superposition eye