Abstract: Allometry is an important strategy for insects to adapt to the surrounding environment. Visual cues are the key information for host selection and flight movement of Empoasca onukii. With the growth and development of E. onukii, the size and mobility of the leafhopper gradually increase, and the morphology of the compound eye also changes significantly. In this study, histological and behavioral methods were used to determine the morphological structure and visual ability of the compound eye of E. onukii at different ages. The results show that the visual ability gradually increased during the growth and development process of E. onukii. From 1^st instar to 5^th instar, the optical sensitivity of the nymph increased from 0.04 μm²·sr to 0.11 μm²·sr, and the visual acuity increased from 0.086 cycles per degree (cpd) to 0.112 cpd. Both of optical sensitivity and visual acuity were consistent with the allometric growth, but their growth rates were slower than that of the size of nymphs. After the emergence of nymphs, the optical sensitivity of the center region of the compound eye decreased and there was a significant difference between the male and the female. Although the visual acuity kept increasing, the compound eye of E. onukii was still a low-resolution organ with limited effective visual distance. This study confirms that E. onukii slows down the growth rate of visual ability to prioritize the development of body size and motion-related organs, and focuses on the increase of visual field to facilitate to perceive visual cues in a wide range.

Key words: Empoasca onukii, allometry, growth and development, compound eye, optical sensitivity, visual acuity