External morphology and ultrastructure of the visual system of Arge similis (Vollenhoven, 1860) adults were investigated by light microscopy, scanning electron microscopy, and transmission electron microscopy. Each compound eye contains 2022 ± 89 (mean ± SE) facets in males and 2223 ± 52 facets in females. Arge similis has an apposition kind of compound eye composed of a cornea, a crystalline cone of four cone cells, and a centrally fused rhabdom made up of the rhabdomeres of eight large retinular cells. Each crystalline cone is surrounded by primary and secondary pigment cells with black spherical screening pigment granules measuring 0.60 ± 0.02 and 0.41 ± 0.01 μm in diameter, respectively. Based on our findings, the compound eye of A. similis can be expected to exhibit high adaptability to light intensity changes.

Eucryptorrhynchus scrobiculatus and E. brandti (Coleoptera: Curculionidae) are destructive weevils on Ailanthus altissima in China. This study examined phototactic behaviour of E. scrobiculatus and E. brandti in response to eight light-emitting diodes (LEDs) in the laboratory and field. Effects of gender, starvation, and light and dark experience on the phototactic behaviour of the insects were evaluated. The results demonstrated that, the two species of weevil were phototactic insects and most sensitive to violet light (400–405 nm), followed by blue–violet light (420–430 nm). They were less sensitive to red (655–660 nm), white (6000–6500 k), blue–green (470–480 nm), yellow (590–595 nm), blue (450–455 nm), and green (515–530 nm) light. In the light intensity range of 200–1000 lux, the light intensity had no significant effect on the phototatic behaviour of E. scrobiculatus and E. brandti. Phototactic behaviour of the insects was affected by gender. The phototaxis indices of the two species of weevil increased with starvation, reaching a plateau after 2 or 3 d of starvation. The phototaxis indices of E. scrobiculatus and E. brandti were significantly affected by various wavelengths of light following exposure to the light for 3 h or in different dark experience time. In the mark-release-recapture test, the number of E. scrobiculatus and E. brandti adults trapped by violet (400–405 nm) light traps is the largest. The information provided here provides a basis for survey and control of E. scrobiculatus and E. brandti.

Eucryptorrhynchus scrobiculatus and E. brandti are the main borers of Ailanthus altissima, causing serious economic and ecological losses. The external morphology and internal ultrastructure of the compound eyes of two related weevils were investigated with light microscopy, scanning electron microscopy, and transmission electron microscopy. E. scrobiculatus and E. brandti possess a pair of reniform apposition compound eyes and contain about 550 ommatidia per eye. The interommatidial angle of E. scrobiculatus and E. brandti are 7.08 ± 0.31° and 4.84 ± 0.49°, respectively. The corneal thickness, rhabdom length, and ommatidium length of E. scrobiculatus are significantly greater than those of E. brandti. Under light-adapted conditions, the pigment granules are mainly distributed at the junction of the cone and the rhabdom, and the diameter and the cross-sectional area of the middle end of the rhabdom is increased in the two weevil species. Under dark-adapted conditions, the pigment granules shift longitudinally and are evenly distributed on both sides of the cone and the rhabdom, and the diameter and cross-sectional area of the middle end of the rhabdom are decreased. The discrepancy in visual structure is beneficial for adaptation to niche differentiation of the two related species. The present results suggest that the two weevils possess different visual organ structures to perceive visual information in the external environment.