Leaf-consuming insects play a crucial role in the green food chain. However, the island biogeographic patterns of leaf insect herbivory and the drivers remain unclear, thus restricting the understanding of biological cascade effects in island ecosystems. In this study, we selected 27 typical plots across 24 distinct islands in Zhoushan archipelago. We examined mining, sucking and chewing herbivory intensity on leaves of woody plants in theses plots. Linear regression and structural equation modeling were employed to dissect the biogeographical patterns of leaf insect herbivory, elucidating how island area and isolation directly or indirectly affect herbivory via plant species richness. The linear regression model showed that sucking herbivory increased with increasing island area (R2 = 0.22, P<0.01) and showed a significant decreasing trend with heightened isolation (R2 = 0.13, P<0.05). The structural equation model showed that, (1) island area and isolation had indirect effects on total herbivory (β = 0.24; β = –0.27), (2)island area had a direct effect (β = 0.29) on sucking, as well as indirect effects (β = 0.24), island isolation had an indirect effects on sucking (β = –0.27), (3)island area and isolation had no direct or indirect effects on mining and chewing. In conclusion, leaf insect herbivory exhibits distinct biogeographic patterns primarily determined by sucking with plant species richness serving as the underlying intrinsic driver. This study contributes to a deeper understanding of the relationships between plants and animals in island systems and their cascading effects.