Species and processes in ecosystems are part of multi-trophic interaction networks. Plants represent the lowest trophic level in terrestrial ecosystems, and experiments have shown a stabilizing effect of plant diversity on higher trophic levels. Such evidence has been mainly collected in experimental grasslands. Forests are structurally more complex than grasslands and support the majority of the global biodiversity, but studies on multi-trophic interaction networks are missing in experimental tree diversity gradients. In a forest diversity experiment in southeast China, we examined how tree diversity affects the structure of trophobiotic networks. Trophobioses are tri-trophic interactions between plants, sap-sucking Hemiptera and honeydew-collecting ants that can be subdivided into a largely mutualistic Hemiptera-ant and an antagonistic plant-Hemiptera network. We inspected almost 7000 trees in 146 plots ranging from monocultures to 16 tree species mixtures and found 194 trophobioses consisting of 15 tree, 33 Hemiptera and 18 ant species. We found that tree diversity increased the proportion of trees harboring trophobioses. Consistent with the prediction that mutualistic and antagonistic networks respond differently to changing environments, we found that the generality index of the mutualistic Hemiptera-ant but not the antagonistic plant-Hemiptera network increased with tree diversity. High generality, maintained by high tree diversity, might correspond to higher functional stability. Hence, our results indicate that tree diversity could increase via bottom-up processes the robustness of ant-Hemiptera associations against changing environmental conditions. In turn, the plant-Hemiptera network was highly complementary, suggesting that host-specific Hemiptera species may be vulnerable to co-extinction if their host plants disappear. Based on our results, we provide possible future research directions to further disentangle the bottom-up effect of tree diversity on the structure of trophobiotic networks.