A global review and network analysis of phytophagous insect interactions with ferns and lycophytes

Ferns and lycophytes are the second and third largest lineages of vascular plants, yet our understanding of their interactions with phytophagous insects is very limited. In this study, we reviewed herbivorous insects, their feeding habits and host preferences on these two plant groups, searched for any evidence of coevolution, and discussed possible biases of our current knowledge on fern–insect interactions. We analyzed 2318 records of fern–insect interactions from 122 literature sources, based on the feeding habit of insects, fern taxa, and geographic location. We report interactions comprising 809 insect species (mainly Hemiptera, Lepidoptera, and Coleoptera) and 382 fern species (mainly Dennstaedtiaceae, Dryopteridaceae, and Pteridaceae). Leaf-chewers comprised over 50% of the species, followed by sap-sucking insects (29.1%) and spore feeders (6.5%). The overall interaction analyses revealed that the entire network was not significantly nested and had relatively low levels of specialization (H′ = 0.24). The interaction networks of Coleoptera were the most specialized at family (H′ = 0.40) and genus level (H′ = 0.65), whereas six out of 10 most specialized insect families were Lepidoptera (d′ ≥ 0.44). At the genus level, all networks had a plant-biased asymmetry. Although insect specialists were common, few cases of coevolutionary radiation have been documented. We discuss the possible biases of our dataset, which also highlight gaps to fill in future research and suggest that many more fern-feeding insects remain to be discovered, especially sap-sucking, gall-forming, and spore-feeding insects on modern fern groups.