Abstract: Trophobiotic interactions between ants and honeydew-providing hemi pterans are widespread and are one of the key mechanisms that maintain ant super-abundance in ecosystems. Many of them occur inside ant nests. However, these cryptic associations are poorly understood, particularly those with hoppers (suborder Auchenorrhyncha). Here, we study tree-dwelling ant and Hemi ptera communities in nests along the Mt. Wilhelm elevational gradient in Papua New Guinea and report a new case of this symbiosis between Pseudolasius emery, 1887 ants and planthoppers. Fur thermore, we provide a worldwide review of other ant-hopper interactions inside ant-built structures and compare their nature (obligate versus facultative) and distribution within the suborder Auchenorrhyncha. The novel interac tions were observed in nests located at the tree trunk bases or along the whole trunks. Only immature planthopper stages were found inside nests, so full species identifications were not possible. However, nymph morphology and molecular data (18S and Coi genes) indicated four related species of the family Flatidae (infraorder Fulgoromorpha) associated with Pseudolasius. Ant-planthopper occurrences were relatively rare (6% of all trophobiotic interactions) and peaked at mid-elevation (900 m above sea level). Pseudolasius was the only genus associated with planthoppers in the communities, with most cases monopolised by a single species, P. breviceps emery, 1887. In contrast, all other ant genera tended various scale insects (Sternorrhyncha: Coccoidea). This apparent partner-specificity is rare: World wide, there are only about ten reported cases of obligate symbiosis in ant nests, distributed in five of the thirty-three Auchenorrhyncha families. Those trophobioses are randomly dispersed across the Auchenorrhyncha phylogeny, and thus likely originated multiple times independently. Further research on both adult and nymph hopper life history is needed to answer how these symbioses, notably rare in hoppers compared with other hemi pterans, are maintained.

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