Biosystematics of the Muellerianella complex (Homoptera, Delphacidae): host‐plants, habitats and phenology

. 1. Ecological differences between closely related species and forms of the planthopper genus MueIlerianella (Delphacidae) were studied. 2. In the field M.brevipennis and M.faimairei are restricted to Deschampsia cespitosa and Holcus lanahis/H.mollis . respectively. M.extrusa is mainly found on Molinia caerulea , but has also been recorded from other grass‐species. Triploid all‐female forms which reproduce by gynogenesis usually live on Holcus together with M.fairmairei . Other gynogenetic populations were found on Bromus ramosus, Deschampsia flexuosa and Calamagrostis canescens . 3. Breeding experiments showed that the diploid species cannot be maintained on each other's host‐plants, but accept other grass‐species. 4. Due to overlapping habitat requirements of the host‐plants, ecological isolation between the Muellerianella species is incomplete. 5. M.extrusa lives in bogs, moors and forests on poor acid soil. M.brevipennis is found in forests, carr, fens and in extensively managed grasslands. M.faimairei and associated triploid forms occur mainly in grasslands and other man‐made habitats. The habitats of all three species are usually wet. 6. In most parts of Europe M.brevipennis and M.extrusa are monovoltine and M.fairmairei is mostly bi‐or polyvoltine.