Can brain structure help to resolve interordinal relationships in insects?

While the monophyly of most insect orders is well supported by morphological data, relationships among orders are still largely undecided. Postulated interordinal relationships are often based on relatively few morphological characters or characters of questionable phylogenetic signifi cance. In studies based on molecular evidence interordinal relationships are usually not signifi cantly supported. Depending on the molecule under scrutiny or on the method of data analysis molecular studies often produced confl icting hypotheses on insect phylogeny. One organ that provides a large amount of independent morphological characters and that has as yet been scarcely utilized by insect phylogenists is the supraoesophageal ganglion or brain. Drawing from the vast literature on insect neuroanatomy, this review explores the value of neuronal characters for deriving relationships among insect orders.