A phylogenetic interpretation of the Brachycera (Diptera) based on the larval mandible and associated mouthpart structures

Abstract. Based on outgroup comparison, the various components of the larval mandible of the Brachycera and their homologies are described. The final instar larval mandible of the Brachycera ground plan is comprised of a distal pointed hook and an inverted 'U'-shaped basal sclerite. The phylogenetic implications of the larval mandibular homologies and associated mouthpart structures for the current cladistic hypotheses of the Nematocera (Wood & Borkent, 1989) and orthorrhaphous Brachycera (Woodley, 1989) are evaluated.
A cladistic analysis of larval mouthpart characters largely supports the hypotheses of Wood & Borkent and Woodley. The presence of a pharyngeal filter is tentatively proposed as a synapomorphy of the Diptera exclusive of the Tipulomorpha and Bibionomorpha. Evidence is presented supporting a sister-group relationship between the Psychodomorpha ( sensu Wood & Borkent, 1989) and the Brachycera. The placement of the Pantophthalmidae in the Stratiomyomorpha is supported by the apomorphic development of the mandibular-maxillary complex and pharyngeal filter with posterior grinding mill. Additional larval mouthpart characters are proposed supporting the concept of the Eremoneura (Empidoidea + Cyclorrhapha). The ground plan of the Empidoidea appears to be characterized by the apomorphic development of a four-component mandible, in which the basal sclerite is subdivided into two connecting sclerites and a ventral sclerite. Morphological evidence is presented supporting the mandibular origin of the mouthhooks of the Cyclorrhapha.