X-ray diffraction pattern from the flight muscle of Toxorhynchites towadensis reveals the specific phylogenic position of mosquito among Diptera

Hiroyuki Iwamoto

The Diptera are a group of insects with only a single pair of wings (forewings), and are considered monophyletic (originating from a common ancestor). The flight muscle in Diptera has features not observed in other insects, such as the long Pro-Ala-rich peptide associated with tropomyosin, not with troponin-I as in other insects, and the formation of a superlattice by myosin filaments analogous to that in vertebrate skeletal muscle. Here we describe X-ray diffraction patterns from the flight muscle of a mosquito, Toxorhynchites towadensis (Culicidae), belonging to a primitive group of Diptera. The diffraction pattern indicates that myosin filaments in the flight muscle of this species do not form a superlattice. X-ray diffraction also shows meridional reflections that are not observed in other dipterans, but are present in the patterns from bumblebee (Hymenoptera) flight muscle. These observations suggest that the superlattice structure evolved after the common ancestor of Diptera had diverged from other insects. The flight muscle of mosquito may retain primitive structural features that are shared by Hymenoptera.