External morphology of four species of Microdon immatures (Diptera: Syrphidae) from the Pacific Northwest

Biological studies of myrmecophilous Microdon often require identification of species solely from puparial or larval specimens. This study demonstrates use of the marginal band and dorsal reticulation characteristics in identification of immatures of four species of Pacific Northwest Microdon: M. albicomatus Novak, M. cothurnatus Bigot, M. piperi Knab, and M. xanthopilis Townsend. For these species, descriptions are given of prothoracic horns of pupae; marginal bands, dorsal reticulation processes, and spiracular tubercles of puparia and larvae; and chorions of eggs. In addition the cephalic segment and mouth parts are described for M. albicomatus . Keys to puparia, third instars, and second instars are provided.