J. R.  Vockeroth and Thompson, F. C., ?Chapter 52. Syrphidae?, in Manual of Nearctic Diptera, vol. 2, J. F.  McAlpine, Peterson, B. V., Shewell, G. E., Teskey, H. J., Vockeroth, J. R., and Wood, D. M., Eds. Ottawa: Research Branch, Agriculture Canada, 1987, pp. 713-743.