Adults of predaceous midges, such as Aphidoletes and Feltiella spp. (Cecidomyiidae), can be distinguished from those of plant-feeding fungus gnats, Bradysia spp. (Sciaridae), by wing venation. Bradysia spp. have a distinct, forked (Y-shaped) vein near the apex (tip) of each wing. Predaceous midges have a faint, forked vein in the posterior (outer) portion of wings.
Photo by Gorham JR. 1991. Insect and Mite Pests in Food: An Illustrated Key. Vol. 1. USDA Agric. Handb. 655. 1991 V1.pdf, fungus gnat. Midge adapted from Pritchard AE. 1953. The Gall Midges of California Diptera: Itonididae (Cecidomyiidae). Bull. Calif. Insect Survey 2(2):125-150.