Net-winged midges (Diptera: Blephariceridae): a food resource for brook trout in montane streams

摘要

We report on the importance of net-winged midges (Diptera: Blephariceridac) in the diet of three native populations of brook trout, Salvelinus fontinalis (Mitchill). One population, studied mostly during 1992 and 1993, was from the Rapidan River, Shenandoah National Park, Virginia. The other populations, studied in 1993 and 1994, were from Trail Creek and North Fork Rock Creek, both subalpine streams in Medicine Bow National Forest, Snowy Mountains, Wyoming. Rapidan River samples contained 411 larvae and adults, mostly of Blepharicera appalachiae Hogue & Georgian, recovered from 121 trout. During the study period, there were marked shifts in the relative consumption of larvae to adult Bl. appalachiae, then to Bl. similans Johannsen. These shifts presumably reflect temporal patterns of blepharicerid activity and perhaps changes in trout predatory behavior (benthic to surface feeding). At Wyoming streams, fourth-instar larvae and adults of the net-winged midge, Agathon elegantulus von Roder. were recovered from 34 trout. Relative to the Rapidan population, western trout populations consumed lower numbers of blepharicerids. Because net-winged midges arc moderately large flies that can be seasonally abundant in many streams, we posit that blepharicerids can be a significant component of trout diets.