Substrate complexity influences the preference of a predatory stonefly, Eusthenia costalis BANKS (Plecoptera: Eustheniidae), for its prey

Prey selection of the stonefly Eusthenia costalis was investigated by presenting late instars with a choice of three different prey species [Nousia sp. Navás (Ephemeroptera: Leptophlebiidae), Neboissoperla sp. McLellan (Plecoptera: Gripopterygidae) and Antipodeus sp. Williams and Barnard (Amphipoda: Paramelitidae)] or two distinct size classes of Nousia. To determine whether substrate complexity influences the foraging preference of E. costalis selection trials were conducted using two different levels of substrate complexity: "fine" (sieve dimension 1-4 mm), and "coarse" (8-16 mm); Stonefly nymphs selected Nousia in fine substrate and Neboissoperla in coarse substrate. Stonefly nymphs were not selective, based upon the size of Nousia prey in fine substrate, however, they preferred large Nousia in the more complex substrate. Irrespective of substrate complexity, as the size of E. costalis nymphs increased preference for Neboissoperla declined.