Changes in prey preferences of dragonfly naiads of Rhionaeschna multicolour (Hagen, 1861) (Odonata: Aeshnidae) in the presence and the absence of macrophytes

We offered prey consisting of the rotifers, cladocerans, copepods, amphipods, dipterans and ephemeropterans to the pre-starved and sorted in three size groups of naiads of Rhionaeschna multicolour (Hagen, 1861) in the presence of the macrophyte Egeria densa Planchon and without it. The naiads consumed up to 25 prey items or in terms of biomass (wet weight) up to 7 mg within 2 h. Biomass intake increased with increasing predator's size. Prey consumption was significantly lower in presence of plants. The cladocerans Ceriodaphnia dubia Rihcard, 1894, Daphnia mendotae (Taylor and Hebert, 1993) and Ilyocryptus sp. were consistently preferred by the dragonfly naiads while Simocephalus vetulus (Müller, 1776), Alona guttata Sars, 1862 and Scapholeberis kingi Sars, 1888 were avoided with and without macrophytes. This study suggests that dragonfly naiads structure the zooplankton community by selective feeding.