|Kehl, S; Dettner, K: Predation by pioneer water beetles (Coleoptera: Dytiscidae) from sandpit ponds based on cropcontent analysis and laboratory experiments, Archiv für Hydrobiologie, 158, 109-126 (2003)|
Crop-content analyses of 898 pioneer beetles, belonging to five dytiscid species of sandpit ponds, (Coleoptera: Dytiscidae) were performed to identify possible nutritionally-based niches and competitive effects. Agabus nebulosus, Nebrioporus canaliculatus, Scarodytes halensis, Hygrotus confluens and Hydroglyphus geminus mainly feed on chironomid larvae and planktonic crustacea, especially Copepoda. However, a large amount of filamentous algae was found in the crops of A. nebulosus and H. confluens fed on Rotatoria, especially Keratella, while the small hydroporine H. geminus fed on the small nauplius larvae of Copepoda. Experiments were used to test the relative feeding preference of S. halensis for Copepoda and Cladocera and for dead or living plankton. Dead plankton was preferred, whereas the size of the plankton was important in the selection of Copepoda or Cladocera. The crop clearance times for different food items were also ascertained: no differences in digestion times of chironomid larvae, Chaoborus larvae and plankton were found.