P3.167  Monday, Jan. 6 15:30  More than just slippery – The impact of biofilm on the attachment of running water insect larvae DITSCHE-KURU, P.*; KOVALEV, A.; MICHELS, J.; KOOP, J.H.; GORB, S.N.; University of Washington, USA; University of Kiel, Germany; University of Kiel, Germany; University of Kiel, Germany; Federal Inst. Hydrology, Koblenz, Germany; University of Kiel, Germany pditsche@uw.edu

While terrestrial insects usually attach directly to the substrate, for aquatic insects the situation is more complex due to the presence of biofilms on primary substrates. In comparison with the primary substrates, these biofilms are usually softer and feature different surface structures and chemistries. Recent investigations indicate that the biofilm can strongly influence the ability of some mayfly larvae to attach to the substrate. The aim of this study was to test this assumption and prove the impact of biofilm on the attachment of mayfly larvae.
We (1) performed attachment experiments in a flow channel, (2) measured attachment forces generated by the claws of dissected legs and (3) characterised mechanical properties of the biofilm. The experiments were performed on substrates of different surface roughness each with and without biofilm.
Interestingly, on substrates with smooth or slightly rough surfaces, where the claws hardly find surface irregularities to grasp on, the presence of biofilm increased the attachment force of claws significantly. The larvae were able to endure higher flow velocities on these biofilm-covered smooth substrates in comparison to the biofilm-free smooth substrates. In contrast, on rough substrates the attachment force of claws decreased in the presence of biofilm. Nevertheless, on these rough substrates attachment forces were more than 10 times higher than on smoother substrates and larvae were able to endure the highest flow velocities in the flume on both biofilm-covered and biofilm-free substrates. Consequently, biofilm is of important ecological relevance for the larvae not only as food source, but also as a factor influencing their attachment ability in natural stream habitats.