Mechanisms of filter feeding in immature Simulium bivittatum Malloch (Diptera: Simuliidae) and Isonychia campestris McDunnough (Ephemeroptera: Oligoneuriidae)

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Abstract
Immatures of Isonychia campestris McDunnough and Simulium bivittatum Malloch, fed mixtures of six size classes of polystyrene particles, captured particles that were smaller than the pore spaces between filtering structures more efficiently than was expected if filters functioned only as mechanical sieves. Capture efficiency was highest for the smallest (0.5 – 5.7 μm) particles. Relative efficiencies of filters for capturing suspended particles by four aerosol filtration mechanisms show that interception and diffusive deposition are mechanisms by which smaller particles reach the filter surface. The latter mechanism is a better predictor of size distribution of 0.5- to 5.7-μm particles captured by both insects. Adhesion of particles to filtering structures is probably by hydrophilic–hydrophobic or ionic interaction between particles and filters.