Laboratory experiments using small artificial streams were performed on 3rd–5th instars of the net-spinning caddisflies Hydropsyche sparna (Ross), H. betteni Ross, H. morosa (Hagen), and H. slossonae (Banks) to examine behavioral responses after exposure to sand particles ranging from 126 to 2,000 μm in diameter. Sediment loads up to 14.6 kg/m2 were applied. When buried, the insects drifted, died, or remained “buried-alive.” When buried-alive, the larva remained in contact with its retreat and extended head, thorax, and anterior abdomen into the overlying water. Drift predominated when particle diameters were below 1,000 μm. Larger particles induced the buried-alive behavior. Mortality rates varied from 0 to 4.8%. Behavioral response to deposited sediment was similar in 3rd, 4th, and 5th instars. Larvae of H. betteni, H. morosa, and H. slossonae exhibited similar behaviors to H. sparna. The buried-alive behavior may represent an adaptation to frequent exposure to bedload sediment transport. Bedload sediment transport of the duration and magnitude studied is either a lethal or a sublethal disturbance, depending on the sediment particle size.
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