Net‐Spinning byAmphipsyche senegalensisLarvae (Trichoptera: Hydropsychidae) in Lake Kariba (South Central Africa)

Abstract

Net‐spinning larvae of the hydropsychid Amphipsyche senegalensis Brauer are commonly found on submerged trees in exposed regions of Lake Kariba as well as in nearby rivers. Final instar larvae were removed from the lake, placed into a laboratory stream channel and the nets compared with those spun by larvae in Kariba. No significant differences were found in mean mesh size between nets from the channel (44 × 34 μm) and those from the lake (48 × 40 μm). The width of the silk strands used in net building varied from 1.5–3.2 μm, but strand width differences between nets from the two habitats were not statistically significant. However, nets spun by A. senegalensis larvae in nearby rivers were in marked contrast to those built by larvae from Kariba. A final instar net had a mean mesh size of 77 × 67 μm and a mean silk strand diameter of 7.1 μm, while a net from a younger instar measured 54 × 47 μm with a mean silk strand width of 3.6 μm, indicating that flow regime may play a part in influencing net construction. Data for all A. senegalensis nets examined showed a positive correlation between mesh size and silk strand diameter (P < 0.001). It is suggested that the apparent flexibility in net‐spinning behaviour may assist in adapting larvae to the fluctuating flow conditions often associated with lotic habitats.