Feeding behaviour of predatory larvae of Atherix lantha Webb (Diptera: Athericidae)

Larvae of Atherix lantha Webb (Diptera: Athericidae) are piercing – sucking predators. Predator–prey experiments were conducted in beakers containing gravel substrates and airstone-oxygenated water. The predator:prey ratio used in all experiments was 5:5. One prey type was tested at a time. Prey tested included large and small heptageniid mayflies, hyalellid amphipods, and hydropsychid caddisflies. The effect of predator size was examined using two size classes of A. lantha larvae. Large A. lantha consumed more mayflies than did small A. lantha. However, amphipod mortality was the same with large as with small A. lantha. The effect of prey size on predation success was tested using two size classes of mayflies. Statistically, small A. lantha fed on equal numbers of small and large mayflies, whereas large A. lantha consumed more large than small mayflies. Data for species-wise comparisons are only available for small A. lantha; according to our results, hydropsychid caddisflies (average mortality (m) = 0.5346) are more vulnerable to predation than are hyalellid amphipods (m = 0.2041) and heptageniid mayflies (m = 0.1135–0.1813). However, the mortality of large mayflies caused by large A. lantha larvae (m = 0.5375) is the same as that of caddisflies caused by small A. lantha larvae. Thus, the vulnerability of prey species depends, in part, on predator size.