Predation and avoidance of tough leaves by aquatic larvae of the moth Parapoynx rugosalis (Lepidoptera: Pyralidae)

Aquatic larvae of the pyralid moth Parapoynx rugosalis Möschler repeatedly construct protective cases by cutting portions (discs) from leaves of the waterlily Nymphaea ampla and sandwich themselves between the disc and the underside of the host leaf. Construction of a new case requires leaving the old case, thus increasing exposure to predators and parasites. In an experiment, larvae with protective cases experienced no mortality due to predation by fish, whereas larvae without cases experienced substantial predation. In a series of choice tests, larvae preferentially selected young, tender leaves over old, tough leaves for construction of cases, and larvae spent significantly less time completing their shelters when cutting discs from young, tender leaves. A partial explanation of why larvae select young, tender leaves for construction of their protective shelters may be that exposure time to predators during construction is minimized. The same mechanism linking preferences for tender leaves to reduced exposure to predators during construction may also apply to other insect herbivores exhibiting leaf‐rolling or case‐building behaviour.