Damselfly larvae learn to recognize predators from chemical cues in the predator's diet

Chemosensory recognition of predators by naive prey may be facilitated if the predator's diet chemically 'labels' the predator. In a laboratory experiment, behaviour patterns were quantified in individual damselfly larvae, Enallagma spp., that had never been exposed to pike, Esox lucius, before and after exposing the damselflies to one of three chemical stimuli: water from a tank that held pike fed a diet of (1) damselflies, (2) fathead minnows, Pimephales promelas, or (3) mealworms, Tenebrio molitor. Damselflies decreased their frequency of feeding bites, head bends and moves in response to stimuli from pike fed damselflies and pike fed fathead minnows, but not to stimuli from pike fed mealworms. Damselflies are sympatric with fathead minnows in the population tested, and probably have many of the same predators. A response to stimuli from pike fed fathead minnows indicates that damselflies associate predation risk with stimuli from injured minnows. In a second experiment, responses of damselflies previously exposed to stimuli from pike fed one of the three treatment diets (damselfly, fathead minnow or mealworm) were tested for a response to stimuli from pike fed mealworms. Damselflies that had been exposed to stimuli from pike fed damselflies or fathead minnows in the first experiment responded to stimuli from pike fed mealworms in the second experiment, but damselflies exposed to pike fed mealworms in the first experiment did not. Thus (1) pike-naive damselflies may initially respond to chemical stimuli from pike based on stimuli of conspecifics or familiar heterospecifics in the pike's diet, and (2) damselflies can learn to recognize chemical stimuli of pike irrespective of the pike's recent feeding regime based on the initial association with damselflies or minnows in the pike's diet. (C) 1996 The Association for the Study of Animal Behaviour