Antipredator responses of aphids to parasitoids change as a function of aphid physiological state

Under predation risk, prey may prioritize antipredator behaviours and sacrifice feeding. However, energetically constrained animals may choose to sacrifice or change antipredator responses and accept relatively greater risk in order to secure food. In this last case, the antipredator tactics chosen must balance safety and feeding in such a way that costs are minimized and benefits maximized. We studied the antipredator behaviour of pea aphid, Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae) subjected to different periods of food deprivation, against the parasitoid Aphidius ervi (Hymenoptera: Braconidae). As the energetic internal stress of aphids increased, the predominant antipredator response changed from walking away and dropping to kicking behaviour, and parasitization avoidance decreased. Parasitoids did not show preference between food-deprived and nonfood-deprived aphids. Dropping and walking away reduced parasitization from 50 to 33%. These results support the hypothesis that the antipredator behaviour of an aphid changes as a function of internal stress. By performing less costly behaviour such as kicking under energetically constrained conditions, aphids seem to minimize their probability of energy shortfall. Given that aphid antipredator behaviour is a function of nutritional state, its occurrence under natural conditions may match host quality spatial distribution. (C) 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.