Nonlethal Effects of Predation: Presence of Insectivorous Birds Affects the Behaviour and Level of Stress in Insects

AbstractInsect exposure to their predators can affect individuals and community processes, through direct consumption or nonlethal effects. However, the links between behavioural and physiological responses and stimuli needed for the development of fear are not clear. We subjected the desert locusts (Schistocerca gregaria) to three nonlethal treatments, using the great tits(Parus major)as a potential predator. The treatments involved: (1)bird- presence of a great tit and its calls, (2)call- great tit calls only, (3)control- without any treatment. In the first behavioural laboratory experiment, locusts were offered food and shelter in an open space. The duration of hiding and feeding indicated fear responses. In the second laboratory experiment with the same three treatments, levels of the adipokinetic hormone (AKH) were evaluated in the central nervous system (CNS) and haemolymph. In the third experiment in an outdoor aviary, birds were further away from locusts before we measured physiological response. In the first experiment, the locusts were hiding for significantly longer and feeding for a shorter time during bird treatment than during the call or control treatments. The proximity of birds to locusts in the laboratory experiment elicited a significant increase in the AKH levels in the CNS and haemolymph as compared to the call/control treatments. The outdoor experiment confirmed the results for levels of AKH in CNS but not haemolymph. The proximity of predators, but not only their call, affected both behavioural and physiological responses of locusts.