Physical sensory ecology | Boln. Asoc. esp. Ent. 21 (Supl.): 79 | 1997
How caterpillars detect predatory paper-wasps - a case study in sensory ecology (with emphasís on the research methods used for unravelling an airmovement detector)
J. Tautz
ABSTRACT
Caterpillars of a number of butteifly and moth species are equipped with hair receptors that can be stiinulated by even weakest air movements. For the caterpillars ofBaraihra hrossicae (Noctuidae) it could be shown that stimulation of such hairs elicits behavioral reactions that help escaping predatory wasps. The adequate stimulus is a rhythmic air movement produced by the wingbeat of the approaching wasp. In the ´´arms race´´ between prey and predator the sensitivity of the caterpillars mechanoreceptive hair sensilla became optimised to the adequate stimulus and reach the limit that can be expected for such a system from theoretical considerations.
The investigation of the basis of such a communication system has to start from a behavioral analysis of the interaction between prey and predator. This way details of hunting and defense strategies are unravelled. As a result one gets a set of possible sensoiy modalities used by the prey for predator detection. Artificial application of each of these suspected stimuli reduces the list to those that do elicit the defense reactions. After identifícation of the adequate stimulus modality(ies) one has to search for the corresponding prey-sensilla. A quantitative analysis of the stimulus fleld produced by the sender (predator) and the physical and physiological properties of the sensilla in the receiver (prey) uncovers the degree of match between the sensory filter and the relevant signáis.
Such a research strategy was applied to the caterpillar/wasp-system and involved fíeld experiments (observation of an undisturbed system vs. manipulated caterpillars) to show the importance of the caterpillars hair receptors, biomechanical measurements (laser-Doppler-anemometry) to detennine details of the air movements produced by the wasp and the mobility of the hair sensilla (laser- Doppler-víbrometry), and electrophysiological experiments to detennine the filter properties of the sensory cells. A final synthesis shows the degree of match between stimulus and receptor.
The talk will go through each of these steps carefully with special emphasis on the options but aiso the limits of the research methods used.
