Visual and mechanical cues used for prey detection by the larva of Libellula depressa (Odonata Libellulidae)

Cues used for the detection of prey by the larva of Libellula depressa (Odonata Libellulidae) were investigated. Nymphs (alive and recently dead) of the mayfly Cloeon dipterum (Ephemeroptera Baetidae) and dummies were used as prey models. The responses of the larva to stimulations of different kinds and intensity, in different areas around the body, were tested in the laboratory in six different behavioural experiments. From the statistical analysis of the data (Pearson Chi-square and one-way ANOVA) it emerged that: (i) chemical cues seem not to be involved in the detection of the prey or, if they are involved, they are negligible in comparison with other kinds of stimuli; (ii) the larva of L. depressa utilizes mechanical and visual cues for the release of the predatory labial strike, and either one of these cues is effective for labial strike elicitation; (iii) mechanical stimuli have a predominant role in predation; (iv) the larva of L. depressa can rely on a non-contact mechanical sense for the detection of the prey. The importance of mechanical and visual cues is discussed in relation to the pond bed habitat of this species.