Visual Cues Can Alter the Behavioural Responses of Dragonfly Larvae to Chemical Alarm Cues

Chemical alarm cues are widely used across ecosystems to detect predators and reduce predation risk, but in cannibalistic species, these cues may also convey information about conspecific diet. However, the sensory mechanisms that governs the trade‐off between antipredator and predatory behavioural strategies are poorly understood. In this study, we investigated how visual and chemical alarm cues influence the spread of risk‐related information in Aeshna cyanea larvae, a widespread odonate with frequent cannibalistic interactions among early instars. Using a controlled experimental design, we aimed to isolate the effects of chemical and visual stimuli on antipredator behaviour and assess whether such information can be socially transmitted among spatially proximate conspecifics. We found that exposure to chemical cues from injured conspecifics significantly reduced locomotor activity in most demonstrators, i.e., individuals directly exposed to the alarm cues. However, this effect was modulated by the visual detection of conspecifics: observer 1 individuals showed no activity change when visual cues on nearby demonstrators were present, but increased activity when chemical cues were presented alone. Moreover, visual contact between demonstrators and observer 1 larvae consistently reduced inter‐individual distance, regardless of the presence of chemical cues. In contrast, observer 2 individuals, who only received visual cues from observer 1 larvae, showed no behavioural change. These results indicate that while A. cyanea larvae do not copy the antipredator behaviour of conspecifics, visual cues modulate responses to chemical information, supporting a role for context‐dependent cue integration in decision‐making in a non‐grouping, cannibalistic species.