Age specific behavioral responses of odonate larvae to chemical and visual cues from predators

Many aquatic organisms possess the ability to detect and respond to visual and chemical cues from predators and injured conspecifics, but relatively few studies have investigated if those responses change during development in odonates. In a laboratory experiment, I exposed 8th and 12th instar larvae of the dragonfly Anax junius to (1) the presence of a free-swimming fish predator (Lepomis macrochirus); (2) water that recently contained L. macrochirus; (3) water that contained crushed conspecifics; (4) water that recently contained living conspecifics; and (5) charcoal filtered tap water that contained no visual or chemical stimuli. The 12th instar A. junius moved more often, spent more time moving and spent less time perched on artificial aquatic vegetation than did 8th instar A. junius. A. junius moved less in the presence offish chemical cues relative to the control. Although 8th and 12th instar A. junius differed in their responses to stimuli from predators, the overall response of A. junius to predators was not strong. The characteristic high activity level of A. junius, which is an advantage in fishless habitats, may limit success of this species in habitats with insectivorous fish.