INTERACTION BETWEEN CHEMICAL AND TACTILE CUES IN MAYFLY DETECTION OF STONEFLIES

1. Behavioural experiments were performed in artificial stream channels to determine if nymphs of the mayfly Paraleptophlebia adoptiva (Ephemeroptera: Leptophlebiidae) respond to (i) chemical cues from stonefly nymphs, (ii) chemical cues from disturbed conspecific mayflies, and (iii) body fluids of injured conspecifics, and (iv) whether responses to these chemical cues are different when combined with contact by foraging Acroneuria carolinensis stonefly nymphs (Plecoptera: Perlidae). 2. Although none of the chemical cues elicited changes in mayfly behaviour in the absence of predator contact, stonefly chemical cues significantly enhanced the avoidance response of mayflies to stonefly contact. Mayfly nymphs swam more frequently and crawled further in response to predator encounters when chemical cues were present than when chemical cues were absent. Thus, direct stonefly precontact chemical cues appear to sensitize P. adoptiva to the potential for an encounter with A. carolinensis, enabling stronger escape or avoidance responses upon contact. 3. Mayfly chemical cues that provide indirect information about the proximity of a predator (disturbed or injured conspecifics) did not stimulate increased mayfly response to stonefly contact. Indirect cues may provide less reliable information about the proximity of a stonefly than chemicals emitted directly from an adjacent predator. Mayflies might use chemical cues only in the presence of predator contact because of the high cost of premature escape in a running water system.