Antipredator Responses and the Perception of Danger by Mosquito Larvae

Abstract

I conducted a series of laboratory experiments to contrast the responses of two species of mosquito larvae to a common predator, the freshwater bug Notonecta undulata. One prey species, Culex pipiens, commonly co—occurs with Notonecta, whereas the other, Aedes aegypti, shares no evolutionary history with this predator. I tested the evolution—based prediction that Culex should be killed at a lower rate due to stronger and more precise antipredator responses. I then studied the types of cues used by these prey to gauge predation risk by examining prey responses to simple disturbances and to potential chemical cues associated with predation. The results were that (1) both mosquito species responded to Notonecta by moving less and by shifting their microhabitat use; (2) Culex was indeed killed at a lower rate; (3) Culex showed far stronger responses to notonectids; (4) the response of Culex was correlated with actual predation risk even after encounter rate with predators was accounted for; and (5) Culex, but not Aedes, responded to water in which conspecifics had been preyed upon by Notonecta. The differences in the responses of the two species can be explained by a fundamental difference in the way in which they estimate predation risk. Whereas the behavior of Aedes can be understood as a response to disturbance per se, Culex behavior is also mediated by chemical cues associated with the actual predation act. Since more predation on Culex should produce more alarm chemical, this cue is probably responsible for the observed "precise" (i.e., correlated with risk) responses.