Antipredator behavior of Colorado potato beetle larvae differs by instar and attacking predator

To avoid capture by predators, herbivores often deploy predator avoidance or deterrence behaviors. Chemical defenses of Colorado potato beetles (CPB, Leptinotarsa decemlineata) have been described, but little is known about antipredator behaviors of CPB larvae in response to attack by generalist predators. We examined the behavioral responses of second, third, and fourth instar CPB larvae when contacted by predatory lady beetles (Hippodamia convergens) or damsel bugs (Nabis alternatus). Of these predators, only the damsel bug readily captures CPB larvae. First, in simple Petri-dish arenas we touched single CPB larvae with either a lady beetle or damsel bug adult attached to the end of a wooden dowel, or a bare dowel as a control. Larvae responded to predator contact by walking away, rearing up, regurgitating onto their ventral surface, wiggling their bodies, and/or defecating. The number of behavioral responses increased significantly when larvae were touched with a predator compared to a bare dowel, when larvae were in later instars, and when larvae were contacted by a damsel bug rather than a lady beetle. Next, we observed natural encounters between CPB larvae and predators on potato plants. We again found that fourth instar larvae were most likely to initiate antipredator behaviors, and that all larval stages reacted more intensely to damsel bugs than lady beetles. In summary, we found that CPB larvae deployed a complex suite of behaviors when accosted by generalist predators. The frequency of behavioral response varied by larval instar, and appeared to be scaled to the risk posed by the predator encountered. (C) 2010 Elsevier Inc. All rights reserved.