Chemically mediated predator-free space: Herbivores can synergize intraspecific communication without increasing risk of predation

Natural enemies of herbivores often locate cryptic insects by responding to volatiles associated with the prey's feeding and mating. For example, predators of bark beetles (Coleoptera: Scolytidae) exploit the aggregation pheromones that their prey use to attract mates and secure hosts. Bark beetles are cryptic insects that feed and develop in the subcortical tissues of trees and spend all but a portion of their life history within this habitat. The pine engraver, Ips pini, produces the pheromone ipsdienol throughout its transcontinental range. Predators of I. pini exploit this chemical as a kairomonal cue. Eastern and Midwestern I. pini populations also produce lanierone, which synergizes their attraction to ipsdienol. We evaluated the effects of varying amounts of lanierone, in combination with a constant amount of racemic ipsdienol, on the relative attraction of I. pini and its major predators in Wisconsin. Higher numbers of I. pini were captured with increasing release rates of lanierone. In contrast, the numbers of the major predators, such as Thanasimus dubius, Enoclerus nigrifrons, Platysoma cylindrica, and P. parallelum, did not differ among different lanierone release rates. The response of I. pini but not their predators to lanierone at ecologically realistic release rates may be part of a coevolving interaction between predators and prey and offers new strategies for semiochemically based pest management by selectively removing pests and leaving predators.