PARENT SESSION
Oral Session #18: Predator-Prey Interactions: Plants and animals. Presiding: B. Goodwin.
Monday, August 6, 2001. 1:00 PM to 5:00 PM. Hall of Ideas I.
Can chemical communication be cryptic? Adaptive responses of herbivores to natural enemies exploiting prey semiochemistry.
Raffa, Kenneth1, Aukema, Brian1, Erbilgin, Nadir1, Hobson, Kenneth1, 1
ABSTRACT- Many predators and parasites use chemical cues associated with herbivore feeding and mating to locate prey. We know relatively little, however, about possible mechanisms by which herbivores may avoid these natural enemies, particularly without reducing fitness. We investigated this issue using bark beetles (Scolytidae) which feed subcortically within conifers. Bark beetles use aggregation pheromones to attract mates and to collectively deplete host plant defenses. Adapted predators and parasites, particularly Cleridae, Histeridae, and Pteromalidae, use these pheromones to locate colonized trees, and have the potential to exert high mortality. We conducted field behavioral studies, which suggest that subtle shifts in the stereochemistry and additional components of scolytid pheromones, combined with variation in space and time, can provide herbivores with partial (and presumably temporary) escape, while maintaining the integrity of intraspecific communication. Natural enemies were strongly attracted to herbivore pheromones, but differed in their relative preferences for various components. The trap data suggest that predators that exploit semiochemical cues must track a more variable, complex, and dynamic signal than previously recognized. Laboratory predation experiments, reciprocal population exchange studies, host range assays, and selective breeding of pheromone traits within bark beetle populations, support this model of predator driven changes in herbivore communication systems. For example, beetles from specific regions and laboratory lineages experienced differential predation in controlled field studies. These results have implications to predator - prey coevolution, tritrophic relationships, and biological control.
KEY WORDS: predator prey interactions, coevolution , semiochemistry, bark beetles