MIXED MESSAGES ACROSS MULTIPLE TROPHIC LEVELS: THE ECOLOGY OF BARK BEETLE COMMUNICATION SYSTEMS.

Kenneth F. Raffa
Department of Entomology, University of Wisconsin, Madison, WI 53706USA

Bark beetle pheromones have proven useful models for understanding insectsemiochemistry, over several decades. However our understanding ofhow these signals function under natural conditions has evolved significantlyover this period. For example, the chemical signals that emit frombeetles on selected trees to flying beetles are modified by microorganisms,the host plants themselves, and canopy architecture. Beetle pheromoneswere originally viewed as rather uniform signals, that attracted mates,or coordinated “mass attacks”. Thus, a high level of emphasis wasplaced on the fidelity and consistency of these signals. Under naturalconditions, however, bark beetles are confronted with multiple, and oftenconflicting, selective pressures. To reproduce successfully, beetlesmust avoid or overcome host resistance mechanisms, minimize intraspecificcompetition, avoid interspecific competitors, and escape predation. Optimizing these various pressures requires contending with a number oftrade-offs, including one between the clarity and the diversity of thesignal. For example, variations in minor nuances in pheromonal signalscan offer one avenue for reducing the likelihood of predation, while atthe same time maintaining intraspecific functionality. Intraspecificvariation in bark beetle semiochemistry occurs among the pheromone chemicalstructures, spatially, temporally and various interactions. Pheromonesignaling appears to function differently at different population densities,and so may be both responsive and contributing to eruptive population behavior.