ALLELOCHEMIC ACTIVITY OF AGGREGATION PHEROMONES BETWEEN THREE SYMPATRIC SPECIES OF AMBROSIA BEETLES (COLEOPTERA: SCOLYTIDAE)

Abstract

Field experiments tested lineatin, the aggregation pheromone of Trypodendron lineatum (Olivier), in combination with either S-(+)- or (±)-sulcatol, the pheromones of Gnathotrichus retusus (LeConte) and G. sulcatus (LeConte), respectively. Beetles of each species responded maximally to their own pheromone alone or in a binary combination. Slight, but significant cross attraction between Gnathotrichus spp. was evident, and G. retusus was slightly attracted to lineatin. Both Gnathotrichus spp., but not T. lineatum, responded to α-pinene with ethanol. These two compounds had no effect on the allelochemic activity of the pheromones. While mutually inhibitory communication would be of adaptive advantage in bark beetles which compete for an essentially 2-dimensional host, the phloem tissue, little selection pressure would occur among ambrosia beetles which share a more bountiful host, the 3-dimensional sapwood; hence the lack of mutual inhibition between Gnathotrichus spp. and T. lineatum. On the other hand, enantiomer-based specificity in pheromone communication between Gnathotrichus spp. may have been at least a partial basis for speciation. Compatibility of lineatin with either S-(+)- or (±)-sulcatol indicates that in pheromone-based pest management, 2-binary pheromone stimulus release systems can be used instead of 3 single ones.