Location: Pest Management and Biocontrol Research
Title: Aggregation pheromones of bark beetles, pityogenes quadridens and P. bidentatus, colonizing scotch pine: olfactory avoidance of interspecific competition Authors
|Birgersson, Goran -|
|Francke, Wittko -|
Submitted to: Chemoecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 21, 2013
Publication Date: N/A
Interpretive Summary: The bark beetles, Pityogenes bidentatus and P. quadridens, both attack and damage young trees of Scotch pine by tunneling in the inner bark. When bark beetles colonize a tree, early-arriving males release volatile chemicals (aggregation pheromone) that attract other beetles. However, beetles of these two species are seldom found in high numbers on the same bark areas of the tree. This suggests the aggregation pheromone of one species may signal beetles of the other species that the bark is already occupied. Extracts of beetles, combined with laboratory and field assays, indicated the main components of P. bidentatus aggregation pheromone were grandisol and (S)-cis-verbenol, whereas the aggregation pheromone of P. quadridens was identified as chalcogran and E-grandlure 2. Field tests also showed that grandisol (from P. bidentatus) reduced attraction of P. quadridens to its aggregation pheromone, whereas E-grandlure 2 and chalcogran (from P. quadridens) reduced response of P. bidentatus to its aggregation pheromone. These results indicate that aggregation pheromone components from the two species inhabiting the same host tree areas may aid the beetles in avoiding competition for limited resources represented by the inner bark. Identification of the aggregation pheromones of P. bidentatus and P. quadridens provides a basis for the development of trapping systems to monitor population levels during the spring flight season.
Technical Abstract: The bark beetles Pityogenes bidentatus and P. quadridens (Coleoptera, Curculionidae, Scolytinae) compete for bark areas on branches of Scotch pine, Pinus sylvestris. Hindguts and head/thoraxes of males and females of both species feeding in hosts were extracted in pentane and analyzed by gas chromatography and mass spectrometry. Hindguts of male P. bidentatus contained grandisol as the major component along with small amounts of (4S)-cis-verbenol and other monoterpenes. Dose-response bioassays in the laboratory showed the components were attractive at 0.2 ng/min to walking beetles from a distance of >=25 cm. In the field in southern Sweden, grandisol and (4S)-cis-verbenol were weakly attractive when released at rates of 0.05 and 0.5 mg/day, respectively, from a slow-rotating trap pair. Catch increased 3.6 to 13-fold when the two components were released together. The male proportion of the catch was 0.8 early in the flight period, declined to 0.5 on the peak flight day, and then declined further during the next two weeks to 0.2 on the last day of the flight period. Hindguts of male P. quadridens contained (2S,5R)- and (2S,5S)-chalcogran, as well as (E)-2-(3,3-dimethylcyclohexylidene)ethanol (E-grandlure 2) and E/Z-mixture of 2-(3,3-dimethylcyclohexylidene)acetaldehyde (grandlures 3 and 4), while female hindguts had only a trace amount of chalcogran. Laboratory studies proved E-grandlure 2 is an essential pheromone component for P. quadridens. Field bioassays with a slow-rotating trap pair in which the attractiveness of blends containing various candidate components were systematically compared with that of less complete mixtures, showed that chalcogran and E-grandlure 2 were synergistic aggregation pheromone components of P. quadridens. Field tests also showed that grandisol (from P. bidentatus) reduced attraction of P. quadridens to its aggregation pheromone, whereas E-grandlure 2 and chalcogran (from P. quadridens) reduced response of P. bidentatus to its aggregation pheromone. These results indicate that aggregation pheromone components from the two species inhabiting the same host tree areas may aid individuals in avoiding interspecific competition for food and spatial resources within the bark phloem layer.