Byers, J.A., Birgersson, G., and Francke, W. 2013. Aggregation pheromones of bark beetles, Pityogenes quadridens and P. bidentatus, colonizing Scotch pine: olfactory avoidance of interspecific mating and competition.
Chemoecology 23:251-261.
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Abstract--
The bark beetles Pityogenes bidentatus and
Pityogenes quadridens (Coleoptera, Curculionidae, Scolytinae)
are sibling species that feed and reproduce in bark
areas on branches of Scotch pine, Pinus sylvestris. To
identify aggregation pheromone components of both species,
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 or more. In the field in southern Sweden, grandisol and
(4S)-cis-verbenol were weakly attractive alone 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 2 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 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. Our results suggest
that aggregation pheromone components from males
of each species not only attract conspecifics but also aid
individuals in avoiding interspecific mating and competition
for food and spatial resources within the bark phloem
layer.
Chemical Ecology