Schlyter, F., Birgersson, G., Byers, J.A., & Bakke, A. 1992.
The aggregation pheromone of Ips duplicatus and its role
in competitive interactions with I. typographus
(Coleoptera: Scolytidae). Chemoecology 3:103-112. pdf
Abstract--
Ips duplicatus with I. typographus co-inhabiting Norway spruce
(Picea abies (L.) Karst.) would benefit from a pheromone blend distinct
from that of the larger competitor I. typographus. GC-MS analysis showed
that I. duplicatus males feeding in the host produced ipsdienol (Id),
cis-verbenol (cV), trans-verbenol (tV), myrtenol (Mt), and E-myrcenol (EM)
and traces of 2-methyl-3-buten-2-ol (MB). I. duplicatus produced Id in approximately
racemic form (48.9-54.5% (+)-(S)-isomer). The amounts of Id and EM released
over a 9 day period had a maximum of 250 and 5 ng/h/male, respectively, on
day 2. Exposure of I. duplicatus males to myrcene and alpha-pinene resulted
in the production of small amounts of Id, cV, tV, Mt, and trans-pinocarveol, but
not of EM. In laboratory bioassays with walking beetles, the pheromone
component Id alone was weakly attractive while EM was inactive, but in
binary combination with Id strongly synergized attraction. A combination of
EM and Id at a release rate equivalent to 100-200 males was more attractive
in the field than 70 unmated males in a spruce log. The addition of myrcene
(a suggested pheromone precursor of Id) to Id did not enhance trap catches,
while addition of EM increased catches > 10-fold. Subtracting EM from a
blend of Id, EM, cV, MB drastically reduced trap catches while subtraction of
cV or MB or both had no significant effect. Addition of EM over a wide
concentration range to the synthetic pheromone of I. typographus did not
reduce the attraction of females of this species in the laboratory. A two-species
pheromone interaction field test releasing I. typographus pheromone
components (MB+cV) at 10-1000 male equivalents (ME) and I. duplicatus pheromone
(Id+EM) at 0, 10-1000 ME in all possible combinations showed both positive
intraspecific dos-response effects and an interspecific inhibition. Higher
release rates of EM appeared to inhibit I. typographus, especially males.
In a tree colonization model, the response of the two competing species to
their respective pheromones show a good separation during the mass-attack
with a small initial cross-attraction. It remains to be shown whether either
of the two pheromone systems have in fact evolved in the present sympatry,
or if they are an incidental effect of ancestry of these phylogenetically
distant Ips.
Chemical Ecology