Bark beetle, Pityogenes chalcographus (order Coleoptera: family Scolytidae)
walking on the bark of Norway spruce (Picea abies). The light green needles are from spruce but only half grown since this
picture was taken in May in Värmland (middle) Sweden. This beetle is rather small for bark beetles, being only
2 mm long and weighing only 1.2 mg (379,000 per pound). Pityogenes chalcographus
ranks among the two most important killers of spruce in Europe. The beetles often cause severe damage to young,
Christmas-tree sized stands of spruce. The beetles are attracted to
pheromone from feeding males, which consists of two chemicals, chalcogran and methyl decadienoate. Chalcogran was
discovered in 1977 and was shown to attract some beetles but not as well as a spruce log infested
with beetles. In 1988, methyl decadienoate was discovered which together with chalcogran
could attract about 35 times more beetles than chalcogran alone. Methyl decadienoate released alone did not
attract any beetles at all. This is a good example of "synergism" between compounds, where the combination
is much more biologically potent than either compound presented
alone.
Methods for isolating synergistic compounds using behavioral bioassays can be found in the
following
image (C) 1995 by John A. Byers