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.abstract
Methods for isolating synergistic compounds using behavioral bioassays can be found in the followingabstract
image (C) 1995 by John A. Byers