Herbivory by the weevil, Strophosoma melanogrammum, causes severalfold increase in emission of monoterpenes from young Norway spruce (Picea abies)

We measured monoterpene emission from young Norway spruce (Picea abies) in the laboratory with a static flow chamber technique. The compounds α-pinene, β-pinene, and camphene dominated the emission. We added two species of needle-eating weevils, Strophosoma melanogrammum and Otiorhynchus sp., to the spruce trees. In two separate experiments with 3 or 2 yr old trees, addition of 16 or 14 Strophosoma melanogrammum per tree increased monoterpene emission from 400 ng tree−1 h−1 to a maximum of 2900 ng tree−1 h−1, and from 65 ng tree−1 h−1 to a maximum of 1300 ng tree−1 h−1, respectively. Addition of Otiorhynchus sp. did not affect monoterpene emission. Addition of one individual of Strophosoma melanogrammum induced a three-fold increase in monoterpene emission. The response to Strophosoma melanogrammum lasted for several weeks. Weevil attack did not change the concentration or composition of monoterpenes in the needles indicating that the trees relied primarily on a constitutive defence. The amount of monoterpenes stored in the needles could sustain the highest emission rates measured for 7.3 months.