The effects of α-pinene on the feeding performance and pheromone production of Dendroctonus valens

Herbivorous insects exploit multiple plant cues to detect and orient toward suitable hosts and, accordingly, hosts have evolved complex constitutive and inducible defenses in response. In China, the red turpentine beetle, Dendroctonus valens LeConte (Coleoptera: Curculionidae: Scolytinae), an invasive bark beetle from North America, attacks mainly Pinus tabuliformis Carriere (Pinaceae), which contains many monoterpenes. In this study, we explored how the monoterpene -pinene affects the feeding performance and pheromone production of D.valens. First, the composition and quantities of monoterpenes of both P.tabuliformis healthy trees and fresh stumps were determined and the infestation of D.valens in healthy trees and fresh stumps was investigated, linking the amount of monoterpenes and D.valens infestation. Gas chromatography-mass spectrometry (GC-MS) analysis showed that P.tabuliformis mainly contained -pinene, with concentrations of 0.1 and 0.5mgg(-1) in healthy pine phloem and stump phloem, respectively. Second, the monoterpene's influence on feeding performance was tested using phloem media with -pinene concentrations ranging from 0 to 30mgg(-1). The results showed that the percentages of beetles boring and the gallery lengths of both adult females and larvae were negatively correlated with the -pinene concentration although body weight changes did not correlate with -pinene concentration. Finally, pheromone analysis showed that the production of all pheromones increased with increasing -pinene concentrations. This study showed the dual effects of -pinene on D.valens: -pinene inhibited the bark beetle's feeding activities and in turn the bark beetle made use of it to produce pheromones. Our study indicated the importance of promptly removing fresh stumps in the field for the management of the bark beetle.