The Importance of Monoterpenes in the Aggregation of the Spruce Bark Beetle Ips typographus (Coleoptera: Scolytidae: Ipinae)

Abstract

Field bioassays show that the aggregation of the spruce bark beetle Ips typographus (Linnaeus 1758) to pheromone baited traps is affected by monoterpenes. The mixture of (-)-α-pinene and (+)-limonene attracts the adults significantly (2 ml of each compound per dispenser) whereas the individual components are ineffective. The application of (-)-β-myrcene reduces the trap catch to 33%. (+)-α-pinene acts as a repellent; only 6% of the trap catch of the control can be observed. The last-mentioned compound inhibits the colonization of trap trees by 1 typographus. Trap trees felled in winter can be devided in two groups with regard to the colonization by I typographus: (1) Uninfested trees are found to have only small amounts of monoterpenes in the inner bark which decrease only little in the interval between the date of felling and the dispersal of the beetles. (2) Trees which are colonized have higher concentrations of terpenes in the bast which are diminished significantly until I typographus initiated the brood systems. But the amounts of monoterpenes in the inner bark of colonized trap trees are higher compared to those which remain uninfested. I typographus is found to colonize parts of the stem which are characterized by an optimum concentration of the key monoterpene (-)-α-pinene ranging between 0.08 - 0.35 nmol/mg fresh matter. The density of brood systems correlates with an index value which is calculated from the concentrations of (-) and (+)-α-pinene, (+)-limonene, and (-)-β-myrcene.