Abstract

Background: Tree-killing bark beetles (Coleoptera, Scolytinae) are among the most economically and ecologically important forest pests in the northern hemisphere. Induction of terpenoid-based oleoresin has long been considered important in conifer defense against bark beetles, but it has been difficult to demonstrate a direct correlation between terpene levels and resistance to bark beetle colonization.Methods: To test for inhibitory effects of induced terpenes on colonization by the spruce bark beetle Ips typographus (L.) we inoculated 20 mature Norway spruce Picea abies (L.) Karsten trees with a virulent fungus associated with the beetle, Ceratocystis polonica (Siem.) C. Moreau, and investigated induced terpene levels and beetle colonization in the bark.Results: Fungal inoculation induced very strong and highly variable terpene accumulation 35 days after inoculation. Trees with high induced terpene levels (n = 7) had only 4.9% as many beetle attacks (5.1 vs. 103.5 attacks m(-2)) and 2.6% as much gallery length (0.029 m m(-2) vs. 1.11 m m(-2)) as trees with low terpene levels (n = 6). There was a highly significant rank correlation between terpene levels at day 35 and beetle colonization in individual trees. The relationship between induced terpene levels and beetle colonization was not linear but thresholded: above a low threshold concentration of similar to 100 mg terpene g(-1) dry phloem trees suffered only moderate beetle colonization, and above a high threshold of similar to 200 mg terpene g(-1) dry phloem trees were virtually unattacked.Conclusion/Significance: This is the first study demonstrating a dose-dependent relationship between induced terpenes and tree resistance to bark beetle colonization under field conditions, indicating that terpene induction may be instrumental in tree resistance. This knowledge could be useful for developing management strategies that decrease the impact of tree-killing bark beetles.

Keywords

Ips typographus; granbarkborre; Ceratocystis polonica; Picea abies; terpene; Fungal inoculation; Induced defence

Published in

PLoS ONE
2011, Volume: 6, number: 10, article number: e26649
Publisher: Public Library of Science

SLU Authors

• Björklund, Niklas

  • Department of Ecology, Swedish University of Agricultural Sciences
    

• Långström, Bo

  • Department of Ecology, Swedish University of Agricultural Sciences
    

Associated SLU-program

Forest


UKÄ Subject classification

Forest Science


Publication identifier

DOI: https://doi.org/10.1371/journal.pone.0026649

Permanent link to this page (URI)

https://res.slu.se/id/publ/35774