Investigating the threat to Sitka spruce from Ips typographus: discrimination and colonization of Britain's principal commercial conifer by a damaging forest pest.

backgroundIps typographus (L.), the eight-toothed spruce bark beetle (Coleoptera: Scolytinae), has devastated European Norway spruce (Picea abies) forests in recent years. For the first time, I. typographus has established localized breeding populations in Britain, where Sitka spruce (P. sitchensis) is a critical component of plantation forestry. The interactions between Norway spruce and I. typographus are well understood, but relatively little is known about the susceptibility of Sitka spruce to the beetle. This study aimed to determine whether I. typographus would select Sitka, compared to Norway spruce, as a host for breeding, and to study the chemical ecology underlying these host preferences.

resultsHost choice assays were conducted in the laboratory using freshly cut spruce logs, and then verified in the field in an area with an endemic population of I. typographus. Overall, colonization and breeding success were found to be similar in cut Sitka and Norway spruce material. The response of I. typographus, reared on both Norway and Sitka spruce, to headspace extracts of aged and fresh Norway and Sitka spruce material was tested behaviorally using four-arm olfactometry. Odors of aged wood from the two species were equally attractive, and fresh Sitka was more attractive than fresh Norway spruce. Antennal responses to Norway Spruce and Sitka Spruce headspace extracts were located using GC-EAG and identified by coupled GC-mass spectrometry and GC co-injection with authentic standards. Norway- and Sitka spruce-reared beetles did not differentiate between synthetic Norway or Sitka spruce blends and responded similarly.

conclusionThese findings suggest I. typographus will select and colonize cut Sitka as readily as cut Norway spruce, with implications for its establishment risk in Sitka-growing regions. Whilst the susceptibility of live Sitka trees remains unclear, the study advances the understanding of the role of both host-emitted volatile organic compounds (VOCs) in primary host location and induced host preference in host selection by I. typographus. © 2025 Crown copyright and The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. This article is published with the permission of the Controller of HMSO and the King's Printer for Scotland.