Successful reproduction and pheromone production by the spruce bark beetle in evolutionary naïve spruce hosts with familiar terpenoid defences

The European spruce bark beetle Ips typographus is a damaging pest on spruce in Europe. Beetle interactions with tree species originating outside the natural range of the beetle are largely unknown and may be unpredictable because trees without a co‐evolutionary history with the beetle may lack effective defences. The terpenoid composition and breeding suitability for I. typographus of the historic host Norway spruce Picea abies were compared with two evolutionary naive spruces of North American origin that are extensively planted in North‐West Europe: Sitka spruce Picea sitchensis and Lutz spruce Picea glauca x lutzii. The bark of all three species had a similar chemical composition and similar levels of total constitutive terpenoids, although Norway spruce had higher total induced terpenoid levels. Beetles tunnelling in the three spruce species produced similar amounts of aggregation pheromone. Controlled breeding experiments showed that I. typographus could produce offspring in all three species, with a similar offspring length and weight across species. However, total offspring production was much lower in Sitka and Lutz spruce. Overall, the results of the present study suggest that I. typographus will be able to colonize Sitka and Lutz spruce in European plantations and in native spruce forests in North America if introduced there.