Early resistance of alien and native pines against two native generalist insect herbivores: no support for the natural enemy hypothesis
Article first published online: 21 NOV 2011
© 2011 The Authors. Functional Ecology © 2011 British Ecological Society
Volume 26, Issue 1, pages 283–293, February 2012
How to Cite
Carrillo-Gavilán, A., Moreira, X., Zas, R., Vilà, M. and Sampedro, L. (2012), Early resistance of alien and native pines against two native generalist insect herbivores: no support for the natural enemy hypothesis. Functional Ecology, 26: 283–293. doi: 10.1111/j.1365-2435.2011.01931.x
- Issue published online: 18 JAN 2012
- Article first published online: 21 NOV 2011
- Received 25 February 2011; accepted 27 September 2011 Handling Editor: Alison Brody
- condensed tannins;
- Hylobius abietis;
- induced defences;
- non-volatile resin;
- plant invasions;
- plant–herbivore interactions;
- Thaumetopoea pityocampa
1. The natural enemy hypothesis (NEH) predicts that alien plant species might receive less pressure from natural enemies than do related coexisting native plants. However, most studies to date are based on pairs of native and alien species, and the results remain inconclusive. The level of attack by native generalist herbivores can vary considerably between plant species, depending on defensive traits and strategies. Plant defences include preformed constitutive and induced defences that are activated as plastic responses to herbivore attack. However, the efficacy of induced defences could be altered when alien species entering an area are exposed to native enemies.
2. We tested the NEH for several closely related alien and native pines to Europe by examining early anti-herbivore resistance to damage by two generalist native insect herbivores (Hylobius abietis and Thaumetopoea pityocampa); the differences in constitutive and inducible chemical defences (i.e. non-volatile resin and total phenolics in the stem and needles); and whether consumption preferences shift after induced defences have been triggered by real herbivory.
3. We did not find alien pines to be less damaged by two generalist herbivores than native pines were. The constitutive concentration of chemical defences significantly differed among pine species. The concentration of constitutive total phenolics in the stem was greater in native than in alien pines. The opposite trend was found for constitutive total phenolics in the needles. The concentration of chemical defences (non-volatile resin and total phenolics) in the stem significantly increased after herbivory by H. abietis. Moreover, the induction of total phenolics by H. abietis damage was significantly greater in native pine species than in alien pines. On the other hand, only concentrations of non-volatile resin in needles significantly increased after herbivory by T. pityocampa, but without significant differences in inducibility between alien and native pines. In cafeteria bioassays, H. abietis consumed the twigs from alien more than those from native species irrespective of prior exposure to the insect. Meanwhile, no differences among range origin were found in the T. pityocampa cafeteria bioassays.
4. Overall, we found no support for the NEH in alien pines to Europe. This suggests that alien pines, in regions where they coexist with native congeners, may be controlled by native generalist herbivores, this being one reason that invasion by alien pines is not frequent in Europe.