Dataset Information

Induced plant defenses, host-pathogen interactions, and forest insect outbreaks.

ABSTRACT: Cyclic outbreaks of defoliating insects devastate forests, but their causes are poorly understood. Outbreak cycles are often assumed to be driven by density-dependent mortality due to natural enemies, because pathogens and predators cause high mortality and because natural-enemy models reproduce fluctuations in defoliation data. The role of induced defenses is in contrast often dismissed, because toxic effects of defenses are often weak and because induced-defense models explain defoliation data no better than natural-enemy models. Natural-enemy models, however, fail to explain gypsy moth outbreaks in North America, in which outbreaks in forests with a higher percentage of oaks have alternated between severe and mild, whereas outbreaks in forests with a lower percentage of oaks have been uniformly moderate. Here we show that this pattern can be explained by an interaction between induced defenses and a natural enemy. We experimentally induced hydrolyzable-tannin defenses in red oak, to show that induction reduces variability in a gypsy moth's risk of baculovirus infection. Because this effect can modulate outbreak severity and because oaks are the only genus of gypsy moth host tree that can be induced, we extended a natural-enemy model to allow for spatial variability in inducibility. Our model shows alternating outbreaks in forests with a high frequency of oaks, and uniform outbreaks in forests with a low frequency of oaks, matching the data. The complexity of this effect suggests that detecting effects of induced defenses on defoliator cycles requires a combination of experiments and models.

SUBMITTER: Elderd BD

PROVIDER: S-EPMC3773759 | biostudies-literature | 2013 Sep

REPOSITORIES: biostudies-literature

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Induced plant defenses, host-pathogen interactions, and forest insect outbreaks.

Elderd Bret D BD Rehill Brian J BJ Haynes Kyle J KJ Dwyer Greg G

Proceedings of the National Academy of Sciences of the United States of America 20130821 37

Cyclic outbreaks of defoliating insects devastate forests, but their causes are poorly understood. Outbreak cycles are often assumed to be driven by density-dependent mortality due to natural enemies, because pathogens and predators cause high mortality and because natural-enemy models reproduce fluctuations in defoliation data. The role of induced defenses is in contrast often dismissed, because toxic effects of defenses are often weak and because induced-defense models explain defoliation data ...[more]

PMID: 23966566

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Dataset Information

Induced plant defenses, host-pathogen interactions, and forest insect outbreaks.

Publications

Induced plant defenses, host-pathogen interactions, and forest insect outbreaks.

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