Dynamical Effects of Plant Quality and Parasitism on Population Cycles of Larch Budmoth

Turchin, Peter; Wood, Simon N.; Ellner, Stephen P.; Kendall, Bruce E.; Murdoch, William W.; Fischlin, Andreas; Casas, Jérôme; McCauley, Edward; Briggs, Cheryl J.

doi:10.1890/0012-9658(2003)084[1207:deopqa]2.0.co;2

Cited by 141 publications

(154 citation statements)

References 27 publications

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“…Crucial additional support is also provided by differences in defoliation levels between forest types. Meanwhile, the lack of evidence that induced defenses affect other insects may be a consequence of the lack of large-scale variation in tree-species composition within forests attacked by those insects (11,26), rather than a true lack of effect of induced defenses. Given enough experimental data with which to estimate parameters, however, our models could in principle be used to detect effects of induced defenses in defoliation data even in the absence of variability in forest type.…”

Section: Discussionmentioning

confidence: 99%

“…Moreover, there are no obvious signs of the effects of induced defenses in time series of defoliation or insect densities. Induced-defense models therefore provide no better an explanation for defoliator cycles than do natural-enemy models (10,11), while additionally providing no explanation for mortality due to natural enemies. Given the successes of the natural-enemy hypothesis, these failures of the induced-defense hypothesis have led to the conclusion that induced defenses play little to no role in defoliator outbreak cycles (3).…”

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confidence: 96%

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Induced plant defenses, host–pathogen interactions, and forest insect outbreaks

Elderd

Rehill

Haynes

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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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 induceddefense models explain defoliation data no better than naturalenemy 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. host-pathogen model | Lymantria dispar | complex population dynamics | spatial model | hydrolyzable tannins P eriodic outbreaks of forest-defoliating insects severely damage valuable timber and increase atmospheric CO 2 levels by converting forests from carbon sinks to carbon sources (1). Decades of research have produced multiple hypotheses to explain defoliator outbreak cycles (2), but a decisive experiment to choose between competing hypotheses faces almost insurmountable logistical difficulties, because outbreaks occur at 5-30 y intervals and typically cover thousands of square kilometers (3). Efforts to support particular hypotheses have therefore instead relied on a mixture of observational field data, small-scale field and laboratory experiments, and mathematical models.For example, the most widely accepted hypothesis is that defoliator cycles are driven by natural enemies. Support for this hypothesis comes first of all from observational data showing that defoliators experience high rates of infection by specialist pathogens and parasitoids in peak populations (2, 4) and high rates of attack by generalist predators and parasitoids in trough populations (5). Second, experimental data have confirmed key assumptions of defoliator-natural-enemy models, and the models produce longperiod, large-amplitude cycles resembling time series of insect densities and defoliation levels (6).Neither data nor models have provided meani...

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 96%

Induced plant defenses, host–pathogen interactions, and forest insect outbreaks

Elderd

Rehill

Haynes

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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show abstract

“…Specifically, we start with an initial guess for the control at the first iteration. We then forward solve the state equations (22) and then backward solve the adjoint equations (24). Once these approximations are complete, we update the control by using the characterization (26) derived in Theorem 3.1.…”

Section: Numerical Examplesmentioning

confidence: 99%

“…Turchin et al [24] propose two discrete-time host-parasitoid models to investigate possible cycling mechanisms for the larch budmoth , Zeiraphera diniana, in the Swiss Alps. In these two models studied by Turchin et al, the Ricker type nonlinearity is used as the per capita moth growth rate.…”

Section: Introductionmentioning

confidence: 99%

Discrete-time host–parasitoid models with pest control

Jang

2012

Journal of Biological Dynamics

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“…This insect has an annual life cycle and spends the winter as an egg on the larch branches, starting to feed on the needles as soon as the bud breaks. Multiple factors seem to be in volved in triggering the cycles, such as the host plant quality, the natural en emies, and the migration of the moths (Baltensweiler & Rubli 1999, Bjornstad et al 2002, Turchin et al 2003. However, a disturbance probably related to climate change has caused the col lapse of an outbreak, which was started in 1989 in the traditional occurrence area in Upper Engadine Valley (Baltens weiler 1993).…”

Section: Zeiraphera Dinianamentioning

confidence: 99%

iForest - Biogeosciences and Forestry

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Dynamical Effects of Plant Quality and Parasitism on Population Cycles of Larch Budmoth

Cited by 141 publications

References 27 publications

Induced plant defenses, host–pathogen interactions, and forest insect outbreaks

Induced plant defenses, host–pathogen interactions, and forest insect outbreaks

Discrete-time host–parasitoid models with pest control

iForest - Biogeosciences and Forestry

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