Reversed Impacts by Specialist Parasitoids and Generalist Predators May Explain a Phase Lag in Moth Cycles: A Novel Hypothesis and Preliminary Field Tests

Klemola, Netta; Heisswolf, Annette; Ammunét, Tea; Ruohomäki, Kai; Klemola, Tero

doi:10.5735/086.046.0504

Cited by 25 publications

(38 citation statements)

References 52 publications

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“…Compensatory mechanisms, such as other groups of enemies acting on other life stages, may be the reason for this (Myers 1988). For instance, pupal and egg parasitoids have been reared from other samples of E. autumnata (Klemola et al. 2009).…”

Section: Discussionmentioning

confidence: 99%

Are population outbreaks in sub‐arctic geometrids terminated by larval parasitoids?

Schott

Hagen²,

Ims

et al. 2010

Journal of Animal Ecology

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Summary 1.Larval parasitoids (i.e. parasitoids attacking host larvae) constitute a major source of mortality in many ecologically and economically important forest insects, but how this mortality affects spatio-temporal population dynamics is often not clear. 2. In sub-arctic Fennoscandian birch forest, the two geometrids Epirrita autumnata and Operophtera brumata exhibit pronounced outbreak cycles with significant ecosystem impacts. As mortality owing to larval parasitoids often is very high, the hypothesis that parasitism terminates outbreaks has been advocated, but without decisive empirical evidence. 3. We analysed the altitude-and species-specific timing of population outbreaks typically seen in the coastal section of the sub-arctic birch forest ecosystem to evaluate the critical premise that parasitoid-inflicted larval mortality ought to predict geometrid population growth. 4. However, despite temporally high rates of parasitism, this did not influence the strongly speciesand altitude-patterned geometrid outbreaks. We therefore conclude that termination of cyclic outbreaks in these geometrids is caused by other regulatory mechanisms than larval parasitoids. 5. Regardless of their lack of effect on the altitude-specific outbreak dynamics, larval parasitoids accounted for some of the local spatial variance in the temporal dynamics. This implies that results from spatially localized observations and experiments, which dominate research on parasitoidhost interaction, may be misinterpreted with respect to their relevance for large-scale and longterm population dynamics.

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Section: Discussionmentioning

confidence: 99%

Are population outbreaks in sub‐arctic geometrids terminated by larval parasitoids?

Schott

Hagen²,

Ims

et al. 2010

Journal of Animal Ecology

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“…In O. brumata and E. autumnata the feeding period lasts for 4–8 weeks, depending on temperature and forage quality, after which they drop to the ground and pupate in the soil (Tenow, 1972; Bylund, 1999). The two species, when occurring in sympatry within their outbreak range, exhibit largely synchronous dynamics with O. brumata dominating at termination of the cyclic outbreaks (Tenow et al , 2007; Klemola et al , 2009). During 2002–2008, an outbreak of unprecedented extent and duration has swept through the mountain birch forest belt of northern Fennoscandia, affecting an estimated 10 000 km 2 or one‐third of the forested area (Jepsen et al , 2009a).…”

Section: Methodsmentioning

confidence: 99%

Rapid northwards expansion of a forest insect pest attributed to spring phenology matching with sub-Arctic birch

Jepsen

Kapari

Hagen

et al. 2010

Global Change Biology

134

117

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Species range displacements owing to shifts in temporal associations between trophic levels are expected consequences of climate warming. Climate-induced range expansions have been shown for two irruptive forest defoliators, the geometrids Operophtera brumata and Epirrita autumnata, causing more extensive forest damage in sub-Arctic Fennoscandia. Here, we document a rapid northwards expansion of a novel irruptive geometrid, Agriopis aurantiaria, into the same region, with the aim of providing insights into mechanisms underlying the recent geometrid range expansions and subsequent forest damage. Based on regional scale data on occurrences and a quantitative monitoring of population densities along the invasion front, we show that, since the first records of larval specimens in the region in 1997-1998, the species has spread northwards to approximately 701N, and caused severe defoliation locally during [2004][2005][2006]. Through targeted studies of larval phenology of A. aurantiaria and O. brumata, as well as spring phenology of birch, along meso-scale climatic gradients, we show that A. aurantiaria displays a similar dynamics and development as O. brumata, albeit with a consistent phenological lag of 0.75-1 instar. Experiments of the temperature requirements for egg hatching and for budburst in birch showed that this phenological lag is caused by delayed egg hatching in A. aurantiaria relative to O. brumata. A. aurantiaria had a higher development threshold (LDT A.a. 5 4.71 1C, LDT O.b. 5 1.41 1C), and hatched later and in less synchrony with budburst than O. brumata at the lower end of the studied temperature range. We can conclude that recent warmer springs have provided phenological match between A. aurantiaria and sub-Arctic birch which may intensify the cumulative impact of geometrid outbreaks on this forest ecosystem. Higher spring temperatures will increase spring phenological synchrony between A. aurantiaria and its host, which suggests that a further expansion of the outbreak range of A. aurantiaria can be expected.

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“…All the larvae collected were reared in the laboratory until they pupated, died, or parasitoid larvae emerged. Parasitism data from two other studies conducted in the same study area (2005)(2006)(2007) were used to increase the sample size in this observational data set (see Klemola et al 2008aKlemola et al , 2009). …”

Section: Moth Abundance and Parasitism Ratesmentioning

confidence: 99%

Experimental test of parasitism hypothesis for population cycles of a forest lepidopteran

Klemola

Andersson

Ruohomäki

et al. 2010

Ecology

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Abstract. Population cycles of herbivores are thought to be driven by trophic interaction mechanisms, either between food plant and herbivore or between the herbivorous prey and its natural enemies. Observational data have indicated that hymenopteran parasitoids cause delayed density-dependent mortality in cyclic autumnal moth (Epirrita autumnata) populations. We experimentally tested the parasitism hypothesis of moth population cycles by establishing a four-year parasitoid-exclusion experiment, with parasitoid-proof exclosures, parasitoid-permeable exclosures, and control plots. The exclusion of parasitoids led to high autumnal moth abundances, while the declining abundance in both the parasitoid-permeable exclosures and the control plots paralleled the naturally declining density in the study area and could be explained by high rates of parasitism. Our results provide firm experimental support for the hypothesis that hymenopteran parasitoids have a causal relationship with the delayed density-dependent component required in the generation of autumnal moth population cycles.

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Reversed Impacts by Specialist Parasitoids and Generalist Predators May Explain a Phase Lag in Moth Cycles: A Novel Hypothesis and Preliminary Field Tests

Cited by 25 publications

References 52 publications

Are population outbreaks in sub‐arctic geometrids terminated by larval parasitoids?

Are population outbreaks in sub‐arctic geometrids terminated by larval parasitoids?

Rapid northwards expansion of a forest insect pest attributed to spring phenology matching with sub-Arctic birch

Experimental test of parasitism hypothesis for population cycles of a forest lepidopteran

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