Ecological Entomology (2012) 37, 471-479

Tino Schott, Rolf A. Ims, Snorre B. Hagen and Nigel G. Yoccoz (2012)
Sources of variation in larval parasitism of two sympatrically outbreaking birch forest defoliators
Ecological Entomology 37 (6), 471-479
Abstract: 1. Studies of insect communities rarely support the parasitoid-host regulation hypothesis. Spatio-temporal variation in parasitoid prevalence due to complex food web interactions or abiotic factors may prevent parasitoids from regulating hosts.
2. We examined the relative contribution of spatial (altitude) and temporal (years) sources to total variation in parasitoid prevalence rates in outbreaks of Epirrita autumnata Borkhausen and Operophtera brumata Linnaeus populations. We tested whether prevalence rates of generalist parasitoids were correlated between sympatric host populations and to what extent any of the parasitoids were host density dependent.
3. Four larval parasitoids (two specialists and two generalists) exhibited significantly structured spatio-temporal dynamics over years and altitudes. The prevalence rates of one of the generalists were spatio-temporally correlated between the two host species, while for the other they were not.
4. Three parasitoids showed tendencies for direct or delayed positive density dependence as expected from numerical and functional responses to their hosts. However, the effects were weak and minute compared to the variation attributed to year and altitude.
5. We conclude that unknown aspects of the larval parasitoid ecology that co-vary with altitude and year in the study system dominate their prevalence dynamics and thus act to hinder density-dependent responses that could potentially regulate host populations.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Link to article at publishers website
Database assignments for author(s): Tino Schott

Research topic(s) for pests/diseases/weeds:
biocontrol - natural enemies
Research topic(s) for beneficials or antagonists:
environment/habitat manipulation
surveys/distribution/isolation

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Operophtera brumata	Birch (Betula)	Norway
	Epirrita autumnata	Birch (Betula)	Norway