Can sunspot activity and ultraviolet-B radiation explain cyclic outbreaks of forest moth pest species?

Cyclic outbreaks of forest moth pest species have long remained a puzzle for foresters and ecologists. This paper presents time-series exhibiting a strong negative relationship between sunspot numbers and population indices of autumnal and winter moths, both in a mountain birch forest in central Nor...

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Bibliographic Details
Published in:Proceedings of the Royal Society. B, Biological sciences Biological sciences, 2004-09, Vol.271 (1551), p.1897-1901
Main Authors: Selas, V, Hogstad, O, Kobro, S, Rafoss, T
Format: Article
Language:English
Subjects:
Animals
Atmosphere - chemistry
Forest ecology
Hardwood trees
Herbivore Resistance
Herbivores
Lepidoptera
Lowland forests
Lowlands
Mixed forests
Moth Cycles
Moths
Moths - growth & development
Moths - physiology
Norway
Ozone
Pest Species
Population Density
Population Dynamics
Regression Analysis
Seasons
Solar Activity
Sunspots
Trees
Ultraviolet Rays
Ultraviolet-B
Winter
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Summary:Cyclic outbreaks of forest moth pest species have long remained a puzzle for foresters and ecologists. This paper presents time-series exhibiting a strong negative relationship between sunspot numbers and population indices of autumnal and winter moths, both in a mountain birch forest in central Norway and in a mixed lowland forest in southern Norway. In the latter area, also the population level of a moth species feeding entirely on lichens was negatively related to sunspot numbers. Low sunspot activity leads to a thinner ozone layer and thus higher surface ultraviolet (UV)-B radiation. As winter moth larvae prefer leaves subjected to enhanced UV-B radiation, we suggest that the causal relationship between sunspots and moths is that the metabolic costs of producing UV-B-protective pigments during periods of low sunspot activity reduce trees' and lichens' resistance to herbivores, and thus increase the survival of moth larvae. Higher peak densities of moth cycles in mountain forests could be explained by the general higher UV-B radiation at higher altitudes.
ISSN:0962-8452
1471-2954
DOI:10.1098/rspb.2004.2811