title: Can sunspot activity and ultraviolet-B radiation explain cyclic outbreaks of forest moth pest species?
abstract: 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.
authors.affiliation: Department of Ecology, Agricultural University of Norway, PO Box 5003, NO-1432 As. vidar.selas@ina.nlh.no
authors.forename: Vidar
authors.initials: V
authors.lastname: Selås
authors.forename: Olav
authors.initials: O
authors.lastname: Hogstad
authors.forename: Sverre
authors.initials: S
authors.lastname: Kobro
authors.forename: Trond
authors.initials: T
authors.lastname: Rafoss
mesh_terms: D000818:Animals; D001272:Atmosphere / Q000737:chemistry; D009036:Moths / Q000254:growth & development / Q000502:physiology*; D009664:Norway; D010126:Ozone; D011156:Population Density; D011157:Population Dynamics; D012044:Regression Analysis; D012621:Seasons; D019445:Solar Activity; D014197:Trees; D014466:Ultraviolet Rays
chemical_list: D010126:Ozone