Abstract
The spatio-temporal dynamics of populations of two 9-10 year cyclic-outbreaking geometrids, Operophtera brumata and Epirrita autumnata in mountain birch forests in northern Fennoscandia, have been studied since the 1970´s by a Swedish-Norwegian research team and, during the last decade, by Norwegian and Finnish research teams. Some of the early results have been challenged by the Norwegian team. To examine the base for disagreements, five of the papers published by the Norwegian team (2004-2011) are reviewed. It is found that conclusions in these papers are questionable or data could not be interpreted fully because two decisive traits in the spatio-temporal behaviour of outbreaks of the two species were not considered.
Highlights
Two recent observations of the spatio-temporal outbreak pattern of some extensively studied geometrid moth species necessitate a re-evaluation of previously published findings
It has been demonstrated that defoliating outbreaks on deciduous trees of the winter moth (Operophtera brumata L.) and associated geometrids every 9–10 years travel as a wave across Europe from east to west with the front of the wave stretching from high to low latitudes1
Long-term studies on the temporal behaviour of Epirrita autumnata, an associated geometrid, and O. brumata in the mountain chain of Scandinavia and northern Finland show that outbreaks of O. brumata have been synchronized with those of E. autumnata with a time lag of about 1–2 years2–4
Summary
Two recent observations of the spatio-temporal outbreak pattern of some extensively studied geometrid moth species necessitate a re-evaluation of previously published findings. To be comparable, the analysis for the two geometrids should probably have covered the same phases of the outbreak cycle (increase, peak, crash), or the years 2002–2004 (2005) for E. autumnata and, with the time lag, the years 2003–2005 (2006) for O. brumata It is stated that “Where the two species occur sympatrically within their outbreak range, there is a partial interspecific synchrony in the timing of the outbreaks, but with winter moth often lagging 1–2 years behind autumnal moth....” If this well-known 1–2 year lag (e.g. Hagen 200717; Tenow et al 20073; Klemola et al 20084) is applied to the satellite mapping (in addition to the acceptance of waves), it is evident that there was a lagged defoliation pattern in this case, i.e., defoliations by E. autumnata in 2002–2003 at Varangerfjord and by O. brumata in 2005–2007 in the same area. Grant information The author(s) declared that no grants were involved in supporting this work
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