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Monitoring outbreaks of the autumnal and winter moth in Fennoscandia: moth occurrence and history over > 100 years

by Olle Tenow, Arne C. Nilssen and Helena Bylund (2007)

The outbreaking geometrids the autumnal moth (Epirrita autumnata) and the winter moth (Operophtera brumata) occur circumpolar where they defoliate an array of different host trees, in northern Fennoscandia mainly birch (Betula spp.). In southern Fennoscandia and on the European continent, O. brumata preferably attacks fruit trees and oak, and its close relative, the large winter Moth (O. fagata), mainly beech (Fagus silvatica) and birch. Other associate geometrids to the south are the scarce umber (Agriopis aurantiaria) and the mottled umber (Erannis defoliaria). The life cycles of all these geometrids are similar. Fig1. Click for larger image

Fig. 1. A) Operophtera brumata and O. fagata. B) Epirrita autumnata, C) Agriopis aurantiaria and D) Erannis defoliaria


In Iceland, only O. brumata occurs and in the 1930´s it was accidentally introduced to North America. In North America, E. autumnata is known to defoliate conifer trees. A native counterpart to O. brumata is the Bruce Spanworm (O. bruceata) which mainly attacks aspen trees. This species also occurs in Greenland where it is a severe defoliator of birch forests. E. autumnata is indigenous in Fennoscandia and may have followed the immigration of birch after the retreat of the inland ice and outbreaks may be of ancient age. Far before the reporting of O. brumata occurrence or of its outbreaks in Fennoscandia, it is thought, the species was introduced with fodder to Iceland and the Faeroes by seafaring Norsemen, in due course resulting in outbreaks on the Icelandic birch forests. Similarly, Norse settlers in North America probably introduced O. bruceata to Greenland (e.g. Downes 1988).

The first written witness ever of an outbreak is from 1762. Hermann Ruge, a parish priest in central South Norway then wrote that in Nord Valdres larvae of Phalenarum and Pappilionum, i.e. moths and butterflies, only a few years earlier devastated the birch forest on the mountain slopes that the forest could neither have any value, nor be restored. His remark indicates that several moth species participated in the outbreak.Fig2. Click for larger image





Fig. 2. The Ruge report.


In the later half of the 19th century, forests began to be economically valuable and gradually networks of larger and smaller forestry management districts were laid out over our countries, each under charge of a forest officer, who, among other thFig3. Click for larger imageings, had to keep an eye on harmful insects. In addition, positions as state entomologists were created. Norway was first out when Wilhelm Maribo Schøyen was appointed in 1894, followed by Sven Lampa 1897 in Sweden and Enzio Reuter 1901 in Finland. Thanks to these foresters and entomologists who reported and published annually about outbreaks, also on fruit trees, the moth outbreaks can be followed almost 150 years back in time. Schøyen and J. Sparre Schneider, first to be appointed Curator at Tromsø Museum, were personally interested in the outbreaks of E. autumnata and O. brumata. Sparre Schneider recorded in 1901 on the first finds (in 1878 and 1892) and the first outbreak (in 1897-1900 on Tromsøen) of O. brumata in Troms County which could be interpreted as the spread of O. brumata outbreaks in North Norway into new areas. Already in 1878, Schöyen as the first one to notice that E. autumnata is an outbreak species, published a summary on local outbreaks in Norway which he followed up in 1891. Also in 1891, Axel Hagemann, a forest officer in Vest-Finnmark concluded that the outbreaks were periodic. Other historical judgements were: “marked periodic mass-occurrences” by Ivar Trägårdh in 1921 and “large outbreaks with 10-year intervals in Troms” by Thor Hiort Schøyen in 1949.

Fig. 3. W.M. Schøyen (top) and J. Sparre Schneider


Table 1 . The 130 year history of outbreak monitoring.


W.M. Schøyen points out the E. autumnata as an important outbreak species.


W.M. Schøyen lists outbreak localities and years that cover four early outbreak


A. Hagemann notes that mass-occurrences of E. autumnata are periodic.


J. Sparre Schneider documents what is probably the first outbreak of O. brumata on birch in Troms County.


I. Trägårdh describes E. autumnata outbreaks as being marked periodic.


T.H. Schøyen observes that severe outbreaks have occurred with an interval of 10 years in Troms County.


O. Tenow compiles all known reports on outbreaks, describes 12 separate outbreak periods from 1862 to 1968, finds that periods occur with an average interval of 9-10 years, that outbreaks of E. autumnata and O. brumata are synchronized, and that the outbreaks during several periods have moved like a wave from north to south.


S. Neuvonen shows that E. autumnata outbreaks north of Lat. 65 N° have been truly cyclic.


H. Tömmervik et al. use remote sensing to detect outbreaks.


R.A. Ims et al. challenge the idea that northern O. brumata populations exhibit large scale spatial synchronous dynamics.


T. Klemola et al. show that outbreaks of E. autumnata during the most recent four outbreak periods have on average moved as “travelling waves” from ENE to WSW over northern Fennoscandia.


O. Tenow et al. demonstrate that the E. autumnata and O. brumata outbreaks during the 1990´s “moved” like a wave from E to W in northern Fennoscandia and that O. brumata lagged 1-2 years after E. autumnata.


A.C. Nilssen et al. up-date the 1972 outbreak survey by adding three more outbreak periods (in the 1970´s, 1980´s and 1990´s).


S.B. Hagen et al. and J.U. Jepsen et al. find that the outbreaks of E. autumnata and O. brumata have expanded into new areas in North Norway as a consequence of a warmer climate.


The first international workshop on monitoring E. autumnata and O. brumata outbreaks is launched in 14-17 August at Svanhovd, Kirkenes Commune.


In 1972, Olle Tenow demonstrated that there have been twelve outbreak periods from 1862 to 1968 with a mean interval of 9-10 years and that several outbreak periods had started in the north and then moved southward like a wave. In 1988, Seppo Neuvonen could show that E. autumnata outbreaks north of Lat 65° N have been truly cyclic. However, a deviating view of the fluctuations was given in 2004 by Ims et al. In a monitoring study they found that the O. brumata populations on nearby coast islands of north-western Norway did not fluctuate in synchrony and therefore questioned in general the existence of large-scale spatially synchronized fluctuations.

In recent years, the study of synchronization of outbreaks has focused on “travelling waves”, i.e. the directed move of local outbreaks during an outbreak period. In E. autumnata outbreaks, such moves were reported in 2006 by Tero Klemola et al. to occur from ENE to WSW over northern Fennoscandia. They concluded that autumnal moth populations are indeed synchronous at large spatial scales. Since 1972, four more outbreak periods (in the 1970´s, 1980´s, 1990´s and 2000´s) have been recorded by Klemola et al. in 2006 and by Arne C. Nilssen et al. in 2007. It was also shown that outbreaks sometimes move from E to W over northern Fennoscandia and that the outbreaks of O. brumata were synchronized with those of E. autumnata with a lag of a couple of years (Tenow et al. 2007).

High latitude and high altitude ecosystems in particular are assumed to be sensitive to global warming and therefore suitable for monitoring early changes as responses to warming. In 2007, Snorre B. Hagen et al. and Jane Uhd Jepsen et al. (submitted) could demonstrate that the outbreaks of E. autumnata and O. brumata have spread vertically and horizontally into new areas in northern Fennoscandia as a consequence of a warmer climate. In addition, A. aurantiaria has for the first time established as an outbreak species in Troms County, north-western Norway (A.C. Nilssen, unpubl. data). A. aurantiaria is previously known to attack birch forest together with E. autumnata and O. brumata only in southern Norway.

During recent outbreak periods, monitoring of outbreaks has been done by aircraft and satellite surveillance (Tømmervik et al. 2001), however with difficulties to define what defoliation level should represent an outbreak. This may be problematic even as “truth on the ground”, evaluated either by estimating the loss of foliage or by estimating defoliator numbers.

Finally, an important step was taken with the invitation to the first international workshop for “developing a concerted protocol for targeted hypothesis-based monitoring in Fennoscandia and Kola Peninsula” at Svanhovd, Kirkenes Commune, on 14-17 August 2007, initiated by Rolf A. Ims and colleagues at Tromsø University.