A response to Jepsen et al. (2016).

Important findings, e.g. in ecology, should be questioned and debated. Our findings that defoliating looper outbreaks travel as waves across Europe and the response here to such a questioning could be a start of a debate (photo: winter moth carterpillar).

Discovery of continental-scale travelling waves and lagged synchrony in geometrid moth outbreaks prompt a re-evaluation of mountain birch/geometrid studies.

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.

Geometrid outbreak waves travel across Europe.

We show that the population ecology of the 9- to 10-year cyclic, broadleaf-defoliating winter moth (Operophtera brumata) and other early-season geometrids cannot be fully understood on a local scale unless population behaviour is known on a European scale. Qualitative and quantitative data on O. brumata outbreaks were obtained from published sources and previously unpublished material provided by authors of this article. Data cover six decades from the 1950s to the first decade of twenty-first century and most European countries, giving new information fundamental for the understanding of the population ecology of O. brumata. Analyses on epicentral, regional and continental scales show that in each decade, a wave of O. brumata outbreaks travelled across Europe. On average, the waves moved unidirectionally ESE-WNW, that is, toward the Scandes and the Atlantic. When one wave reached the Atlantic coast after 9-10 years, the next one started in East Europe to travel the same c. 3000 km distance. The average wave speed and wavelength was 330 km year(-1) and 3135 km, respectively, the high speed being incongruous with sedentary geometrid populations. A mapping of the wave of the 1990s revealed that this wave travelled in a straight E-W direction. It therefore passed the Scandes diagonally first in the north on its way westward. Within the frame of the Scandes, this caused the illusion that the wave moved N-S. In analogy, outbreaks described previously as moving S-N or occurring contemporaneously along the Scandes were probably the result of continental-scale waves meeting the Scandes obliquely from the south or in parallel. In the steppe zone of eastern-most and south-east Europe, outbreaks of the winter moth did not participate in the waves. Here, broadleaved stands are small and widely separated. This makes the zone hostile to short-distance dispersal between O. brumata subpopulations and prevents synchronization within meta-populations. We hypothesize that hostile boundary models, involving reciprocal host-herbivore-enemy reactions at the transition between the steppe and the broadleaved forest zones, offer the best explanation to the origin of outbreak waves. These results have theoretical and practical implications and indicate that multidisciplinary, continentally coordinated studies are essential for an understanding of the spatio-temporal behaviour of cyclic animal populations.

On the consumption rate of Neodiprion sertifer - A reply to a comment by F. Slansky Jr.

As an answer to a comment by Slansky (Oecologia (Berl) 46 (1980) 133-134) on a recent statement by the present authors (Oecologia (Berl) 43 (1979) 157-172), it is maintained that an evaluation of the relative consumption rate (RCR) of N. sertifer must be made in relation to other tree-feeding herbivores, not to herb-feeders. The average value of available RCR estimates for tree-feeders is 1.3 mg/mg/day compared to 1.9 mg/mg/day for N. sertifer. Thus, we still maintain that N. sertifer has a high consumption rate.

Utilization of dry matter and bioelements in larvae of Neodiprion sertifer Geoffr. (Hym., Diprionidae) feeding on Scots pine (Pinus sylvestris L.).

In the laboratory the consumption (C), egestion (F), assimilation (A) and assimilation efficiency (A/C) of dry matter and of the bioelements C, N, P, K, Ca, Mg, S and Na were studied weekly during the whole feeding stage. The larvae were reared in clusters of 10 individuals (on average 3.5 ♂♂ and 6.5 ♀♀), fed one-year-old needles. The average values of (C), (F) and (A) were 2,950, 2,530 and 414 mg dw per cluster, respectively, implying a dry matter assimilation efficiency of only 14.0%. The mean production of tissue (P) per cluster amounted to 250 mg dw. The concentration of bioelements in faeces (in order as above) was 51.2, 0.80, 0.08, 0.36, 0.41, 0.11, 0.10 and 0.02% of dw, and in larval tissue 57.5, 7.60, 0.64, 0.85, 0.24, 0.22, 0.24 and 0.06% of dw, respectively. The concentration of N and P in larval tissue was 5.8 and 4.9 times higher than in food, that of K, Mg, S and Na about twice, that of C and Ca about equal or less. The assimilation efficiency of the bioelements was estimated at 14.5, 59.3, 47.4, 20.9, 4.6, 12.5, 13.8 and 44.4%, and the energetics (C), (F), (A), (P) and (R=A-P) at 61,900, 53,600, 8,320, 6,710 and 1,610 J per cluster, respectively. It is argued that in N. sertifer the high consumption rate, low efficiency of dry matter assimilation and low nitrogen accumulation, in all attained at a low maintenance cost, are adaptations to a food low in nitrogen content (1.3% of dw). The study is part of an investigation on the interaction between insect consumption and pine growth, performed within the Swedish Coniferous Forest Project.