Creating multiyear cycles in population density demands, in traditional models, causal factors that operate on local populations in a density-dependent way with time lags. However, cycles of the geometrid Epirrita autumnata in northern Europe may be regional, not local; i.e., successive outbreaks occur in different localities. We review possible causes of cycles of E. autumnata under both local and regional scenarios, including large-scale synchrony. Assuming cyclicity is a local phenomenon, individual populations of E. autumnata display peaks but populations all over the outbreak range fluctuate in synchrony. This concept assumes that the peaks at most localities are so low that they do not lead to visible defoliation and easily remain unnoticed. In this scenario, populations are able to start recovery a few years after the crash, i.e., at the time of the mitigation of detrimental delayed density-dependent factors, such as delayed inducible resistance of the host plant or parasitism. In that case, the same factors that lead to crashes also explain the periodicity of cyclic fluctuations. According to the regional cyclicity scenario, different factors can be important in different phases of the cycle. The key is to identify the factors that tend to produce outbreaks with a periodicity of about 10 years. Initiation of the increase phase seems to coincide with maxima in sunspot activity, but causal connections remain unclear. Climatic factor(s) associated with the solar cycle could contribute to the large-scale geographic synchrony.

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Plant monocultures are commonly believed to be more susceptible to herbivore attacks than stands composed of several plant species. However, few studies have experimentally tested the effects of tree species diversity on herbivory. In this paper, we present a meta-analysis of uniformly collected data on insect herbivore abundance and damage on three tree species (silver birch, black alder and sessile oak) from seven long-term forest diversity experiments in boreal and temperate forest zones. Our aim was to compare the effects of forest diversity on herbivores belonging to different feeding guilds and inhabiting different tree species. At the same time we also examined the variation in herbivore responses due to tree age and sampling period within the season, the effects of experimental design (plot size and planting density) and the stability of herbivore responses over time. Herbivore responses varied significantly both among insect feeding guilds and among host tree species. Among insect feeding guilds, only leaf miner densities were consistently lower and less variable in mixed stands as compared to tree monocultures regardless of the host tree species. The responses of other herbivores to forest diversity depended largely on host tree species. Insect herbivory on birch was significantly lower in mixtures than in birch monocultures, whereas insect herbivory on oak and alder was higher in mixtures than in oak and alder monocultures. The effects of tree species diversity were also more pronounced in older trees, in the earlier part of the season, at larger plots and at lower planting density. Overall our results demonstrate that forest diversity does not generally and uniformly reduce insect herbivory and suggest instead that insect herbivore responses to forest diversity are highly variable and strongly dependent on the host tree species and other stand characteristics as well as on the type of the herbivore.

Within Fennoscandia, two well‐studied groups of herbivores exhibit clear geographical gradients in their population dynamics. Populations of a forest lepidopteran (Epirrita autumnata, the autumnal moth) and voles of the genera Microtus and Clethrionomys show pronounced multi‐annual cycles in the north but become more stable towards the south. Here we review empirical and theoretical studies on these species, mainly regarding the biological mechanisms that are assumed to generate the pattern of population dynamics in both systems. We conclude that the specialist/generalist predation hypothesis offers a common explanation for the population cycles and their geographical gradients irrespective of whether a herbivorous insect or small mammals are concerned. According to this hypothesis, originally developed for the Fennoscandian voles, but now applied also to E. autumnata, population cycles are generated by specialist natural enemies (predators for the voles and parasitoids for E. autumnata). Furthermore, the dynamic shift from cycles to stability is assumed to be caused by an increase in the density and diversity of generalist natural enemies from north to south in Fennoscandia.

A national crowdsourcing-based tick collection campaign was organized in 2015 with the objective of producing novel data on tick distribution and tick-borne pathogens in Finland. Nearly 20 000 Ixodes ticks were collected. The collected material revealed the nationwide distribution of I. persulcatus for the first time and a shift northwards in the distribution of I. ricinus in Finland. A subset of 2038 tick samples containing both species was screened for Borrelia burgdorferi sensu lato (the prevalence was 14.2% for I. ricinus and 19.8% for I. persulcatus), B. miyamotoi (0.2% and 0.4%, respectively) and tick-borne encephalitis virus (TBEV; 0.2% and 3.0%, respectively). We also report new risk areas for TBEV in Finland and, for the first time, the presence of B. miyamotoi in ticks from mainland Finland. Most importantly, our study demonstrates the overwhelming power of citizen science in accomplishing a collection effort that would have been impossible with the scientific community alone.