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Phenotypic plasticity and local adaptations are important factors in predicting range expansions and shifts of pest insects in a changing climate. We reared two lepidopteran forest pests, Lymantria monacha (Linnaeus) and Lymantria dispar (Linnaeus), at three climatically different field sites from central Germany to northern Finland to investigate differences among populations in plasticity in the timing of pupation and adult emergence (measured as cumulative temperature sums, degree-days >5 [degrees]C), pupal mass, and duration of the pupal period. We also compared the phenologies of continental and boreal L. monacha populations feeding on Scots pine (Pinus sylvestris L.) to reveal possible local adaptations. Lymantria dispar was reared on different host plants, Quercus robur L., Betula pendula Roth, and Betula pubescens ssp. czerepanovii (Orl.) Hamet-Ahti, to evaluate the possibilities of a range expansion northwards. There was stronger indication of adaptive phenotypic plasticity, which enables species to cope with changing environmental conditions, in continental L. dispar and boreal L. monacha populations than in the continental L. monacha population. Differences between boreal and continental L. monacha populations may denote adaptation to local conditions. All three host plants used for L. dispar proved suitable for the species, revealing that host plant availability would not limit its range expansion in northern Europe. Key words: climate change, local adaptation, Lymantria monacha, Lymantria dispar, phenotypic plasticity. La plasticite phenotypique et les adaptations locales sont des facteurs importants lorsqu'il s'agit de prevoir l'expansion et les modifications de l'aire de repartition des insectes ravageurs dans le contexte du changement climatique. Nous avons eleve deux ravageurs forestiers du groupe des lepidopteres, Lymantria monacha (Linnaeus) et Lymantria dispar (Linnaeus), a trois endroits sur le terrain differents du point de vue climatique, allant du centre de l'Allemagne au nord de la Finlande pour etudier les differences parmi les populations du point de vue de la plasticite dans le moment de la nymphose et de l'emergence des adultes (mesuree par la somme cumulative des temperatures, degres-jours >5 [degrees]C), la masse des nymphes et la duree de la periode nymphale. Nous avons aussi compare la phenologie des populations continentale et boreale de L. monacha qui s'attaquent au pin sylvestre (Pinus sylvestris L.) pour trouver d'eventuelles adaptations locales. Lymantria dispar a ete eleve sur differentes plantes hotes, Quercus robur L., Betula pendula Roth et Betula pubescens ssp. czerepanovii (Orl.) Hamet-Ahti, pour evaluer les possibilites d'expansion de son aire de repartition vers le nord. Les indices de plasticite phenotypique adaptative, qui permet aux especes de faire face aux changements des conditions environnementales, etaient plus significatifs chez les populations continentale de L. dispar et boreale de L. monacha que chez la population continentale de L. monacha. Les differences entre les populations boreale et continentale de L. monacha sont peut-etre un indice d'adaptation aux conditions locales. Les trois plantes hotes utilisees dans le cas de L. dispar se sont averees adequates pour cette espece, indiquant que la disponibilite de plantes hotes ne limiterait pas l'expansion de son aire de repartition dans le nord de l'Europe. [Traduit par la Redaction] Mots-cles : changement climatique, adaptation locale, Lymantria monacha, Lymantria dispar, plasticite phenotypique., Introduction The influence of climate change on butterflies and moths, especially charismatic, conspicuous species and those considered as forest or agricultural pests, has been investigated intensively in recent years (e.g., [...]

Population cycles of herbivores are thought to be driven by trophic interaction mechanisms, either between food plant and herbivore or between the herbivorous prey and its natural enemies. Observational data have indicated that hymenopteran parasitoids cause delayed density-dependent mortality in cyclic autumnal moth (Epirrita autumnata) populations. We experimentally tested the parasitism hypothesis of moth population cycles by establishing a four-year parasitoid-exclusion experiment, with parasitoid-proof exclosures, parasitoid-permeable exclosures, and control plots. The exclusion of parasitoids led to high autumnal moth abundances, while the declining abundance in both the parasitoid-permeable exclosures and the control plots paralleled the naturally declining density in the study area and could be explained by high rates of parasitism. Our results provide firm experimental support for the hypothesis that hymenopteran parasitoids have a causal relationship with the delayed density-dependent component required in the generation of autumnal moth population cycles. Key words: autumnal moth; delayed density dependence; Epirrita autumnata; Fennoscandia; forest Lepidoptera; herbivores; mountain birch; parasitoid exclusion experiment; parasiloids; population cycles; trophic interactions.

To purchase or authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.0030-1299.2008.15972.x Byline: Harri Vehvilainen, Julia Koricheva, Kai Ruohomaki Abstract: Diverse plant communities are predicted to have higher abundance of predators as compared to species-poor ones. In this study we explored whether this prediction holds true for the abundance of predatory arthropods in forest ecosystems, which have been poorly studied in this respect. We collected ground-dwelling arthropods using pitfall traps from six long-term forest diversity experiments in Finland, Sweden and UK. The effects of tree species diversity on abundance of five main groups of predatory arthropods (ants, spiders, carabids, staphylinids and opilionids) were examined by means of meta-analysis. Overall, the diversity of tree species did not affect abundances of predators with the exception of staphylinids, which were more abundant in mixed stands than in monocultures. However, the effects of stand diversity on predator abundance became apparent when analyses were conducted on tree species basis. Preference for stands containing particular tree species was clear in the case of opilionids, carabids and staphylinids, and these preferences overruled the effects of tree species diversity in comparisons between monocultures and mixed stands containing the same tree species. Tree species diversity effects on predator abundance were furthermore mediated by the tree age, plot size and planting density used in the experiment. Overall, our results show that predator abundance does not increase uniformly with increase in tree species diversity, but rather suggest that predators have distinct preferences for stands composed of particular tree species and that these species preferences may overrule the effects of diversity. Article History: Manuscript Accepted 11 February 2008 Article note: H. Vehvilainen, Biometrical Genetics, Biotechnology and Food Research, MTT Agrifood Research Finland, FI-31600 Jokioinen, Finland. - J. Koricheva (julia.koricheva@rhul.ac.uk), School of Biological Sciences, Royal Holloway Univ. of London, Egham, Surrey, UK, TW20 0EX. - K. Ruohomaki, Dept of Biology, Univ. of Turku, FI-20014 Turku, Finland.

Abstract: Pure forest stands are widely believed to be more prone to pest outbreaks and disease epidemics than mixed stands, leading to recommendations of using stand diversification as a means [...]

Research shows that animal population cycles are produced by specialist natural enemies, such as preditors and parasitoids, while population stability is generated by diversity and density of generalist natural enemies. Studies were conducted on vole and moth communities in Scandinavia.

Research on the effects of Epirrita autumnata caterpillar larvae on Betula pubescens mountain birch is presented, contrasting laboratory and caged tests with uncaged tests. The disappearance rate of uncaged larvae was correlated with young age of stems and previous defoliation. In general, isappearance rate changes were larger than consumption and growth rate changes.

Most damage caused by invertebrate herbivores is local and limited in extent and may therefore seem inconsequential. However, in addition to providing photosynthates to the whole plant, individual leaves may preferentially feed local sinks, including primordial meristems that develop later. For leaf damage, this may have local consequences and, in the case of preformed meristems, may result in time lags. To investigate such consequences and to determine the degree of independence among shoot modules, we studied shoot traits after damage to individual leaves in long shoots and vegetative and generative short shoots of field-growing mountain birch, Betula pubescens subsp. czerepanovii (Orlova) Hamet-Ahti. For short shoots, the results suggest that, due to the catkin, generative shoots have a higher priority in resource use than vegetative shoots. The overwinter survival of vegetative short shoots was decreased after their young leaves had been damaged early in the previous season. Otherwise, there were no significant effects of leaf damage on vegetative shoots. In generative shoots, leaf damage affected size and reproduction instead of survival. Because leaf damage significantly decreased leaf size in the generative shoots in the posttreatment year, leaves presumably competed with the catkin for resources within the shoot. Damage also reduced the catkin mass and the mean seed mass in the treatment year. In the posttreatment year, catkin mass and total seed mass were reduced by the treatments, but differences in the number of seeds and mean seed mass did not quite reach significance. The treatments had no effects on leaf mass of neighbors of vegetative or generative shoots in the treatment year or in the posttreatment year. In the treatment year, removal of long shoot leaves from a growing long shoot did not affect growth of the long shoot, indicating that such growth was supported by resources external to the shoot. However, local effects were evident in the posttreatment year: leaf mass decreased in shoots that developed from axillary buds in long shoots whose supporting leaves had been clipped in the previous year. Consequently, removal of individual leaves may have local effects on shoot survivorship, reproduction, and growth. Timing of damage and shoot type modified the consequences of local leaf damage, and there were no consistent responses for all situations. Due to the limited extent of damage, the effects were not likely to result from nutrient loss due to damage. Instead, consequences of local leaf damage could be explained largely by effects on local sinks and meristem primordia. Key words: carbon; compensatory ability; generative and vegetative shoots; independence of modules; leaf value; local leaf damage; modularity; mountain birch; northern Finland; simulated herbivory; source-sink hypothesis., INTRODUCTION Trees are typically modular in structure, i.e., they are constructed of repetitive, multicellular units (Vuorisalo and Tuomi 1986). These units have been assumed to be semi-independent, especially in their [...]

Various experimental trees are subjected to long-lasting defoliation by uncaged insect larvae study the herbivore-elicited changes in the growth of the branching hierarchy within the crowns of mountain birch at all the levels. The results show that the source-sink interactions highly affect the control of resource allocation within a larger scale, as a plant's responses to localized herbivory involves both localized, as well as integrated components.

Patterns of spatial synchrony among cyclic autumnal moth Epirrita autumnata populations across Fennoscandina are described. A positive correlation in population growth rates between the time series was observed indicating spatial synchrony and results emphasized that high amounts of environmental variation may result in a clear structuring of spatial synchrony at unexpectedly small scales.

In the case of an insect larvae always maximizing its weight gain. Results of the test conducted to determine the growth rate maximiser status of the geometrid moth Epirrita autumnata are presented.

The specific nature of crowding effects of Epirrita autumnata in the field is investigated. The magnitude, density threshold and adaptiveness of the responses for crowded larvae are examined.

The effects of predation and oviposition activity on reproductive success of a late-season moth, Epirrita autumnata, are investigated. The reproductive success of non-outbreaking Epirrita autumnata is decreased by 60-85 percent and egg mortality is decreased by 20-40 percent due to adult predation.

We conducted a two-year predator-exclusion study to assess the magnitude and timing of larval predation in non-outbreaking populations of a geometrid moth, Epirrita autumnata. Laboratory-produced newly hatched larvae were placed on the experimental trees which were assigned to five treatments within two larval densities: (1) all predators, including parasitoids, excluded by mesh bag, (2) birds excluded by cage, (3) ants excluded by glue ring, (4) birds and ants excluded, and (5) control without any predator exclusion. Thereafter, larvae were censused every 3-4 d throughout the five-instar larval period. Mortality of E. autumnata larvae in these populations was high and mostly due to natural enemies. In control trees, only ~10% of larvae survived, while survival was ~90% in mesh bags preventing all natural enemies. Bird exclusion significantly improved larval survival, as survival was almost three times higher in trees with cages than in those without cages. On the other hand, ant exclusion did not have any overall effects on larval survival, mostly because ants were only detected in about half of the trees without glue rings. Larvae survived longer in high-density trees from which ants were excluded, but the effect was masked by high mortality, unrelated to ant exclusion, in the late larval season. The results suggest that the effect of ant predation on survival of E. autumnata larvae may be spatially restricted and not important at a larger scale. The same result applies for crab spiders, as they caused high mortality in ~20% of the study trees. Our results emphasize the importance of considering the spatial scale as well as assessing the impact of multiple predators in order to detect predators affecting survival at the population level. Exclusion of all predation had a significantly stronger effect on larval survival than exclusion of birds alone. Further, mortality was highest during the late larval period, when parasitoids emerge. Thus, a large proportion of larval mortality was most likely due to parasitism. Our results suggest that predation by passerine birds and parasitism may contribute to maintenance of low E. autumnata densities by strong suppression of the number of larvae entering the pupal stage. Key words: ants; birds; crab spiders; Epirrita autumnata; field experiment; insect herbivore; larval predation; parasitism; predator exclusion; stability; suppression; survival analysis.

Pupal period is highly variable in Epirrita autumnata (Lepidoptera, Geometridae) lasting from about one to over three months. We aimed to find proximate and ultimate explanations for the high variability, including the possibility that variation in eclosion time represents a diversified bet-hedging strategy. Patterns of variation in pupal period, both among and within populations, were analyzed in several common environment experiments, including one with a half-sib design. We further assessed possible selective forces on eclosion date and its variance using an empirical simulation model. Latitudinal among-population differences in pupal period were shown to have a genetic basis. Within populations, there was a considerable among-sibship variance in this trait that suggests high heritabilities of pupal period. The environmental component of the variance was unlikely to result from a deterministic reaction norm, neither adaptive nor constraint-based, and may thus represent a type of variance on which a bet-hedging strategy can be based. Importantly, there were significant among-sibship differences in the variance itself, and a significant sire effect on offspring variability in the half-sib design. This suggests a possibility for the variance in pupal period to be selected for as such, and for increased random environmental variance (a bet-hedging strategy) to evolve via natural selection. We assumed that seasonal changes in night temperatures and predation rate determine the optimal timing of adult flight period in E. autumnata. Results of modeling suggested that there are apparently flat fitness profiles in relation to eclosion date, which is the probable reason for maintenance of high genetic diversity in pupal period. Unpredictable temperature during adult flight period has a potential to select for high variance in eclosion dates, although the selective pressure appears to be weak. Genetic variance in variance of pupal period may thus be largely selectively neutral in the studied system. Key words: adaptation; bet-hedging; emergence distribution; empirical modeling; environmental variance; Epirrita autumnata; Geometridae; half-sib design; heritability; Lepidoptera; pupal period., INTRODUCTION Maintenance of phenotypic variance in natural populations continues to be an area of major interest in evolutionary biology. Phenology-related traits of annual life cycles, in insects in particular, are [...]

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 canbe 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 withmaxima in sunspot activity, but causal connections remain unclear. Climatic factor(s) associated with the solar cycle could contribute tothe large-scale geographic synchrony. [ABSTRACT FROM AUTHOR]