Expansion of the winter moth outbreak range : no restrictive effects of competition with the resident autumnal moth

1. Both direct and indirect competition can have profound effects on species abundance and expansion rates, especially for a species trying to strengthen a foothold in new areas, such as the winter moth (Operophtera brumata) currently in northernmost Finland. There, winter moths have overlapping outbreak ranges with autumnal moths (Epirrita autumnata), who also share the same host, the mountain birch (Betula pubescens ssp. czerepanovii). Competitive interactions are also possible, but so far unstudied, are explanations for the observed 1–3 years phase lag between the population cycles of the two moth species. 2. In two field experiments, we studied host plant-mediated indirect inter-specific competition and direct interference/exploitation competition between autumnal and winter moths. The experimental larvae were grown either with the competing species or with the same number of conspecifics until pupation. Inter-specific competition was judged from differences in pupal mass (reflecting lifespan fecundity), larval development time and larval survival. 3. Larval performance measurements suggested that neither direct nor indirect interspecific competition with the autumnal moth reduce the growth rate of winter moth populations. Winter moths even had a higher probability of survival when reared together with autumnal moths. 4. Thus, we conclude that neither direct nor indirect inter-specific competition is capable of suppressing the spread of the winter moth outbreak range and that both are also an unlikely cause for the phase lag between the phase-locked population cycles of the two moth species

Larval parasitism of the autumnal moth reduces feeding intensity on the mountain birch

Plants respond to grazing by herbivorous insects by emitting a range of volatile organic compounds, which attract parasitoids to their insect hosts. However, a positive outcome for the host plant is a necessary precondition for making the attraction beneficial or even adaptive. Parasitoids benefit plants by killing herbivorous insects, thus reducing future herbivore pressure, but also by curtailing the feeding intensity of the still living, parasitised host. In this study, the effect of parasitism on food consumption of the 5th instar larvae of the autumnal moth (Epirrita autumnata) was examined under laboratory conditions. Daily food consumption, as well as the duration of the 5th instar, was measured for both parasitised and non-parasitised larvae. The results showed that parasitism by the solitary endoparasitoid Zele deceptor not only reduced leaf consumption significantly but also hastened the onset of pupation in autumnal moth larvae. On the basis of the results, an empirical model was derived to assess the affects on the scale of the whole tree. The model suggests that parasitoids might protect the tree from total defoliation at least at intermediate larval densities. Consequently, a potential for plant–parasitoid chemical signalling appears to exist, which seems to benefit the mountain birch (Betula pubescens ssp. czerepanovii) by reducing the overall intensity of herbivore defoliation due to parasitism by this hymenopteran parasitoid

Responses of generalist invertebrate predators to pupal densities of autumnal and winter moths under field conditions

1. Generalist natural enemies are usually not considered as being capable of causing population cycles in forest insects, but they may influence the population dynamics of their prey in the low density cycle phase when specialist enemies are largely absent. 2. In the present field study, the total response of the generalist invertebrate predator community to experimentally established pupal densities of the closely related autumnal (Epirrita autumnata) and winter moths (Operophtera brumata) was analysed. 3. Due to the high amount of variation in the dataset, the exact shape of the response curve could not be convincingly estimated. Nevertheless, two important conclusions can be drawn from the analyses. 4. Firstly, the natural invertebrate predator community seems to become saturated at rather low densities of both autumnal and winter moth pupae. Secondly, the predator community seems to become saturated at much lower densities of autumnal than of winter moth pupae. 5. Furthermore, pupal mass was significantly negatively correlated with invertebrate predation probability in autumnal moth pupae. 6. These results indicate that differences in the predator assemblage being able to consume pupae of the two moth species, as well as different handling times, could be responsible for the substantially higher predation rates in winter than in autumnal moth pupae. 7. As a consequence, the population dynamics of autumnal moths might be less affected by generalist invertebrate predators than those of winter moths, as autumnal moths seem able to escape from the regulating influence of generalist predators at much lower population densities than winter moths

Reversed impacts by specialist parasitoids and generalist predators may explain a phase lag in moth cycles : a novel hypothesis and preliminary field tests

Among cyclic populations of herbivores, inter-specific temporal synchrony has been attributed to both climatic factors and trophic interactions. In northern Europe, winter and autumnal moths undergo regular 9–11 year population cycles. The winter moth cycle has typically been phase-locked with that of the autumnal moth, but with a 1–3- year phase lag. We examined potential effects of natural enemies on this phase lag using field experiments and observational data. We found that larval parasitism was significantly higher in autumnal than in winter moths. Conversely, pupal predation by generalist invertebrates was clearly greater in winter than in autumnal moths. The difference in parasitism rates may contribute to the earlier collapse of the autumnal moth cycle. In addition, the phase lag may be strengthened by higher pupal mortality in winter moths in the early increase phase of the cycles. As a consequence, we put forward a hypothesis on reversed effects of natural enemies, providing a potential explanation for phase-lagged population cycles of these moth species

Multi-objective optimization shapes ecological variation

Ecological systems contain a huge amount of quantitative variation between and within species and locations, which makes it difficult to obtain unambiguous verification of theoretical predictions. Ordinary experiments consider just a few explanatory factors and are prone to providing oversimplified answers because they ignore the complexity of the factors that underlie variation. We used multi-objective optimization (MO) for a mechanistic analysis of the potential ecological and evolutionary causes and consequences of variation in the life-history traits of a species of moth. Optimal life-history solutions were sought for environmental conditions where different life stages of the moth were subject to predation and other known fitness-reducing factors in a manner that was dependent on the duration of these life stages and on variable mortality rates. We found that multi-objective optimal solutions to these conditions that the moths regularly experience explained most of the life-history variation within this species. Our results demonstrate that variation can have a causal interpretation even for organisms under steady conditions. The results suggest that weather and species interactions can act as underlying causes of variation, and MO acts as a corresponding adaptive mechanism that maintains variation in the traits of organisms

Shifting body weight-fecundity relationship in a capital breeder : maternal effects on egg numbers of the autumnal moth under field conditions

In the literature, various environmental factors are described as being capable of influencing the reproductive output of insect females irrespective of their body size. Still, female body size or weight is widely used as a proxy for fecundity. In the present study, a seven-year data set on the autumnal moth, Epirrita autumnata (Borkhausen) (Lepidoptera: Geometridae), was used to analyze whether the body weight-fecundity relationship in this capital breeding, cyclic forest defoliating lepidopteran is constant across years. Ambient temperature conditions and density of conspecifics during larval development, the length of the pupal period, as well as moth densities in the parent generation were examined as factors capable of modifying the body weight-fecundity relationship. While the regression slope of potential fecundity (total egg numbers per female) on pupal mass was constant across years, the mean total egg number per given body weight (the regression intercept) was significantly different between years. This residual variance in egg numbers after controlling for the effect of pupal mass was best explained by the pooled geometrid density (autumnal and winter moths) in the parent generation. The total egg number per given body weight decreased with increasing density of geometrid moths in the parent generation. Thus, maternal density effects on offspring fecundity were found in this system. Their rather weak nature suggests, however, that this maternal effect alone does not have the potential of causing cyclic population dynamics in the autumnal moth

Local outbreaks of Operophtera brumata and Operophtera fagata cannot be explained by low vulnerability to pupal predation

One of the unresolved questions in studies on population dynamics of forest Lepidoptera is why some populations at times reach outbreak densities, whereas others never do. Resolving this question is especially challenging if populations of the same species in different areas or of closely-related species in the same area are considered. The present study focused on three closely-related geometrid moth species, autumnal Epirrita autumnata, winter Operophtera brumata and northern winter moths Operophtera fagata, in southern Finland. There, winter and northern winter moth populations can reach outbreak densities, whereas autumnal moth densities stay relatively low. We tested the hypothesis that a lower vulnerability to pupal predation may explain the observed differences in population dynamics. The results obtained do not support this hypothesis because pupal predation probabilities were not significantly different between the two genera within or without the Operophtera outbreak area or in years with or without a current Operophtera outbreak. Overall, pupal predation was even higher in winter and northern winter moths than in autumnal moths. Differences in larval predation and parasitism, as well as in the reproductive capacities of the species, might be other candidates

Trophic interactions and cyclic population dynamics of the autumnal moth: the importance of hymenopteran parasitoids

Siirretty Doriast

Irrationaalisten sijoittajien käyttäytymisen vaikutus arvopapereiden hintoihin

This thesis analyzes the effect that investors’ sentiment and overconfidence have on asset prices. Five interrelated essays examine the effect that the changes in U.S. small investor sentiment or the potential overconfidence of market participants in Nordic financial electricity market have on asset prices. The three first essays analyze the effect of changes in irrational investors’ sentiment on future U.S. equity market returns, both on the aggregate and cross-sectional level. The essays employ information from Google search volumes as a potential tool to gauge a new U.S. small investor sentiment. The first essay finds that increase in positive (negative) information retrieval in Google is associated with positive (negative) future returns on the S&P 500 index. The second and third essays find that positive (negative) unexpected changes in the new U.S. small investor sentiment predict not only positive (negative) future U.S. equity market returns, but also positive (negative) subsequent size and value premiums. The fourth and fifth essays examine the effect of investors’ potential overconfidence on option pricing in the Nordic financial electricity market. The fourth essay finds that the market participants are willing to overpay ex-ante for certain type of option contracts. The fifth essay also finds a seasonality effect in the ex-ante pricing of option con-tracts. Both, the investors’ willingness to overpay and the seasonality in the ex-ante pricing of option contracts, might suggest that the irrational investors are overconfident about the precision of their private information.Väitöskirjan viisi esseetä käsittelevät sijoittajien sentimentin sekä liiallisen itsevarmuuden vaikutusta arvopapereiden hintoihin. Tutkimuksissa analysoidaan amerikkalaisten piensijoittajien sentimentin muutosten tai Pohjoismaiden sähköpörssin markkinaosapuolien liiallisen itsevarmuuden potentiaalisia vaikutuksia arvopapereiden hintoihin. Ensimmäisessä kolmessa esseessä analysoidaan irrationaalisten sijoittajien sentimenttimuutosten yhteyttä Yhdysvaltojen osakemarkkinoiden tuleviin tuottoihin, hyödyntämällä informaatiota Google-hakusanoista. Ensimmäinen esseen tulokset osoittavat, että kasvu positiivisessa (negatiivisessa) tiedonhaussa ennakoi positiivisia (negatiivisia) odotettuja tuottoja S&P 500 -indeksille. Toisessa ja kolmannessa esseessä havaitaan, että positiivinen (negatiivinen) odottamaton muutos amerikkalaisten piensijoittajien sentimentissä ei ennakoi pelkästään osakemarkkinatuottoja Yhdysvalloissa, vaan niillä on myös positiivinen (negatiivinen) yhteys tuleviin koko- ja arvopreemioihin Yhdysvaltojen osakemarkkinoilla. Neljännessä ja viidennessä esseessä tutkitaan sijoittajien liiallisen itsevarmuuden potentiaalista vaikutusta Pohjoismaisen sähköpörssin hinnoitteluun. Neljännessä esseessä tulokset osoittavat, että sijoittajat ovat valmiita maksamaan ylihintaa tietynlaisista optioista. Viidennen esseen tulokset osoittavat lisäksi, että optioiden ylihinnoittelussa esiintyy myös kausivaihtelua. Tietynlaisten optioiden ylihinnoittelu sekä kausivaihtelu voivat viitata siihen, että sijoittajat ovat liian itsevarmoja heidän yksityisen informaationsa tarkkuudesta.fi=vertaisarvioitu|en=peerReviewed