Dissertations / Theses on the topic 'Insect ecology'

Thesis (doctoral)--Swedish University of Agricultural Sciences, 2002.
Thesis documentation sheet inserted. Appendix reprints three manuscripts and one published paper, three of which are co-authored with others. Includes bibliographical references. Also issued electronically via World Wide Web in PDF format; PDF version lacks abstract, ack., and appendix. One ill. in PDF version is in col.

Metapopulation ecology has developed to explain the population dynamics that occur in spatially structured landscapes. In this study, I combined an empirical laboratory approach, using metapopulation microcosms of Callosobruchus maculatus and its endospecific parasitoid Anisopteromalus calandrae, with mathematical population models in order to investigate several fundamental metapopulation processes. Population dynamics in these systems can be studied at two scales; the local patch-wise scale and the regional metapopulation scale. Here I demonstrate that in both homogeneous and heterogeneous landscapes knowledge of local scale demographic processes is necessary in order to understand regional metapopulation dynamics. The differences in the rate and net direction of dispersal between patches as a result of the permeability of the matrix in homogeneous systems and density-dependent dispersal in heterogeneous systems were also explored. Metapopulation dynamics rely on a balance between local extinctions and recolonisations. Therefore, increasing local mortality rates is likely to be detrimental to the persistence of the system. Here, the impact of several common harvesting strategies on the persistence of a host-parasitoid metapopulation was examined. Contrary to expectation I discovered that harvesting in these systems increased both local and regional population sizes. The increased population size as a result of increased mortality was explained in terms of a hydra effect, where harvesting relaxed density-dependence acting on local host populations. The results presented in this thesis are relevant for the monitoring, management and conservation of natural metapopulations and the development of sustainable harvesting strategies in structured landscapes.

Heritable bacterial endosymbionts are responsible for much phenotypic diversity in insects. Mutualists drive large-scale processes such as niche invasion, speciation and mass resistance to natural enemies. However, to persist, mutualists need to be able to transmit with high fidelity from one generation to the next, to be able to express their beneficial phenotypes, and for the benefits they grant the host to outweigh their costs. The effect of ecologically-relevant environmental temperature variations upon transmission and phenotype is a poorly understood area of endosymbiont biology, as is how the symbiont’s cost varies under ecological stress. In this thesis, I examined these parameters for Spiroplasma strain hy1, a defensive mutualist which protects the cosmopolitan, temperate fruit fly Drosophila hydei from attack by a parasitoid wasp. I detected Spiroplasma hy1 in D. hydei individuals from the south of the U.K. The bacterium is at low prevalence compared to hy1 in other localities such as North America and Japan, but its presence in this temperate region conflicts with past studies indicating high sensitivity to low temperatures. I first demonstrate that the vertical transmission of Spiroplasma hy1 is more robust to the cool temperatures typical of temperate breeding seasons than previously considered, with transmission in a ‘permissive passage’ experiment occurring at high fidelity for two generations at a constant 18°C and in an alternating 18/15°C condition. Secondly, I demonstrate that the expression of the defensive phenotype is considerably more sensitive to cool temperatures than transmission. Spiroplasma hy1 protection ceases at 18°C, suggesting that for much of the D. hydei breeding season in areas such as the U.K., hy1 may be selectively neutral in many fly individuals. Finally, I show that hy1 has an unusually low standing cost to its host under starvation stress, contrasting with findings for the related MSRO strain in D. melanogaster. Measures of active cost – the fate of survivors of attack – were unclear. These results indicate that sensitivity to cold temperatures could account for hy1’s low U.K. prevalence. Small amounts of segregational loss could partially counteract selection upon natural enemy resistance, and loss of phenotypic expression at 18°C almost certainly causes hy1 to be neutral at best for parts of early summer and autumn. Future work should investigate the effects of different temperature on costs of symbiont carriage, and whether cool temperatures could push hy1 from mutualism and neutral commensalism to parasitism, as well as investigate how nuclear-mediated anti-wasp protection might interact and compete with hy1-mediated protection.

Cities are novel and fast changing environments. We have little understanding of how urbanisation affects ecological patterns and processes. In Chapter One I review the literature (with an emphasis on arthropods) concerning the general effects of urbanisation on biodiversity, how urban greenspaces are structured, the main characteristics of urban ecological populations and communities, and how trophic dynamics and species interactions are affected by urban environments. The experimental chapters of this thesis focuses on addressing gaps in knowledge concerning how species interactions respond to increasing levels of urbanisation, by using aphids and their natural enemies and ant mutualists as a model system. In Chapter Two I explore the local and fine scale environmental drivers of naturally occurring assemblages of aphids, and their coccinelid and syrphid predators, in urban gardens. Ladybirds are the only group affected by increased urbanisation, while aphids and hoverflies vary as a function of host plant abundance and garden plant richness, which in themselves are indirect consequences of urbanisation. In Chapter Three, I investigate the main biotic and abiotic factors that affect the recruitment of naturally occurring predators, parasitoids and mutualists in experimental colonies placed on an urbanisation gradient. In Chapter Four, I build on this to consider how two aphid species, each differentially attended by mutualists, are influenced by urbanisation. In both chapters I found a higher sensitivity of predators to increased urbanisation, while ants appear to particularly benefit from the creation of these novel habitats. In Chapter Five I explore if there is a differential response of predator functional groups to urban green spaces, and I confirm my hypothesis that specialist predators respond more strongly to increased abundance and size of green space in urban areas. In Chapter Six I investigate which features of urban habitats have a greater influence in the outcome of interspecific competition, and my results suggest that an increased abundance of ants in urban habitats may act in concert with abiotic features of urbanisation to affect the dynamics of competition synergistically. In the seventh and final chapter, I discuss the main findings, contributions and future directions in the field of urban ecology.

The planthopper Prokelisia marginata Van Duzee is native to the eastern coast of North America, where densities on its foodplant, the cordgrass Spartina alterniflora, frequently exceed several thousand per square metre. It has little impact on its host plant in its native range where both species have co-evolved, however where the plant has been introduced and has had no recent exposure to the planthopper, it has a major impact and has been trialled as a biological control agent. P. marginata was recorded for the first time in Britain in 2008, where it feeds primarily on the widespread S. anglica, itself listed as one of the world's 100 worst invasive species, as well as its progenitors S. alterniflora, S. maritima and S. x townsendii. P. marginata appears to be in the successful early stages of invasion in Britain, having already spread extensively. Significantly outnumbering all other saltmarsh arthropod groups, it is benefitting from partial natural enemy escape, and a high proportion of macropterous individuals in all populations indicates strong potential for further range expansion. Utilising both glasshouse and field manipulations, I show that exposure to P. marginata has a significant negative impact on S. anglica, an interaction which has the potential to destabilise Britain's important saltmarsh habitat. I suggest that the four host species that occur in Britain represent a ‘gradient' of shared co-evolutionary history with the planthopper. I show that, whilst all species are negatively impacted by P. marginata exposure, S. alterniflora, the species with which it shares the longest co-evolutionary history, is the least affected. I further show that P. marginata exhibits a preference for, and performs better on, S. anglica. As S. anglica is by far the most abundant of the four Spartina species in Britain, these results suggest P. marginata may be undergoing rapid evolution in its new range to take advantage of this widespread host species, thereby maximising its potential for further range expansion.

The aim of this thesis is to gain a better understanding of the constraints that affect insect adhesion with an emphasis on biological constraints such as plant defences against insects and the influence of abiotic factors on insect foraging. In chapter one of this theses, a literature review on the mechanisms of insect adhesion, the influence of attachment capabilities on foraging behaviour, plant-insect interactions, and synthetic insect barriers is presented, focusing on hymenoptera and coccinellids as representatives of the two basic insect pad types. In the following chapters we test the four leading hypothesis regarding insect adhesion (Contamination, Fluid absorption, Surface roughness and the effect of Surface Energy), before investigating the role of mechano-sensing via insect antenna on substrate choice and finally probing the link between surface properties and locomotion and adhesion. Throughout this thesis I use species of Hymenoptera and Coccinellids as representative species of the two basic adhesive pad types.

Temperate forest ecosystems are subject to various disturbances including insect agents, drought and fire, which can have profound effects on the structure of the ecosystem for many years after the event. Impacts of disturbance can vary widely, therefore an understanding of the legacies of an event are critical in the interpretation of contemporary forest patterns and those of the near future. The primary objective of this dissertation was to investigate the ecological legacies of drought, beetle outbreak and ensuing wildfire in two different ecosystems. A secondary objective of my research, data development, was motivated by a lack of available data which precluded ecological investigation of each disturbance.

I studied the effects of drought on deciduous and coniferous forest along a forest-shrubland ecotone in the southern portion of the Wyoming Basin Ecoregion. The results show that forests in the region have experienced high levels of cumulative drought related mortality over the last decade. Negative trends were not consistent across forest type or distributed randomly across the study area. The patterns of long-term trends highlight areas of forest that are resistant, persistent or vulnerable to severe drought.

In the second thread of my dissertation, I used multiple lines of evidence to retrospectively characterize a landscape scale mountain pine beetle disturbance from the 1970s in Glacier National Park. The lack of spatially explicit data on this disturbance was a major data gap since wildfire had removed some of the evidence from the landscape. I used this information to assess the influence of beetle severity on the burn severity of subsequent wildfires in the decades after the outbreak. Although many factors contribute to burn severity, my results indicate that beetle severity can positively influence burn severity of wildfire. This is likely due to the change in forest structure in the decades after the outbreak and not as a direct result of tree mortality from the outbreak. The long-term perspective of this study suggests that ecological legacies of high severity disturbance may continue to influence subsequent disturbance for many years after the initial event. This work also provides insight on future disturbance interactions associated with the recent mountain pine beetle outbreak that has impacted tens of millions of hectares in western North America over the last two decades.

Root-feeding insects can have top-down influence on vegetative composition and ecosystem processes; however, they may respond to bottom-up factors such as soil resources, site productivity, and disturbance.  My research addressed the following questions: (1) Do disturbance (fire), vegetative composition, soil resources, and fine root standing mass influence the structure of root-feeding insect assemblages? (2) What types of roots do root-feeding insects eat, and do they forage selectively?  (3) Do root-feeding insects influence fine root productivity?  To address these questions, I studied root-feeding insect assemblages in longleaf pine wiregrass (Pinus palustris-Aristida stricta) ecosystems of southwestern Georgia, U.S.A.  On a random basis, study sites were burned at least every other year (B), or left unburned (UB) for about 9 years.  Fine root productivity and root-feeding insect abundances were sampled repeatedly across 54 random plots in UB and B sites.  In Chapter 2, I characterized spatial and temporal patterns of root-feeding insect abundance, understory plant composition, soil resource availability, and fine root standing mass within each plot.  Insect population densities were low overall, but abundance, patchiness, and diversity were greater in UB sites.  Abundance patterns were significantly related to vegetative composition.  In Chapter 3, I quantified the diet of root-feeding insects by measuring the natural abundance of carbon (C) and nitrogen (N) stable isotopes in insects and fine roots.  Using 13C abundance, I examined the contribution of warm season grass roots to insect diet, relative to the proportion of warm season grass roots within adjacent root standing crop samples; 15N abundance was used to detect omnivory.  Overall, insects appeared to be non-selective herbivores and omnivores that may alter foraging behavior to maintain a mixed diet (i.e. reducing or increasing warm season grass consumption when its abundance was high or low, respectively).  The extent of omnivory varied within and among taxa.  In Chapter 4, I estimated the top-down influence of root-feeding insects on fine root productivity by comparison of ingrowth cores with or without an insecticide treatment.  I detected a weak positive effect of herbivores on the productivity of non-grass fine roots (< 10% of fine root productivity).
Ph. D.

Invasive species are alien to the ecosystem under consideration and cause economic or environmental damage or harm to human health. Two alien insects that fit this description are the brown marmorated stink bug, Halyomorpha halys and the spotted lanternfly, Lycorma delicatula. Both invaders are polyphagous pests that feed on a myriad of plant species and inflict severe crop losses. As sustainable control methods depend on the accurate monitoring of species’ invasion and involve the use of natural enemies, we addressed these two facets by exploring novel monitoring techniques and deciphering host-parasitoid interactions for improved integrated pest management. Thus, we adopted ‘BugMap’, a citizen science initiative that enables students, farmers and everyday citizens to report sightings of H. halys from Italy, with emphasis on Trentino-Alto Adige. Aside from fostering citizen participation in scientific endeavors and the enhanced literacy that ensues, BugMap helped uncover the invasion dynamics of H. halys and forecast its potential distribution in Trentino, all while coordinating technical monitoring and informing management strategies. The most promising agent currently under study for the classical biological control of H. halys is the Asian egg parasitoid Trissolcus japonicus. To assess the wasp’s potential non-target impacts, we investigated its foraging behavior in response to chemical traces ‘footprints’ deposited by its main host H. halys and by a suboptimal predatory species, the spined soldier bug, Podisus maculiventris. Wasps exhibited a ‘motivated searching’ when in contact with footprints originating from both species. However, T. japonicus arrestment was significantly stronger in response to H. halys footprints, compared with P. maculiventris, implying the presence of underlying chemical cues that shape its natural preferences. A series of GC-MS chemical analyses revealed that n-tridecane and (E)-2-decenal were more abundant in H. halys footprints and are probably the key components utilized by the wasp for short range host location. The function of the aforementioned compounds was studied, n-tridecane acted as an arrestant, prolonging T. japonicus residence time, whereas (E)-2-decenal fulfilled its presumed defensive role and repelled the wasp. These results shed new light on the chemical ecology of T. japonicus and help expand the understanding of parasitoid foraging and its implications for classical biological control. Moving to the other invader L. delicatula, an egg parasitoid Anastatus orientalis was reported attacking it at high rates in its native range in Eastern Asia and may play a key role in reducing its populations there. A series of bioassays revealed that wasps responded to footprints deposited by L. delicatula gravid females by initiating a strong searching behavior. Moreover, A. orientalis preferred to oviposit in egg masses with intact oothecae, suggesting that the host’s egg covering functions as a trigger for A. orientalis probing and oviposition. Thus, A. orientalis not only overcomes, but also reverses an important line of host structural defense for its own fitness gains. This dissertation discusses the benefits of combining citizen science with traditional monitoring, and the usefulness of decoding host-parasitoid interactions to design more efficacious management strategies of invasive insect pests.

Many species of farmland birds have shown huge declines in numbers and range since the 1970s due to agricultural intensification, and these declines have been worst amongst granivorous species. Recent studies have suggested that low abundance of invertebrate chick food may have been important in driving the declines of a number of granivorous species, however causation has still only been proved for the Grey Partridge, whose decline has been attributed to low chick survival due to the indirect effects of herbicides reducing invertebrate abundance. We investigated invertebrate declines and how they may have affected farmland bird populations in a number of ways. There is little long-term data on abundance of farmland invertebrates. Thus we first looked at how representative data from a long-running suction trap was of invertebrate abundance on local farmland. Suction trap catches reflected abundance of aerial invertebrates on local farmland, and also to abundance of epigeal invertebrates in many cases, particularly abundances in predominant crop types. Secondly, we looked at spatial and temporal distribution of invertebrates on farmland in order to make recommendations about how to increase invertebrate availability to farmland bird populations. Field margins were by far the most invertebrate rich habitats sampled. Most differences in invertebrate abundance between different crop types were found early in the season, at this time spring barley and spring oilseed rape had very low abundances. Winter wheat had relatively high invertebrate abundance compared to spring barley at this time. Winter oilseed rape and set-aside had relatively high abundances of the crop types sampled. We investigated how low invertebrate abundance may have affected populations of granivorous passerines by looking for evidence of reproductive trade-offs in a population of Tree Sparrows, and by supplementary feeding experiments with Tree Sparrow and Yellowhammer chicks. There was no evidence for reproductive trade-offs within years, conversely an effect of individual quality was found. There was some evidence of reproductive trade-offs between years. Supplementary feeding increased the mass of Tree Sparrow first broods early in May but not later in May, and also of chicks with yearling parents, who had a lower provisioning rate. Chicks fledged early in May had a lower survival rate to the following year than chicks fledged later, supplementary feeding and parental age had no effect on chick survival. Supplementary feeding a parent's first brood had no effect on their later reproductive output that season, or on their survival to the next breeding season. Supplementary feeding Yellowhammer chicks early season increased their mass, but had no effect later in the season. This complies with results from a previous study of Yellowhammers in southern England, which showed that a higher proportion of chicks fledge late in the season. Further analysis of this data showed that this was because chicks were more likely to starve early in the season, and also that chick mass was lower early season, even when just looking at chicks which went on to fledge. Thus, it would appear that low invertebrate abundance was affecting the granivorous passerines looked at most in the early season, and through chick mass and survival. Measures to increase invertebrate abundance at this time would be beneficial to populations of granivorous passerines.

Invasive species are alien to the ecosystem under consideration and cause economic or environmental damage or harm to human health. Two alien insects that fit this description are the brown marmorated stink bug, Halyomorpha halys and the spotted lanternfly, Lycorma delicatula. Both invaders are polyphagous pests that feed on a myriad of plant species and inflict severe crop losses. As sustainable control methods depend on the accurate monitoring of species’ invasion and involve the use of natural enemies, we addressed these two facets by exploring novel monitoring techniques and deciphering host-parasitoid interactions for improved integrated pest management. Thus, we adopted ‘BugMap’, a citizen science initiative that enables students, farmers and everyday citizens to report sightings of H. halys from Italy, with emphasis on Trentino-Alto Adige. Aside from fostering citizen participation in scientific endeavors and the enhanced literacy that ensues, BugMap helped uncover the invasion dynamics of H. halys and forecast its potential distribution in Trentino, all while coordinating technical monitoring and informing management strategies. The most promising agent currently under study for the classical biological control of H. halys is the Asian egg parasitoid Trissolcus japonicus. To assess the wasp’s potential non-target impacts, we investigated its foraging behavior in response to chemical traces ‘footprints’ deposited by its main host H. halys and by a suboptimal predatory species, the spined soldier bug, Podisus maculiventris. Wasps exhibited a ‘motivated searching’ when in contact with footprints originating from both species. However, T. japonicus arrestment was significantly stronger in response to H. halys footprints, compared with P. maculiventris, implying the presence of underlying chemical cues that shape its natural preferences. A series of GC-MS chemical analyses revealed that n-tridecane and (E)-2-decenal were more abundant in H. halys footprints and are probably the key components utilized by the wasp for short range host location. The function of the aforementioned compounds was studied, n-tridecane acted as an arrestant, prolonging T. japonicus residence time, whereas (E)-2-decenal fulfilled its presumed defensive role and repelled the wasp. These results shed new light on the chemical ecology of T. japonicus and help expand the understanding of parasitoid foraging and its implications for classical biological control. Moving to the other invader L. delicatula, an egg parasitoid Anastatus orientalis was reported attacking it at high rates in its native range in Eastern Asia and may play a key role in reducing its populations there. A series of bioassays revealed that wasps responded to footprints deposited by L. delicatula gravid females by initiating a strong searching behavior. Moreover, A. orientalis preferred to oviposit in egg masses with intact oothecae, suggesting that the host’s egg covering functions as a trigger for A. orientalis probing and oviposition. Thus, A. orientalis not only overcomes, but also reverses an important line of host structural defense for its own fitness gains. This dissertation discusses the benefits of combining citizen science with traditional monitoring, and the usefulness of decoding host-parasitoid interactions to design more efficacious management strategies of invasive insect pests.

This thesis is an exciting avenue of research that broadens our understanding of the ecological relationship between microbes and herbivorous insects and applies this knowledge to the development of new "attract and kill" technologies in insect pest management. The outcomes of the research will help improve existing control practices for Carpophilus beetles, which are major pests in Australian horticulture, and pave the way for developing novel tools and practices for monitoring and controlling newly established insect pests.

Thesis (Ph.D.)--Michigan State University. Dept. of Entomology and Program in Ecology, Evolutionary Biology, and Behavior, 2008.
Title from PDF t.p. (viewed on July 17, 2009) Includes bibliographical references (p. 115-126). Also issued in print.

The study of aposematic coloration and mimicry has a long and distinguished history, and has stimulated scientific inquiry in areas as diverse as chemistry, evolution, ecology, and behavior. Yet, many questions regarding signal function and ecological dynamics remain unknown. This dissertation attempts to address some of these questions about how a visual warning signal functions and how the environment changes its efficacy. First, I evaluated the role of luminance contrast in aposematic signaling using milkweed bugs as model prey and Chinese mantids as model predators. Predators learned to avoid unpalatable prey sooner and remembered to avoid unpalatable prey for longer when the prey had higher luminance contrast with the background. These results help define what makes a visual signal conspicuous and designate the importance of high luminance contrast in the efficacy of a warning color signal. Another important characteristic of warning coloration is the reason for the advertisement. I was able to identify and quantify the toxic compounds in both the host plant and the viceroy butterfly, a putative aposematic insect. These results provide a chemical mechanism for previous research that demonstrated that the viceroy was unpalatable to avian predators. Next, I was able to test the role of geographic variation in host plant and viceroy chemical defense and how that variation compared with the local abundance of a mimicry co-model of the viceroy, the queen butterfly. The results indicated the viceroy was more chemically defended and more unpalatable in locations where the queen was at low abundances. This result suggests that mimicry evolves in a geographic mosaic of co-evolution. Finally, I used molecular phylogenetic approaches to reconstruct and test the evolution of mimicry in the North American admiral butterflies (Limenitis: Nymphalidae). One species, L. arthemis, evolved the black, pipevine swallowtail mimetic form but later reverted to the white-banded ancestral form. This character reversion is strongly correlated with the geographic absence of the model species and its host plant, not the mimics host plant distribution. These results support the idea that loss of model in a geographic area is not an evolutionary stopping point for a Batesian mimic.

Thesis (doctoral)--Swedish University of Agricultural Sciences, 2003.
Thesis documentation sheet inserted. Includes appendix of four papers and manuscripts, two co-authored with Barbara Ekbom. Includes bibliographical references. Also partially issued electronically via World Wide Web in PDF format; online version lacks appendix of papers.

Thesis (PhD)--Macquarie University, Division of Environmental and Life Sciences, Dept. of Biological Sciences, 2005.
Bibliography: p. 178-203.
Introduction -- Study sites -- Leaf characteristics and resource availability -- Insect herbivory and resource availability -- Insect communities and resource availability -- Influence of resource availability on recovery from herbivory -- Conclusions.
This project used the resource availability hypothesis (Coley et al., 1985) as a framework for investigating the relationship between resource availability (as defined by soil nutrients), leaf traits, insect herbivore damage and insect community structure. According to the hypothesis, plants from low resource environments should be better-defended, have longer leaf lifespans and slower growth rates than plants from higher resource environments. Higher resource plant species are expected to suffer higher levels of herbivory and recover faster from herbivory than low resource plant species (Coley et al. 1985). A corollary to this hypothesis is that plants from higher resource sites should support greater densities of insect herbivores than low resource species. Comparisons between high and low resource sites were made in terms of: (i) leaf traits of mature and immature leaves; (ii) phenology of leaf maturation; (iii) herbivore damage in the field and laboratory; (iv) diversity and abundance of herbivorous insect fauna; and (v) ability to recover from herbivory.
Mode of access: World Wide Web.
243 p. ill., maps

Les plagues d’insectes són elements integrats a la dinàmica del paisatge forestal. Tot i això, durant les últimes dècades, han experimentat un augment en nombre i impacte, implicant conseqüències severes pels ecosistemes i la societat. Els motius d’aquesta dinàmica són principalment els canvis en l’ús del sòl, els canvis en el clima i la introducció d’espècies invasores degut al comerç internacional i a la mobilitat humana. L’objectiu central d’aquesta tesi és avançar en el coneixement de l’impacte de les plagues d’insectes al paisatge forestal i integrar-lo en eines de modelització que ajuden a la predicció de conseqüències en un futur canviant. Hem basat l’aproximació en definir els efectes directes i indirectes de les plagues d’insectes mitjançant la descripció de les interaccions amb altres pertorbacions del paisatge forestal (el foc, la sequera, les tempestes, la contaminació, etc.) i descriure els mecanismes que hi influeixen. Hem exemplificat el paper de les plagues forestals amb el cas d’estudi de la papallona del boix (Cydalima perspectalis), un lepidòpter originari d’Àsia i invasor a Europa des de 2007. Hem descrit el nínxol ecològic de l’espècie així com la seva distribució i impacte potencial a l’àrea d’invasió. Finalment hem anticipat els impactes d’aquesta plaga i les seves interaccions amb altres pertorbacions a la vessant sud dels Pirineus en un futur regit pel canvi climàtic. Aquesta tesi proposa diferents metodologies per a l’estudi de les plagues forestals i el seu impacte al paisatge. Primer es demostra que per una correcta aplicació dels Species Distribution Models (SDM) en espècies invasores és necessària la combinació d’informació de la zona nativa i la zona d’invasió. Segon, s’ha evidenciat que els models de simulació espacialment explícits són eines adequades per descriure les pertorbacions forestals, identificar els paràmetres clau de la seva dinàmica, analitzar les seves interaccions i anticipar els seus impactes davant la incertesa del canvi global. Finalment, es constata que per tal de fer una aplicació eficaç de les metodologies descrites és necessari diferenciar l’ocurrència d’una pertorbació de la severitat del seu impacte. Els resultats aquí exposats proporcionen noves evidències dels processos que regeixen la dinàmica de plagues forestals i, en concret, de C. perspectalis. Es demostra que la distribució de C. perspectalis al sud dels Pirineus depèn de la presencia de la planta hoste (Buxus sempervirens) i la capacitat d’expansió de l’insecte (que es veu normalment alterada per introduccions antropocòries involuntàries), mentre que no és limitada per la composició de l’habitat. Tot i això, la defoliació severa només es troba en llocs d’alta adequació climàtica, definida per un rang de temperatures diürnes petit i una baixa estacionalitat de la precipitació i la temperatura. Aquestes condicions defineixen un cert patró de continentalitat on els boixos més susceptibles de ser atacats són aquells que es troben a prop de la costa i a baixa elevació (a les províncies de Girona, Barcelona i Navarra) i excloent zones del Pirineu central (Lleida, Huesca). Les projeccions futures de l’impacte causat per C. perspectalis descriuen una relació de consumidor-recurs cíclica amb l’estat dels boixos. A més el canvi climàtic podria reduir l’àrea d’impacte sever causat per l’insecte concentrant-lo només a algunes localitats. La interacció entre C. perspectalis i altres pertorbacions com el foc i la sequera extrema no ha resultat significativa. Tot i això, tal com he descrit en altres espècies d’insectes forestals, les interaccions amb altres pertorbacions són complexes i es produeixen en diverses direccions, efectes (antagònic i sinèrgic) i escales espacials i temporals. Tota aquesta informació ofereix una base de gran valor per a la futura recerca i pel disseny d’estratègies de gestió de boscos i plagues.
Las plagas de insectos son elementos integrados en la dinámica del paisaje forestal. Sin embargo, durante las últimas décadas, han experimentado un aumento en número e impacto, implicando consecuencias severas para los ecosistemas y la sociedad. Los motivos de esta dinámica son principalmente los cambios en el uso del suelo, los cambios en el clima y la introducción de especies invasoras debido al comercio internacional y la movilidad humana. El objetivo de esta tesis es avanzar en el conocimiento del impacto de las plagas de insectos en el paisaje forestal y integrarlo en herramientas de modelización que ayudan a la predicción de consecuencias en un futuro cambiante. Hemos basado la aproximación al definir los efectos directos e indirectos de las plagas de insectos mediante la descripción de las interacciones con otras perturbaciones del paisaje forestal y describir los mecanismos que influyen. Hemos ejemplificado el papel de las plagas forestales con el caso de estudio de la mariposa del boj (Cydalima perspectalis), un lepidóptero originario de Asia e invasor en Europa desde 2007. Hemos descrito el nicho ecológico de la especie así como la su distribución e impacto potencial en el área de invasión. Finalmente hemos anticipado los impactos de esta plaga y sus interacciones con otras perturbaciones en la vertiente sur de los Pirineos en un futuro regido por el cambio climático. Esta tesis propone diferentes metodologías para el estudio de las plagas forestales y su impacto en el paisaje. Primero se demuestra que para una correcta aplicación de los Species Distribution Modelos (SDM) en especies invasoras es necesaria la combinación de información de la zona nativa y la zona de invasión. Segundo, se ha evidenciado que los modelos de simulación espacialmente explícitos son herramientas adecuadas para describir las perturbaciones forestales, identificar los parámetros clave de su dinámica, analizar sus interacciones y anticipar sus impactos ante la incertidumbre del cambio global. Finalmente, se constata que para hacer una aplicación eficaz de las metodologías descritas es necesario diferenciar la ocurrencia de una perturbación de la severidad de su impacto. Los resultados aquí expuestos proporcionan nuevas evidencias de los procesos que rigen la dinámica de plagas forestales y, en concreto, de C. perspectalis. Se demuestra que la distribución de C. perspectalis al sur de los Pirineos depende de la presencia de la planta huésped (Buxus sempervirens) y la capacidad de expansión del insecto, mientras que no es limitada por la composición del habitat. Sin embargo, la defoliación severa sólo se encuentra en lugares de alta adecuación climática, definida por un rango de temperaturas diurnas pequeño y una baja estacionalidad de la precipitación y la temperatura. Estas condiciones definen un cierto patrón de continentalidad donde los bojes más susceptibles de ser atacados son aquellos que se encuentran cerca de la costa ya baja elevación (en las provincias de Girona, Barcelona y Navarra) y excluyendo zonas del Pirineo central (Lleida, Huesca ). Las proyecciones futuras del impacto causado por C. perspectalis describen una relación de consumidor-recurso cíclica con el estado de los bojes. Además el cambio climático podría reducir el área de impacto severo causado por el insecto concentrándolo sólo a algunas localidades. La interacción entre C. perspectalis y otras perturbaciones como el fuego y la sequía extrema no ha resultado significativa. Sin embargo, tal como he descrito en otras especies de insectos forestales, las interacciones con otras perturbaciones son complejas y se producen en varias direcciones, efectos (antagónico y sinérgico) y escalas espaciales y temporales. Toda esta información ofrece una base de gran valor para la futura investigación y el diseño de estrategias de gestión de bosques y plagas.
Insect pests are integrated elements of forest landscape dynamics. However, an increase in the number of pest outbreaks and in their impact has been experienced in recent decades, causing severe consequences for ecosystems and society. The reasons behind these changing dynamics are mainly related to changes in land-use, climate, and the introduction of invasive species due to international trades and human mobility. The central goals of this thesis are to advance in the understanding of insect pest impacts on forest landscapes and to integrate them in modelling tools that help the prediction of consequences in a global change future. To face these goals, I defined the direct and indirect effects of insect pests and their interactions with other forest landscape disturbances (fire, drought, storms, pollution, etc.), and described the mechanisms underlying these responses. Aiming at working on a specific actual concerning pest, I examined the case of boxwood moth (Cydalima perspectalis), a Lepidoptera native to Asia and invasive in Europe since 2007. I described the ecologic niche of the species as well as its distribution and potential impact on the invaded area. Finally, I anticipated impacts of this pest and its interactions with other disturbances in the Southern Pyrenees under future climatic conditions. In this thesis, I proposed different methodologies to study the impact of forest pests. First, I demonstrated that a combination of information from the native and invaded areas is required for a correct application of Species Distribution Models (SDMs) in invasive species. Second, I evidenced that spatially explicit simulation models are appropriate tools for the study of forest disturbances, identifying key parameters in determining their dynamics, analyzing their interactions, and anticipating their impacts in the face of global change uncertainty. Finally, I highlighted the adequacy of differentiating the presence versus the severity of a disturbance in order to effectively apply the methodologies described. The results presented in this thesis provide new evidence of the processes governing pest dynamics – and their associated impacts – on forest functioning, in particular, the case of C. perspectalis. I demonstrated that the distribution of C. perspectalis in the Southern Pyrenees depended on the presence of the host plant (Buxus sempervirens) and the insect spread capacity (which is usually altered by involuntary anthropochory), while it was not limited by the fragmentation or heterogeneity of the habitat. However, severe defoliation was only found in places with high climatic suitability, defined by low seasonal precipitation and temperature, and low temperature diurnal range. These conditions define a continentality pattern where the most endangered boxwoods were those located near the coast and at low elevation (in the provinces of Girona, Barcelona, and Navarra) and excluding areas of the central Pyrenees (Lleida, Huesca). Future projections of C. perspectalis impact describe a cyclic consumer-resource relationship with the host plant. In addition, climate change may reduce the area of severe impact being concentrated only in few locations. The interaction between C. perspectalis and extreme drought was not significant. However, as I reported for other forest pest species, interactions with other disturbances are complex and occur in various directions, effects (antagonistic and synergistic) and spatial and temporal scales. For instance, trees that are damaged by fire or drought can synthesize ethanol, monoterpenes, and pheromones that attract insects; trees killed by an insect pest result in an accumulation of fuel that facilitates the spread of fires; trees weakened by drought have a lower response capacity (resin synthesis, regrowth capacity, etc.) and are therefore more susceptible to insect attacks. All this information offers a valuable basis for future research and for designing forest and pest management actions.
Universitat Autònoma de Barcelona. Programa de Doctorat en Ecologia Terrestre