An established host-parasitoid-hyperparasitoid system was used to investigate how the physiological and behavioural characteristics of parasitoids influence the outcomes of laboratory-based host specificity tests. The characteristics of the two pteromalid egg parasitoids, Enoggera nassaui (Girault) and Neopolycystus insectifurax Girault, were assessed and interpreted in regard to the particular host specificity testing methods used and the control of the eucalypt defoliating beetle Paropsis charybdis Stål (Chrysomelidae) in New Zealand. The physiology of N. insectifurax was examined to determine how to increase production of female parasitoids that were physiologically capable and motivated to parasitise P. charybdis eggs in laboratory trials. Neopolycystus insectifurax were found to be more synovigenic than E. nassaui. Provisioning them with honey and host stimuli for three days, and allowing females to parasitise hosts in isolation (i.e. in the absence of competition) was an effective means of achieving these goals. No-choice tests were conducted in Petri dish arenas with the four paropsine beetles established in New Zealand. All four were found to be within the physiological host ranges of E. nassaui and N. insectifurax, but their quality as hosts, as indicated by the percent parasitised and offspring sex ratios, varied. The results of paired choice tests between three of the four species agreed with those of no-choice tests in most instances. However, the host Trachymela catenata (Chapuis), which was parasitised at very low levels by E. nassaui in no-choice tests, was not accepted by that species in paired choice tests. A much stronger preference by N. insectifurax for P. charybdis over T. catenata was recorded in the paired choice test than expected considering the latter was parasitised at a high level in the no-choice test. The presence of the target host in paired choice tests reduced acceptance of lower ranked hosts. Both no-choice and choice tests failed to predict that eggs of the acacia feeding beetle Dicranosterna semipunctata (Chapuis) would not be within the ecological host range of E. nassaui and N. insectifurax. Behavioural observations were made of interspecific competition between E. nassaui and N. insectifurax for access to P. charybdis eggs. Two very different oviposition strategies were identified. Neopolycystus insectifurax were characterised by taking possession of, and aggressively guarding host eggs during and after oviposition. They also appeared to selectively oviposit into host eggs already parasitised by E. nassaui, but did not emerge from significantly more multi-parasitised hosts than E. nassaui. Enoggera nassaui did not engage in contests and fled when approached by N. insectifurax. Although often prohibited from ovipositing by N. insectifurax, E. nassaui were able to locate and begin ovipositing more quickly, and did not remain to guard eggs after oviposition. It is hypothesised that although N. insectifurax have a competitive advantage in a Petri dish arena, E. nassaui may be able to locate and parasitise more host eggs in the field in New Zealand, where competition for hosts in is relatively low. The biology of the newly established encyrtid Baeoanusia albifunicle Girault was assessed. It was confirmed to be a direct obligate hyperparasitoid able to exploit E. nassaui but not N. insectifurax. Field and database surveys found that all three parasitoids have become established in many climatically different parts of New Zealand. Physiological characteristics were identified that may allow B. albifunicle to reduced effective parasitism of P. charybdis by E. nassaui to below 10%. However, the fact that hyperparasitism still prevents P. charybdis larvae from emerging, and that B. albifunicle does not attack N. insectifurax, may preclude any significant impact on the biological control of P. charybdis. Overall, parasitoid ovigeny and behavioural interactions with other parasitoids were recognised as key characteristics having the potential to influence host acceptance in the laboratory and the successful biological control of P. charybdis in the field. It is recommended that such characteristics be considered in the design and implementation of host specificity tests and might best be assessed by conducting behavioural observations during parasitoid colony maintenance and the earliest stages of host specificity testing.

No description available.

We are currently faced with the global challenge of conserving biological diversity while also increasing food production to meet the demands of a growing human population. Land-use change, primarily resulting from conversion to production land, is currently the leading cause of biodiversity loss. This occurs through habitat loss, fragmentation of remaining natural habitats, and resulting edge effects. Land-sparing and land-sharing approaches have been discussed as alternative ways to engineer landscapes to mitigate biodiversity loss while meeting production objectives. However, these represent extremes on a continuum of real-world landscapes, and it will be important to understand the mechanisms by which adjacent land use affects natural remnant ecosystems in order to make local land-management decisions that achieve conservation, as well as production, objectives. This thesis investigates the impact of juxtaposing production and natural forest on the community-wide interactions between lepidopteran herbivores and their parasitoids, as mediated by parasitoid spillover between habitats. The first and overarching objective was to determine whether herbivore productivity drives asymmetrical spillover of predators and parasitoids, primarily from managed to natural habitats, and whether this spillover alters trophic interactions in the recipient habitat. The study of trophic interactions at a community level requires understanding of both direct and indirect interactions. However, community-level indirect interactions are generally difficult to predict and measure, and these have therefore remained understudied. Apparent competition is an indirect interaction mechanism thought to be very important in structuring host-parasitoid assemblages. However, this is known primarily from studies of single species pairs, and its community-wide impacts are less clear. Therefore, my second objective was to determine whether apparent competition could be predicted for all species pairs within an herbivore assemblage, based on a measure of parasitoid overlap. My third objective was to determine whether certain host or parasitoid species traits can predict the involvement of those species in apparent competition. My key findings were that there is a net spillover of generalist predators and parasitoids from plantation to native forest, and that for generalists, this depends on herbivore abundance in the plantation forest. Herbivore populations across the edge were linked by shared parasitoids in apparent competition. Consequently, an experimental reduction of herbivore density in the plantation forest changed parasitism rates in the natural forest, as predicted based on parasitoid overlap. Finally, several host and parasitoid traits were identified that can predict the degree to which host or parasitoid species will be involved in apparent competition, a finding which may have extensive application in biological control, as well as in predicting spillover edge effects. Overall, this work suggests that asymmetrical spillover between production and natural habitats occurs in relation to productivity differences, with greater movement of predators and parasitoids in the managed-to-natural forest direction. The degree to which this affected species interactions has implications for landscape design to achieve conservation objectives in production landscapes.

Cette étude vise à comparer l’histoire évolutive des parasitoïdes du genre Horismenus (Hymenoptera: Eulophidae) à celle de leurs hôtes bruches (Coleoptera: Bruchidae) et plante hôte (Phaseolus vulgaris L.) cultivée dans le contexte d’agriculture traditionnelle, au sein de son centre de domestication Mésoaméricain. Nous avons analysé la structure génétique de 23 populations de quatre espèces de parasitoïdes au Mexique, en utilisant un fragment du gène mitochondrial COI afin de les comparer aux structures précédemment publiées des hôtes bruches et du haricot commun. Nous avons prédit que les structures génétiques des populations d’hôtes (bruches et plante) et de parasitoïdes seraient similaires puisque également influencées par la migration entremise par l’humain (HMM) étant donnée que les parasitoïdes se développent telles que les bruches à l’intérieur des haricots. Compte tenu des stratégies de manipulation reproductive utilisées par l’alpha-protéobactérie endosymbionte Wolbachia spp. pour assurer sa transmission, la structure génétique des populations de parasitoïdes inférée à partir du génome mitochondrial devrait être altérée conséquemment à la transmission conjointe des mitochondries et des bactéries lors de la propagation de l’infection dans les populations de parasitoïdes. Les populations du parasitoïde H. missouriensis sont infectées par Wolbachia spp. Tel que prédit, ces populations ne sont pas différenciées (FST = 0,06), ce qui nous empêche d’inférer sur une histoire évolutive parallèle. Contrairement aux bruches, Acanthoscelides obtectus et A. ovelatus, la HMM n'est pas un processus contemporain qui influence la structure génétique des populations du parasitoïde H. depressus, étant donné la forte différenciation (FST = 0,34) qui existe entre ses populations. La structure génétique observée chez H. depressus est similaire à celle de sa plante hôte (i.e. dispersion aléatoire historique à partir d'un pool génique ancestral très diversifié) et est probablement le résultat d’un flux génique important en provenance des populations de parasitoïdes associées aux haricots spontanées à proximité des champs cultivés. L’étude de l’histoire évolutive intégrant plusieurs niveaux trophiques s’est avérée fructueuse dans la détection des différentes réponses évolutives entre les membres du module trophique face aux interactions humaines et parasitaires, et montre la pertinence d’analyser les systèmes écologiques dans leur ensemble. / This study aims to compare the evolutionary history of Horismenus parasitoids (Hymenoptera: Eulophidae) to that of their bruchid beetle hosts (Coleoptera: Bruchidae) and their domesticated host plant (Phaseolus vulgaris L.) in the context of traditional agriculture within their Mesoamerican center of domestication. We analyzed the genetic structure of 23 populations of four Horismenus species in Mexico using COI mitochondrial gene fragments and compared the structures to previously published data on bean plant and beetle hosts. We predicted that because parasitoids complete their development within their beetle hosts, within the bean, the genetic structure of both the host and the parasitoid would be similar and equally influenced by human-mediated migration (HMM). Furthermore, because of reproductive manipulation strategies often used by the alpha-proteobacteria endosymbionte Wolbachia spp. to ensure its transmission, the genetic structure of parasitoid populations inferred from mitochondrial genome would be bias consequently to the conjoint transmission of mitochondria and the bacteria according to propagation of the infection within parasitoids populations. The populations of H. missouriensis parasitoids are infected by Wolbachia spp. As predicted, these populations are not differentiated (FST = 0.06) which prevents us to infer on a parallel evolutionary history. Unlike their bruchids hosts, Acanthoscelides obtectus and A. ovelatus, the HMM is not a contemporary process influencing H. depressus population genetic structure according to the strong populations differentiation (FST = 0.34). The genetic structure observed within H. depressus populations is similar to that of its host plant (i.e. historical random dispersal from a highly diversified ancestral gene pool) and is probably the result of extensive gene flow from parasitoids associated with wild beans populations adjacent to crop fields. The study of evolutionary history integrating multitrophic levels has proved to be fruitful in detecting different evolutionary responses among members of the trophic module face to human and parasite interactions, but also points out the pertinence of analyzing ecological systems as a whole.

Le puceron du soya (Aphis glycines) est le ravageur le plus important de la culture du soya en Amérique du Nord. Quoi qu’efficaces, les pesticides permettent le contrôle des ravageurs que pour une courte période et nécessitent plusieurs applications au cours de la saison. De plus, ils sont dommageables pour l’environnement et la santé humaine. La lutte biologique se présente comme une alternative crédible pour le contrôle des populations d’A. glycines en Amérique du Nord. Trois parasitoïdes (Binodoxys communis, Aphidius colemani, Aphelinus certus) du puceron semblent être des candidats prometteurs. L’objectif de cette étude était d’examiner certains attributs biologiques de ces parasitoïdes au Québec. Dans le cas de B. communis et A. certus nous avons estimé leur synchronisme saisonnier ainsi que leur résistance au froid en laboratoire et en conditions naturelles. Dans le cas, d’A. colemani, nous avons évalué sa capacité à parasiter le puceron du soya et à se disperser dans un champ de soya. Nos résultats démontrent que la souche utilisée de B. communis a perdu sa capacité à entrer en diapause, probablement à cause de la longue période d’élevage en laboratoire qui a suivi son échantillonnage en Asie. Aphelinus certus démontre un potentiel intéressant puisqu’il possède un synchronisme saisonnier tant en automne qu’au printemps avec son hôte ainsi qu’un bon potentiel de survie hivernale au Québec. Quant à A. colemani, les essais suggèrent qu’il se disperse rapidement hors des champs sans attaquer de manière significative A. glycines. / The soybean aphid (Aphis glycines) has become the most important pest of soybean in North America. Despite their efficiency, insecticides do eliminate the pest only for short periods and several applications may be required during the growing season. Furthermore, they are detrimental for the environment and human health. Biological control appears as a promising alternative for the control of A. glycines populations in North America. Three parasitoid species (Binodoxys communis, Aphidius colemani, Aphelinus certus) have been identified as potential candidates. The objective of this study was to study some biological attributes of these parasitoids in Québec. For B. communis and A. certus we examined their seasonal activities and their cold hardiness in laboratory and natural conditions. For A. colemani, we evaluated its capacity to parasite the soybean aphid and to disperse in soybean fields. Our results revealed that the B. communis strain we used had lost its capacity to enter diapause, probably due to the long period of laboratory rearing following its sampling in Asia. Aphelinus certus showed an interesting potential because the species is synchronized with its host both in the fall and the spring and has the capacity to overwinter in Québec. For A. colemani, the essays suggest that it disperses rapidly out of the field without attacking significantly A. glycines.

La plasticité phénotypique, i.e. la capacité d’un génotype à exprimer plusieurs phénotypes en fonction des conditions environnementales, représente une source de variabilité phénotypique, et tient donc un rôle majeur dans l’évolution. Dans un environnement variable, les stratégies généralistes, capables de maintenir une valeur d’aptitude phénotypique (fitness) stable sur une plus large gamme de conditions environnementales grâce à une plus grande plasticité de traits sous-jacents, devraient être favorisées. L’analyse de normes de réaction, au laboratoire et en conditions naturelles, de traits physiologiques et de traits liés à la fitness en fonction de la température, révèle chez le parasitoïde Venturia canescens, que (i) la variabilité thermique de l’habitat détermine la forme des normes de réaction selon le compromis entre stratégies généraliste et spécialiste, (ii) les différences entre individus généralistes et spécialistes se maintiennent face à des fluctuations de la température mimant les conditions naturelles et (iii) les individus subissant une plus grande variabilité thermique dans leur habitat possèdent une capacité d’acclimatation au froid plus importante. Ces résultats montrent l’existence de deux stratégies chez V. canescens et donc une différenciation de leur niche thermique, autorisant leur coexistence en environnement hétérogène / Phenotypic plasticity, i.e. the ability of a genotype to express several phenotypes depending on environmental conditions, represents an important source of phenotypic variability and so plays a major role in evolution. In a variable environment, generalist strategies, able to maintain a stable value of fitness over a wide range of environmental conditions, thanks to a greater plasticity of underlying traits, should be favored. The analysis of reaction norms of physiological traits and traits related to fitness as a function of temperature reveals in the parasitoid Venturia canescens that (i) thermal variability of the habitat determines the shape of reaction norms, according to the trade-off between generalist and specialist strategies, (ii) differences between generalist and specialist individuals are maintained face to rapid fluctuations in temperature that mimic natural conditions and (iii) individuals experiencing greater variability in their thermal habitat have a greater capacity for cold acclimation. These results indicate the existence of two different strategies in V. canescens and therefore a thermal niche differentiation, allowing their coexistence in a heterogeneous environment

This dissertation is concerned with effects dispersal and forest structure on forest insect population dynamics, and with identifying generating processes by comparing observed patterns to model predictions. In chapter 2, we investigated effects of changing forest landscape patterns on integro-difference models of host-parasitoid population dynamics. We demonstrated that removing habitat can increase herbivore density when herbivores don't disperse far, and parasitoids disperse further, due to differences in dispersal success between trophic levels. This is a novel potential explanation for why forest fragmentation increases the duration of forest tent caterpillar outbreaks. To better understand spatial model behaviour, we proposed a new local variation of the dispersal success approximation. The approximation successfully predicts effects of habitat loss and fragmentation on realistically complex landscapes, except when outbreak cycle amplitude is very large. Local dispersal success is useful in part because parameters can be estimated from widely available habitat data. In chapter 3, we investigated how well a discretized integro-difference model of mountain pine beetle population dynamics predicted the occurrence of new infestations in British Columbia. We found that a model with a large dispersal kernel, and high emigration from new, low severity infestations yielded the best predictions. However, we do not believe this to be convincing evidence that many beetles disperse from new, low severity infestations. Rather, we argued that differences in habitat quality, detection errors, and Moran effects can all confound dispersal patterns, making it difficult to infer dispersal parameters from observed infestation patterns. Nonetheless, predicting infestation risk is useful, and large kernels improve predictions. In chapter 4, we used generalized linear mixed models to characterize spatial and temporal variation in the propensity of jack pine trees to produce pollen cones, and account for confounding effects on the relationship between pollen cone production and previous defoliation by jack pine budworm. We found effects of stand age, and synchronous variation in pollen cone production among years. Accounting for background patterns in pollen cone production clarified that pollen cone production declines in with previous defoliation, as expected.

Cette étude vise à comparer l’histoire évolutive des parasitoïdes du genre Horismenus (Hymenoptera: Eulophidae) à celle de leurs hôtes bruches (Coleoptera: Bruchidae) et plante hôte (Phaseolus vulgaris L.) cultivée dans le contexte d’agriculture traditionnelle, au sein de son centre de domestication Mésoaméricain. Nous avons analysé la structure génétique de 23 populations de quatre espèces de parasitoïdes au Mexique, en utilisant un fragment du gène mitochondrial COI afin de les comparer aux structures précédemment publiées des hôtes bruches et du haricot commun. Nous avons prédit que les structures génétiques des populations d’hôtes (bruches et plante) et de parasitoïdes seraient similaires puisque également influencées par la migration entremise par l’humain (HMM) étant donnée que les parasitoïdes se développent telles que les bruches à l’intérieur des haricots. Compte tenu des stratégies de manipulation reproductive utilisées par l’alpha-protéobactérie endosymbionte Wolbachia spp. pour assurer sa transmission, la structure génétique des populations de parasitoïdes inférée à partir du génome mitochondrial devrait être altérée conséquemment à la transmission conjointe des mitochondries et des bactéries lors de la propagation de l’infection dans les populations de parasitoïdes. Les populations du parasitoïde H. missouriensis sont infectées par Wolbachia spp. Tel que prédit, ces populations ne sont pas différenciées (FST = 0,06), ce qui nous empêche d’inférer sur une histoire évolutive parallèle. Contrairement aux bruches, Acanthoscelides obtectus et A. ovelatus, la HMM n'est pas un processus contemporain qui influence la structure génétique des populations du parasitoïde H. depressus, étant donné la forte différenciation (FST = 0,34) qui existe entre ses populations. La structure génétique observée chez H. depressus est similaire à celle de sa plante hôte (i.e. dispersion aléatoire historique à partir d'un pool génique ancestral très diversifié) et est probablement le résultat d’un flux génique important en provenance des populations de parasitoïdes associées aux haricots spontanées à proximité des champs cultivés. L’étude de l’histoire évolutive intégrant plusieurs niveaux trophiques s’est avérée fructueuse dans la détection des différentes réponses évolutives entre les membres du module trophique face aux interactions humaines et parasitaires, et montre la pertinence d’analyser les systèmes écologiques dans leur ensemble. / This study aims to compare the evolutionary history of Horismenus parasitoids (Hymenoptera: Eulophidae) to that of their bruchid beetle hosts (Coleoptera: Bruchidae) and their domesticated host plant (Phaseolus vulgaris L.) in the context of traditional agriculture within their Mesoamerican center of domestication. We analyzed the genetic structure of 23 populations of four Horismenus species in Mexico using COI mitochondrial gene fragments and compared the structures to previously published data on bean plant and beetle hosts. We predicted that because parasitoids complete their development within their beetle hosts, within the bean, the genetic structure of both the host and the parasitoid would be similar and equally influenced by human-mediated migration (HMM). Furthermore, because of reproductive manipulation strategies often used by the alpha-proteobacteria endosymbionte Wolbachia spp. to ensure its transmission, the genetic structure of parasitoid populations inferred from mitochondrial genome would be bias consequently to the conjoint transmission of mitochondria and the bacteria according to propagation of the infection within parasitoids populations. The populations of H. missouriensis parasitoids are infected by Wolbachia spp. As predicted, these populations are not differentiated (FST = 0.06) which prevents us to infer on a parallel evolutionary history. Unlike their bruchids hosts, Acanthoscelides obtectus and A. ovelatus, the HMM is not a contemporary process influencing H. depressus population genetic structure according to the strong populations differentiation (FST = 0.34). The genetic structure observed within H. depressus populations is similar to that of its host plant (i.e. historical random dispersal from a highly diversified ancestral gene pool) and is probably the result of extensive gene flow from parasitoids associated with wild beans populations adjacent to crop fields. The study of evolutionary history integrating multitrophic levels has proved to be fruitful in detecting different evolutionary responses among members of the trophic module face to human and parasite interactions, but also points out the pertinence of analyzing ecological systems as a whole.

Le puceron du soya (Aphis glycines) est le ravageur le plus important de la culture du soya en Amérique du Nord. Quoi qu’efficaces, les pesticides permettent le contrôle des ravageurs que pour une courte période et nécessitent plusieurs applications au cours de la saison. De plus, ils sont dommageables pour l’environnement et la santé humaine. La lutte biologique se présente comme une alternative crédible pour le contrôle des populations d’A. glycines en Amérique du Nord. Trois parasitoïdes (Binodoxys communis, Aphidius colemani, Aphelinus certus) du puceron semblent être des candidats prometteurs. L’objectif de cette étude était d’examiner certains attributs biologiques de ces parasitoïdes au Québec. Dans le cas de B. communis et A. certus nous avons estimé leur synchronisme saisonnier ainsi que leur résistance au froid en laboratoire et en conditions naturelles. Dans le cas, d’A. colemani, nous avons évalué sa capacité à parasiter le puceron du soya et à se disperser dans un champ de soya. Nos résultats démontrent que la souche utilisée de B. communis a perdu sa capacité à entrer en diapause, probablement à cause de la longue période d’élevage en laboratoire qui a suivi son échantillonnage en Asie. Aphelinus certus démontre un potentiel intéressant puisqu’il possède un synchronisme saisonnier tant en automne qu’au printemps avec son hôte ainsi qu’un bon potentiel de survie hivernale au Québec. Quant à A. colemani, les essais suggèrent qu’il se disperse rapidement hors des champs sans attaquer de manière significative A. glycines. / The soybean aphid (Aphis glycines) has become the most important pest of soybean in North America. Despite their efficiency, insecticides do eliminate the pest only for short periods and several applications may be required during the growing season. Furthermore, they are detrimental for the environment and human health. Biological control appears as a promising alternative for the control of A. glycines populations in North America. Three parasitoid species (Binodoxys communis, Aphidius colemani, Aphelinus certus) have been identified as potential candidates. The objective of this study was to study some biological attributes of these parasitoids in Québec. For B. communis and A. certus we examined their seasonal activities and their cold hardiness in laboratory and natural conditions. For A. colemani, we evaluated its capacity to parasite the soybean aphid and to disperse in soybean fields. Our results revealed that the B. communis strain we used had lost its capacity to enter diapause, probably due to the long period of laboratory rearing following its sampling in Asia. Aphelinus certus showed an interesting potential because the species is synchronized with its host both in the fall and the spring and has the capacity to overwinter in Québec. For A. colemani, the essays suggest that it disperses rapidly out of the field without attacking significantly A. glycines.

This dissertation is concerned with effects dispersal and forest structure on forest insect population dynamics, and with identifying generating processes by comparing observed patterns to model predictions. In chapter 2, we investigated effects of changing forest landscape patterns on integro-difference models of host-parasitoid population dynamics. We demonstrated that removing habitat can increase herbivore density when herbivores don't disperse far, and parasitoids disperse further, due to differences in dispersal success between trophic levels. This is a novel potential explanation for why forest fragmentation increases the duration of forest tent caterpillar outbreaks. To better understand spatial model behaviour, we proposed a new local variation of the dispersal success approximation. The approximation successfully predicts effects of habitat loss and fragmentation on realistically complex landscapes, except when outbreak cycle amplitude is very large. Local dispersal success is useful in part because parameters can be estimated from widely available habitat data. In chapter 3, we investigated how well a discretized integro-difference model of mountain pine beetle population dynamics predicted the occurrence of new infestations in British Columbia. We found that a model with a large dispersal kernel, and high emigration from new, low severity infestations yielded the best predictions. However, we do not believe this to be convincing evidence that many beetles disperse from new, low severity infestations. Rather, we argued that differences in habitat quality, detection errors, and Moran effects can all confound dispersal patterns, making it difficult to infer dispersal parameters from observed infestation patterns. Nonetheless, predicting infestation risk is useful, and large kernels improve predictions. In chapter 4, we used generalized linear mixed models to characterize spatial and temporal variation in the propensity of jack pine trees to produce pollen cones, and account for confounding effects on the relationship between pollen cone production and previous defoliation by jack pine budworm. We found effects of stand age, and synchronous variation in pollen cone production among years. Accounting for background patterns in pollen cone production clarified that pollen cone production declines in with previous defoliation, as expected.