Master of Science / Department of Entomology / James R. Nechols / Temperature has an important indirect impact on pest populations. Direct effects occur, but also may result from temperature-induced changes in plant quality, including the expression of host plant resistance traits. Therefore, I examined both indirect and direct effects of temperature on biotype 1 soybean aphids (SBA), Aphis glycines, on a Rag1-resistant soybean variety and compared the effects with a susceptible variety to gain a better understanding of how temperature impacts SBA. Four aphid responses were evaluated: preimaginal development, survival to adulthood, number of progeny produced, and adult longevity. In the first experiment, I grew soybean seedlings to the V-0 stage at 25°C and then conditioned them for 0, 3 or 5 days at 20° or 30°C before infesting with a single first instar SBA at each of the two experimental temperatures. Based on previous literature for SBA, I hypothesized that conditioning plants at the lower temperature would cause resistance to break down and that longer exposure would exacerbate the effect. Results showed that conditioning soybeans to 20°C significantly reduced SBA survival, and the effect on survival increased with longer conditioning. Conditioning plants to 30°C had no significant effect on SBA survival. However, estimated population growth decreased as conditioning time increased at 30°C and this effect was also observed at 20°C. Thus, plant resistance may have increased at both temperatures. The second experiment compared SBA responses, including population growth, at four temperatures (15, 20, 25, and 30⁰C) on a Rag1-resistant and susceptible soybean variety. I predicted that SBA fitness would be lower at all temperatures on resistant soybeans, but the magnitude of differences between cultivars would not be uniform across temperatures. Results indicated that both temperature (highest and lowest) and plant resistance detrimentally affected SBA fitness. There was also a significant interaction between the two variables with respect to SBA survival. Survival was lower and development rates were slower on the resistant cultivar. SBA required more degree-days to develop on resistant soybeans compared to the susceptible cultivar. This information will aid soybean producers in implementing a cost-efficient IPM strategy involving Rag1 resistant soybeans to combat SBA under a range of temperatures.

Soybean aphid, Aphis glycines Matsumura, is an important pest of North American soybean. This dissertation identifies and addresses knowledge gaps, and integrates existing knowledge regarding distribution and abundance of this species. Early summer soybean colonization patterns by A. glycines were examined relative to landscape parameters, including density of overwintering hosts (buckthorn). An information-theoretic model selection approach was used to determine which landscape parameters were most influential in the distribution of colonizing aphids. Though buckthorn abundance best explained aphid colonization and population density, a density-dependent effect was observed. When aphid populations were low, more aphids were found in the vicinity of buckthorn, when aphid populations were higher, more aphids were found farther from buckthorn. Suction trap captures of migrating populations of A. glycines from 2005-2009 from a suction trap network covering much of central North America were examined. A model selection approach was used to determine the environmental triggers of summer and fall aphid flights, and spatial analysis and modeled wind trajectories were used to examine patterns in the abundance of alates. Two alate activity peaks were observed in fall. In summer, formation of alates was a function of field infestation. A tritrophic population model was built using DYMEX, a mechanistic lifecycle based modeling software package. The model incorporated soybean, A. glycines, and three natural enemy species, interacting based on phenological, physiological and functional response data available in the literature. The model was validated using Ontario field data, and several simulations were performed and are discussed. An evaluation of proposed control strategies for efficacy and impact on natural enemies and the environment was conducted. Two novel concepts are presented: the natural enemy unit, a standardization of the impact of predator guild on prey populations by the number of prey an individual predator can eat, and the selectivity index, where the selectivity of a pesticide is a function of the change in ratio of natural enemy units to prey before and after treatment. The selectivity index was inversely correlated with the Environmental Impact Quotient (EIQ), a theoretical measure of impact, validating EIQ's field applicability. / Natural Sciences and Engineering Research Council of Canada; The Keefer family trust; the Mary Edmunds Williams trust, the family of Fred W. Presant, and the University of Guelph provided scholarship and fellowship funds. Research was funded by a grant to Rebecca Hallett and Art Schaafsma from the Agriculture and Agri-Food Canada Pest Management Centre’s Pesticide Risk Reduction Program.

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À partir d'un modèle existant de dynamique de populations de pucerons, nous avons développé une méthode permettant de quantifier la contribution de parasitoïdes à la réduction du maximum de densité de pucerons. La méthode a été validée, sur deux ans en champ de soya, en utilisant le modèle biologique composé du puceron du soya (Aphis glycines Matsumura) et de Aphelinus certus Jasnosh, son parasitoïde le plus abondant au nord-est de l'Amérique du Nord. La méthode a estimé que les densités naturelles de A. certus n'avait réduit les pics de densités de pucerons que de 1-6%. La cause de cette faible régulation est associée à un établissement tardif des populations de A. certus en champ de soya, mais les mécanismes sous-jacents restent inconnus. À cet effet, les proportions d'hyperparasitisme sur A. certus, avant le pic de densité de pucerons, étaient trop faible pour que l'hyperparasitisme puisse en être tenu responsable. Concernant la dynamique des populations de pucerons, nous avons proposé une re-paramétrisation du modèle mentionné précédemment afin de faciliter l'interprétation de ses paramètres lorsque la colonisation des champs par les pucerons n'était pas simultanée. Cette stratégie nous a permis d'établir que l'occurrence du pic de densité de puceron du soya est facilement prédictible de sa date de colonisation en champ. Nous recommandons l'utilisation de modèles afin de prédire les pics de densité de pucerons et d'utiliser la méthode d'estimation de l'impact afin d'incorporer des stratégies de relâchers augmentatifs de parasitoïdes aux programmes de lutte existants contre les pucerons. / Building upon an existing aphid population dynamics model, we develop a method to quantify the contribution of parasitoids in reducing the maximum aphid density. We validated the method, over a two years study in soybean fields, using the biological model made of the soybean aphid (Aphis glycines Matsumura) and Aphelinus certus Jasnosh, its most abundant parasitoid in north-eastern North America. The method estimated that natural populations of A. certus reduced peak soybean aphid densities by only 1-6%. The cause of this low regulation is associated to the late establishment of A. certus population in soybean field, although the underlying mechanisms remains unknown. Proportion hyperparasitism on A. certus, before peak soybean aphid densities, were too low for hyperparasitism to be accounted for the poor efficacy of A. certus in regulating the soybean aphid. Regarding aphid population dynamics, we proposed a re-parameterisation of the aforementioned model to facilitate the interpretation of its parameters when field colonization by aphids is not simultaneous. This allowed us to identify a high predictability in peak aphid densities from colonization time for the soybean aphid. We recommend using models to forecast peak aphid densities and to use the impact assessment method to incorporate augmentative parasitoid release strategies into aphid management programmes.

Alate morphs can benefit aphid populations by facilitating dispersal from deteriorating food sources and by escaping from natural enemies. Wing development, however, imposes constraints on fecundity. The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is an important economic pest in the U.S. and Canada. I conducted a series of laboratory and field experiments to determine the environmental factors inducing wing development in this species, and to determine the effects of asexual alate individual production on an A. glycines population under predation. My results reveal that wing induction in A. glycines occurs in response to interactions between crowding and decreased plant quality cues, and that alate aphid production benefits an aphid population under predation by increasing prevalence at a temporary cost to fecundity. My results contribute to the growing knowledge on the production of asexual alate aphids and provide insight into the biology of A. glycines as an agricultural pest. / May 2017

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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.

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.

No description available.