Leptinotarsa decemlineata (Say) is the most important defoliating pest of potato Solanum tuberosum L., in North America and Europe.  Management of this pest relies heavily on chemical control and insecticide resistance is a persistent problem.  This phenomenon has increased the need for developing novel insecticides, resistance evaluation, and the development of alternative control strategies regarding this insect pest.  From 2010 to 2013, field and lab experiments were conducted to evaluate the efficacy of a novel insecticide tolfenpyrad on L. decemlineata.  In leaf-dip assays, tolfenpyrad was highly toxic to L. decemlineata with LC50 values of 0.013 and 0.164 g ai/L for larvae and adults, respectively.  Tolfenpyrad was also toxic to eggs with 0% hatching after being dipped in a field rate concentration.  In field efficacy trials, potato plots treated with tolfenpyrad at rates as low as 153 g ai/ha effectively controlled L. decemlineata. In 2012, populations of L. decemlineata were collected from the Eastern Shore of VA and subjected to toxicity assays to determine current susceptibility to permethrin and oxamyl.  The toxicity assays indicated an increase in toxicity to permethrin in L. decemlineata larvae (LC50 = 3.931 g ai/L) and an increase in toxicity to oxamyl in adult beetles (LC50 = 9.695 g ai/L) compared with LC50 values previously reported in 1990.  In 2012, populations of L. decemlineata from Cheriton, VA, New Church, VA, Painter, VA, and Plymouth, NC were also evaluated for enzyme activity after exposure to sub-lethal concentrations of permethrin, oxamyl, and tolfenpyrad.  Adult beetles were subjected to enzyme assays to measure the activity of cytochrome P450 mono-oxygenase (P450), glutathione-S-transferase (GST), general esterases, and protein content.  Results from the enzyme assays indicated significantly greater esterase activity in beetles from Painter, VA exposed to permethrin [±-naphthol (F= 11.66, df= 4, 20, P<0.0001) and "-naphthol (F= 11.86, df= 4, 20, P<0.0001)], oxamyl [±- naphthol (F= 10.64, df= 4, 20, P<0.0001) and "-naphthol (F= 6.94, df= 4, 20, P=0.0011)], tolfenpyrad [±- naphthol (F= 407.62, df= 1, 8, P<0.0001) and "- naphthol (F= 28.15, df= 1, 8, P= 0.0007)], and the untreated control [±- naphthol (F= 28.14, df= 3, 16, P<0.0001) and "- naphthol (F= 28.86; df= 3, 16, P<0.0001)] compared to most of the other populations tested.  GST activity was significantly greater in tolfenpyrad exposed beetles compared to the non-treated beetles from Painter VA (F= 17.66, df= 5, 24, P< 0.0001). Through laboratory assays and field experiments in potato, the efficacy of a new bio-pesticide derived from the bacterium Chromobacterium subtsugae was evaluated for the control of L. decemlineata.  Results from the laboratory assays showed L. decemlineata feeding was inhibited by the bio-pesticide derived from C. subtsugae.  However, field efficacy trials in 2010, 2011, and 2012, indicated no control of L. decemlineata. Methyl salicylate is an organic compound produced by potato and other plants in response to insect herbivory.  Abundance of predatory arthropods and L. decemlineata life stages were measured in plots treated with and without 5 g slow-release packets of methyl salicylate (95% methyl salicylate (Predalure")).  Methyl salicylate treatment had no impact on predator recruitment or cumulative mortality of L. decemlineata in potatoes. This research has provided us with a new tool for L. decemlineata management, as well as more information about resistance trends and alternative control strategies from which we can build on to reduce resistance development in L. decemlineata and ultimately formulate a stronger integrated pest management strategy for this insect pest. / Ph. D.

La vigne est une culture pérenne sensible à de nombreux bioagresseurs et sur laquelle il est nécessaire de réaliser de nombreux traitements pesticides, susceptibles de causer des problèmes environnementaux, de santé humaine et d’apparition de résistance au sein des populations de bioagresseurs. Aujourd’hui, il est indispensable de développer des stratégies nouvelles de lutte contre les bioagresseurs, plus raisonnées mais permettant de conserver une viticulture compétitive. L’utilisation de produits de biocontrôle semble, en ce sens, être une approche prometteuse permettant d’allier agriculture durable et intensive.Deux écoproduits généralistes à fort potentiel ont été identifiés, comme possédant des actions intéressantes sur les principales maladies cryptogamiques de la vigne. Le premier est un extrait naturel de plante, sans action fongicide directe mais capable de stimuler efficacement et de façon systémique les défenses de la plante. Le second, quant à lui, est un microorganisme qui possède une forte action antagoniste fongicide, mais aussi la capacité à stimuler les défenses de plante. Dans un premier temps, des études en conditions contrôlées ont mis en évidence l’efficacité des deux actifs pour inhiber le développement de diverses souches d’Erysiphe necator, Plasmopara viticola, Botrytis cinerea et Botryosphaeriaceae. En parallèle, des expérimentations au vignoble, ont confirmé le fort potentiel de ces produits de biocontrôle, avec des bonnes efficacités, particulièrement stable avec l’extrait naturel. Ces différentes études nous ont permis d’identifier et d’élaborer des stratégies d’utilisation pour ces deux produits de biocontrôle. / Grapevine is a perennial crop sensitive to many fungal pathogens that require numerous pesticide treatments. However, its uses lead to environmental, human health and fungicide resistance problems. Developing sustainable pest management strategies while keeping a good wine quality is of major importance. In this sense, the use of bio-pesticides products seems to be a promising approach to combine sustainable and intensive agriculture.Two generalist bio-pesticides of great potential have been preliminary identified, forits actions on major fungal diseases of grapevine. The first one is a natural plant extract, with no direct fungicide action but able to systemically stimulate plant defenses. The second one is a microorganism showing strong antagonist fungicide actions, and important ability to stimulate plant defenses. First, the studies conducted in controlled conditions have demonstrated the effectiveness of both products in the suppression of various isolates of Erysiphe necator, Plasmopara viticola, Botrytis cinerea and Botryosphaeriaceae. In parallel,the good efficiencies of these products have been confirmed during vineyard assays. This was especially well demonstrated for the natural extract. As a whole, these studies confirm thepotential of these two products as promising bio-pesticides, of which the strategy of application have been further defined.