Although parasitoid wasps have shown promise as model systems for studying life history evolution, empirical studies of certain traits in these small insects have proven difficult. In this dissertation, two "black boxes" in the life histories of female parasitoids are examined: (1) oosorption, and (2) dispersal by flight.I first demonstrate that a short-lived species with high early reproductive investment (Eretmocerus eremicus) resorbs eggs, which runs counter to the notion that the time costs of oosorption are prohibitive to such wasps. Instead, it appears that the resorption mechanism in E. eremicus is capable of both decreasing costs and increasing nutritional benefits of oosorption relative to that of other parasitoid species. In addition, a literature review reveals four functional hypotheses for parasitoid oosorption: (1) age-related egg apoptosis, (2) conservation of ovarian capacity, and (3) nutrient allocation to either longevity or future oogenesis. As none of these can be rejected, I propose several avenues of future research: 1) refinement of physiological techniques to measure nutrient traffic into and out of eggs, 2) morphological phylogenetic studies of oosorption mechanisms, 3) development of lifetime nutrient budgets for parasitoids with different reproductive life histories, 4) examination of decay rates of oocytes with different yolk types, and 5) increased study of ovarian dynamics in pro-ovigenic parasitoids.Next, I describe results from a vertical flight chamber study designed to test hypotheses regarding the correlation between pre-oviposition dispersal and reproductive effort in parasitoid wasps. This experiment was conducted on 1-d-old female whitefly parasitoids from five species in two genera. The two Eretmocerus spp. showed a higher flight propensity than the three Encarsia spp. This may be, in part, due to a more time limited life history in the former. Within species, egg load did not correlate well with flight propensity for all species examined. Finally, among individuals of Er. eremicus, the relationship between effective flight distance and egg load appears to be context dependent, as data consistent with both positive and negative correlations were collected. Correlational changes between flight distance and egg load may be due to variation in biotic (female longevity) or abiotic (temperature, relative humidity) factors.

L'objectif principal de cette thèse est d'étudier comment la sélection naturelle façonne les traits d'histoire de vie et le comportement des animaux en fonction de l'environnement écologique dans lequel ils évoluent. Ce cadre théorique soulève des hypothèses spécifiques concernant les processus de reproduction, de dispersion et d'approvisionnement chez le parasitoïde Ibalia leucospoides. Les expériences d'écologie comportementale et d'écophysiologie menées sur des parasitoïdes femelles d' Ibalia leucospoides démontrent principalement que (1) la proportion d'oeufs matures que possède la femelle à l'émergence est élevée par rapport à sa fécondité potentielle : I. Leucospoides adopte une stratégie proovigénique ; (2) l'alimentation a un effet négligeable sur les femelles adultes : elle n'influence ni la maturation des oeufs, ni la survie, ni les capacités de vol ; (3) dans nos conditions expérimentales, la capacité de vol dépend des caractéristiques morphologiques du parasitoïde (taille et charge alaire) ; et (4) concernant la recherche d'hôtes, les femelles sont capables de discerner des différences dans la qualité des patchs d'hôtes à distance, sans les échantillonner. D'autre part, le temps d'exploitation d'un patch dépend des informations obtenues des patchs voisins. Le succès reproductif du parasitoïde proovigénique Ibalia leucospoides, n'est pas limité par le manque de nourriture chez l'adulte. La stratégie d'allocation des ressources entre les différentes fonctions biologiques, ainsi que le comportement d'approvisionnement adopté par cette espèce de parasitoïde pourraient vraisemblablement être une réponse aux caractéristiques de l'habitat, telle que la distribution fortement agrégée des Sirex noctilio, l'hôte, ainsi que la disponibilité des ressources (i.e. hôtes et nourriture) / The central aim of this thesis is to explore how natural selection shapes life history traits and behaviuors according to the ecological environment in which an animal exists. This overall framework leads to specific hypotheses concerning the reproductive, dispersal and foraging processes in the parasitoid Ibalia leucospoides. The experiments in behavioural ecology and eco-physiology in female parasitoids of Ibalia leucospoides show as main results, that (1) the proportion of the potential lifetime eggs complement that is mature at female emergence is high; (2) low dependency on adult female feeding, not only for egg maturation but also for survival and flight; (3) under our experimental conditions flight capacity depends on the morphological characteristics of the parasitoid (size and wing loading); and (4) regarding host foraging, females accurately assess differences in host patch quality from a distance without the need of displaying a sampling process; in addition that patch exploitation times depend on the information obtained from the surrounding patches. The reproductive success of I. leucospoides, a proovigenic parasitoid, is not constrained by adult food deprivation. Both the resource allocation strategy toward the different biological functions and the foraging behaviour adopted by this parasitoid species may well be in respond to habitat characteristics, such as a strongly aggregated distribution of Sirex noctilio, the host, as well as to the resources availability (i.e. host and food)