Thèse (Ph.D.)--Université Laval, 2003. / Titre de l'écran-titre (visionné le 22 mars 2004). Bibliogr.

Chez les espèces d’insectes dont le développement larvaire nécessite plusieurs hôtes, la survie larvaire peut être dépendante à la fois du comportement d’oviposition des femelles et du comportement de recherche des larves. La présente thèse porte sur l'étude de ces deux comportements et leurs possibles impacts sur la performance larvaire de la pyrale de la canneberge, Acrobasis vaccinii (Lepidoptera: Pyralidae), une espèce dont chaque larve a besoin de plusieurs fruits de canneberge, Vaccinium oxycoccos (Ericacae), pour compléter son développement. Dans un premier temps, j’ai démontré que les femelles en laboratoire pondent significativement plus souvent sur les plus gros fruits disponibles; la taille des larves sortant du premier fruit choisi par la femelle étant proportionnelle à la taille de ce fruit. Cependant, sur le terrain, cette préférence n’a pas été observée et mon étude met en évidence que la période d’oviposition survient tôt dans la saison, dès l’apparition des premiers fruits; ceci impliquant une faible variabilité dans la taille des sites de ponte disponibles. Cette étude démontre également une distribution hétérogène des fruits de canneberge en nature et une variabilité importante dans la production annuelle de fruits entre mes deux années d’étude. Le fait que les fruits puissent être rares certaines années serait une raison conduisant les femelles à accepter les fruits de plus faible qualité (fruits de petite taille). Ainsi, cette étude démontre une plasticité dans le comportement d’oviposition chez A. vaccinii, les femelles ne devenant sélectives que lorsque les conditions sont favorables (telles que celles en laboratoire). Dans un deuxième temps, mon étude du comportement d'alimentation des larves a démontré l'induction du rougissement des fruits après l'attaque par une larve. Cette modification peut constituer un indice dissuadant les conspécifiques de se diriger vers des fruits déjà occupés et représente un moyen de réduire la compétition intraspécifique larvaire. Cette étude démontre également la capacité des larves à tenir compte de la taille des fruits et de la distance à parcourir pour atteindre les hôtes. Les larves A. vaccinii présentent une plasticité comportementale en accordant une importance variable à chacun de ces différents facteurs (taille du fruit, couleur du fruit et distance entre les fruits) selon le contexte, ceci leur permettant de maximiser la recherche de nourriture tout en réduisant les risques de compétition intraspécifique et de prédation. / In insect species whose larvae need several hosts to complete their development, larval survival is usually dependent on both the choice of oviposition sites by females and the food searching behaviour of larvae. In this thesis, I studied oviposition behaviour and larval foraging behaviour and their possible impacts on larval fitness in the cranberry fruitworm, Acrobasis vaccinii (Lepidoptera: Pyralidae), a species in which each larva must feed on several fruits of the cranberry, Vaccinium oxycoccos (Ericacae), to complete its development. Firstly, I demonstrated that females, under laboratory conditions, exhibit a significant preference for the largest fruit available when choosing oviposition sites; larvae leaving these maternally selected large fruits were significantly larger than those larvae leaving smaller fruits. In the field, however, this preference based on fruit size was not observed. This lack of preference in nature may be due, in part, to the fact that the oviposition period of A. vaccinii is relatively early during the summer when cranberry fruits are still small and when there is little variation in the size of fruits available. I also found a heterogeneous distribution of hosts in patches of varying fruit densities, and a large variability in fruit production between the two years of my study. The fact that, in any given year, hosts may be rare may be a reason why females accept relatively low-quality hosts (i.e., relatively small fruits). Thus, this study demonstrates a behavioural plasticity in A. vaccinii, females selecting largest fruits only when environmental conditions are good (such as in our laboratory conditions). A second study on larval feeding behaviour demonstrated that green cranberry fruit become red following attacks by A. vaccinii larvae. This host modification (fruit colour) may be a cue used by conspecific larvae to avoid already infested fruits, thus reducing the risk of intraspecific competition. I also showed that A. vaccinii larvae are able to take into account two other factors - fruit size and distance between hosts - in their choice of fruit. Larvae of A. vaccinii show behavioural plasticity when choosing fruit in that they accord a different degree of importance to each factor (fruit size, fruit colour and distance between fruit) depending on the context. This plasticity allows the larvae to maximise foraging efficiency while minimising intraspecific competition and predation risk.

The species Dendranthema indicum, a type of garden chrysanthemum, has the following characteristics: perennial, low height, rustic, and produces a great amount of inflorescences. The commercial production of this species in vase is done in a na empirically way. The objective of this study was to determine the cultivar cycle, size of vase, number of cuttings, environment adaptability, the topiary technique and qualitative standards of commercialization for two cultivars, Papiro and Veria Dark. The experiment was performed in three different sizes of vases (numbers 11, 15 and 20), using only one plant per vase, which received 4, 6 and 7 cuttings, respectively. Increasing the vase size increased the plant size, and the number of inflorescences but reduced the diameter of these. The environment conditions at Santa Maria, RS, are not limitating to production of vases with plants with topiary technique. However, the cycle of cultivar Veria Dark was increased in one week. It is possible to obtain plants with good quality cultivating them in vases number 15 or 20, with a minimum of five cuttings number. It was not possible to obtain plants of cultivar Veria Dark, with quality for commercialization using vase 11. The ratio of height of plant/height of vase and closing were the parameters that better evaluated the quality of the vases / A espécie Dendranthema indicum Tzvelev., é um crisântemo de jardim, cujas plantas são perenes, porte baixo, rústicas e produzem grande quantidade de inflorescências. A produção comercial desta espécie em vaso vem sendo feita de modo fortuito. Este trabalho teve como objetivos determinar o ciclo de cultivares, o tamanho de vaso, o número de despontes, a adaptabilidade ao ambiente local e à topiaria e propor padrões qualitativos de comercialização para as cultivares Papiro e Veria Dark. Essas foram conduzidas em três diferentes tamanhos de vasos, números 11, 15 e 20, utilizando uma planta por vaso, que receberam 4, 6 e 7 despontes respectivamente. O aumento do tamanho do vaso aumenta o tamanho da planta e o número de inflorescências mas diminui o diâmetro dessas. As condições ambientais de Santa Maria, RS, não são limitantes à produção de vasos com planta conduzida sob a técnica de topiaria, no entanto, o ciclo da cultivar Veria Dark aumentou uma semana. É possível obter-se plantas de boa qualidade cultivando-se em vasos número 15 ou 20, com no mínimo cinco despontes. Para a cultivar Veria Dark vaso 11 não foi possível obter plantas com qualidade para comercialização. As relações de altura de planta/altura de vaso e fechamento foram os parâmetros que melhor avaliaram a qualidade dos vasos