Thesis (Ph. D.)--University of Adelaide, Dept. of Crop Protection, 1996. / Includes bibliographical references (leaves 221-240).

Thesis (M. Sc.)--University of Canterbury, 2002. / Typescript (photocopy). Includes bibliographical references (leaves 71-98). Also available via the World Wide Web.

Universiẗat, Diss.--Kiel, 2001. / Zsfassung in dt. u. engl. Sprache.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Universiẗat, Diss., 2000--Kiel.

En milieu naturel, les organismes doivent s’adapter à un environnement lumineux changeant (alternance jour/nuit, couverture nuageuse, habitat, saison, etc.). L'utilisation croissante de longueurs d'ondes spécifiques impliquant des diodes électroluminescentes (DELs) en serres permet de surmonter le manque de lumière pendant les mois d'hiver, en aidant la photosynthèse ou la croissance végétative des cultures. Cependant, la modification de l'environnement lumineux ainsi que de la photopériode peut également modifier directement ou indirectement l'activité des insectes utiles et des insectes nuisibles qui dépendent des plantes. Dans mon étude, nous avons étudié comment une guêpe parasitoïde fait face aux variations du spectre d'éclairement et à quel point la vision des couleurs est importante dans la localisation et la reconnaissance de son hôte. Notre modèle d’étude s’est porté sur la guêpe parasitoïde Aphidius ervi qui attaque principalement le puceron du pois Acyrthosiphon pisum. Les pucerons du pois présentent un polymorphisme de couleur et apparaissent au sein d’une même population sous la forme de morphes roses et de morphes verts. En utilisant un montage basé sur des DELs de 5 longueurs d’ondes différentes (361, 450, 500-600, 626 and 660 nm), nous avons créé différents spectres lumineux artificiels que les parasitoïdes et leurs hôtes peuvent rencontrer dans l’environnement naturel tels que l’ombre des feuilles ou le soleil direct. Ce design nous a permis d’étudier le comportement des insectes face à un environnement lumineux changeant et totalement contrôlable en intensité lumineuse et en composition spectrale, dans un contexte d'activité locomotrice et de parasitisme. Dans l’ensemble, les résultats suggèrent que la probabilité que les pucerons se déplacent dépendait de l’interaction entre l’environnement lumineux, le stade de développement et la variation clonale. Nous avons montré que la probabilité que les parasitoïdes soient actifs diminuait avec l’augmentation des longueurs d’onde. Les mâles étaient plus actifs que les femelles sous toutes les conditions lumineuses monochromatiques testées. Bien que la quantité de lumière réfléchie des morphes roses fût d’environ la moitié de celle des morphes verts dans les composantes cyanvert, nous avons constaté que les deux couleurs d’hôtes ont été reconnues et attaquées dans toutes les conditions d'éclairage testées, même la lumière rouge (660 nm). Enfin, en appliquant 4 ratios de DELs rouges (R): bleues (B) utilisées pour allonger la photopériode à l'intérieur d'une chambre de croissance, nous avons montré que l’allongement de la photophase (de 8h à 16 h de lumière/jour) augmentait l'activité parasitaire quotidienne de la guêpe ainsi que son comportement en matière de ponte. Enfin, les adultes parasitoïdes nouvellement émergés étaient composés de 80 % de mâles en lumière 100R: 0B contre 50 % sous le ratio 25R: 75B. Cette étude indique qu'A. ervi reste un bon agent de lutte biologique lorsque l'environnement lumineux est modifié. Elle est aussi la première à montrer que le ratio de lumière R: B a un impact sur l’allocation des sexes chez ce parasitoïde. Nous pensons que l’utilisation de la lumière rouge seule pour prolonger la photophase peut avoir un effet négatif sur la dynamique des populations de ces parasitoïdes en raison de son impact défavorable sur le sex-ratio en favorisant les mâles, et donc un effet négatif sur le contrôle des populations de pucerons en milieu confiné. / In nature, organisms must adapt to a changing light environment (day / night alternation, cloud cover, habitat, season, etc.). The increasing use of specific wavelengths involving light emitting diodes (LEDs) in greenhouses overcomes the lack of light during winter months, helping photosynthesis or vegetative growth of crops. However, changing light environment as well as photoperiod can also directly or indirectly modify the activity of beneficial insects and plant-related pests. In my study, we investigated how a parasitoid wasp deals with variations in the light environment and how important color vision is in locating and recognizing its host. Our study model focused on the parasitoid wasp Aphidius ervi which mainly attacks the pea aphid Acyrthosiphon pisum. Pea aphids have a color polymorphism and appear within a same population under pink morphs and green morphs. Using a design based on LEDs of 5 different wavelengths (361, 450, 500-600, 626 and 660 nm), we have created different artificial light spectra that parasitoids and their hosts can encounter in natural environment such as leaf-shade or direct sunlight. This design allowed us to study the behavior of insects in a changing light environment that is totally controllable in light intensity and spectral composition, in a context of locomotor activity and parasitism. Overall, the results suggest that the probability of aphids walking depended on the interaction between the light environment, the stage of development, and clonal variation. We have shown that the probability of parasitoids walking decreased with increasing wavelengths, and that males were more active than females under all monochromatic light conditions tested. Although the amount of light reflected from the pink morphs was about half that of the green morphs in the cyan-green components, we found that both host colors were recognized and attacked under all light conditions tested, even red light (660 nm). Finally, by applying 4 ratios of red (R): blue (B) LEDs used to extend the photoperiod inside a growth chamber, we have shown that the photophase elongation (from 8h to 16h of light/day) increased the daily parasitic activity of the wasp and its oviposition behavior. Finally, the newly emerged parasitoid adults were composed of 80% males in light 100R: 0B against 50% under the ratio 25R: 75B. This study indicates that A. ervi remains a good biological control agent under different light environments. This study is also the first to show that the R: B light ratio has an impact on the decision-making of females regarding the sex of their offspring. We believe that the use of red light alone to extend the photophase may have a negative effect on the population dynamics of these parasitoids because of its adverse impact on sex ratio by favoring males, and thus a negative effect on control of aphid populations in confined environment.

Investigations were carried out on the seasonal changes of aphids, particularly Myzus persicae (Sulz.), on hrussels sprouts and the importance of their natural enemies, from autumn 1968 to spring 1971 in the area around Edinburgh. M. persicae overwintered anholocyclically on weeds, particularly on dock plants, hut rarely on brassica crops. Plants in glasshouses also provided overwintering sites for M. persicae and Macrosiphum euphorbiae (Thomas). These aphids started gradually to infest the brussels sprout plants during the end of June in a constant but irregular movement. Both M. persicae and M.euphorbiae have no fixed patterns of population changes throughout the field nor from year to year. During early July the initially low densities of M. persicae and M. euphorbiae populations increased fast. By early August parasitism and predation increased; condensation of water droplets on the aphids also appeared in August and drowned some of them. Subsequently these mortality factors caused a sharp decline of the first peak of M. persicae abundance, and complete disappearance of H. euphorbiae from the field by mid-September. Favourable weather and reduced activities of natural enemies caused another peak of M. persicae to be reached in September. A slight drop in abundance occurred again, due mainly to parasitism; the third and last peak of a season appeared during late October and early November. The fall of this peak was attributed to the cold weather which reduced the rate of reproduction and hastened the abscission of bottom leaves which carried the aphid population. Eighteen species in eight genera of aphid parasites and at least eight species in five genera of hyperparasites were recorded. All the eleven species of primary parasites and five genera containing at least eight species of hyperparasites noted as parasites of M. persioae; and fifteen species of primary parasites and five genera of at least eight species of the hyperparasites listed tinder M. euphorbias were first records of any such parasites in Scotland. The M. persicae records as aphid host of seven species of primary parasites and two genera of at least three species of hyperparasites; and M. euphorbiae also as an aphid host of seven species of primary parasites and two genera of at least four species of hyperparasites were new records in Britain. Three and four species of primary parasites listed respectively under M, persicae and M. euphorbiae as aphid host were found to he new records in the general literature. Praon volucre (Hal.) was the dominant species of the primary parasites followed by Diaeretiella rapae Mcintosh and Aphidius picipes (Hees) which were about half and one third as numerous as the dominant species. Asaphes vulgaris Walker was the dominant species of the hyperparasites with cynipids about equally abundant. Some aspects of the bionomics of hyperparasites and primary parasites, particularly P. volucre, were given. Factors which limited the effectiveness of the parasites, particularly P. volucre, included 1. the fast developmental rate and the lower threshold of the aphid host (M, persicae) as compared to that of thep parasite (P. volucre). 2. hyperparasitism; - in 1969 and 1970 aphids on brussels sprouts were hyperparasitised respectively to the extent of 39.4% and 46.9% 3. harvesting of brassica crops during autumn which destroyed some of the aphid mummies and the aphid populations which could be parasitised to increase the numbers of the overwintering mummies. 4. overwintering of the parasites which started during late summer and early autumn while the aphid hosts were reproducing.

Bibliography: leaves 221-240. This thesis deals with the introduction of "Aphidius rosae" as a classical biological control agent into South-Eastern Australia. Appropriate host specificity tests are carried out. Laboratory experiments are also completed to gain a better understanding of the interactions between host and parasitoid in the field. The study aims to monitor the performance of the control agent in the Adelaide environment for the first two years after initial release. It is also planned to invent an experimental field technique to estimate the impact of the control agent on rose aphid populations.

Bibliography: leaves 221-240. / viii, 240, [13] leaves : ill. (some col.), maps ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis deals with the introduction of "Aphidius rosae" as a classical biological control agent into South-Eastern Australia. Appropriate host specificity tests are carried out. Laboratory experiments are also completed to gain a better understanding of the interactions between host and parasitoid in the field. The study aims to monitor the performance of the control agent in the Adelaide environment for the first two years after initial release. It is also planned to invent an experimental field technique to estimate the impact of the control agent on rose aphid populations. / Thesis (Ph.D.)--University of Adelaide, Dept. of Crop Protection, 1997

Thèse ( Ph.D.)--Université Laval, 2004. / Titre de l'écran-titre (visionné le 29 novembre 2004). Bibliogr.