During a two years study (1993-1994) in southwestern Quebec, Artogeia rapae and Plutella xylostella were found to be the most important lepidopterous pests of cruciferous crops, followed by Trichoplusia ni and four minor species. The relationship between plant sampling and the use of degree-days, pheromone traps (P. xylostella) or butterflies counts (A. rapae) was assessed for A. rapae and P. xylostella. Three generations of A. rapae were observed annually, with a duration of 319.7 degree-days above $ rm 10 sp circ C (DD sb{10}),$ while P. xylostella had three to four generations with a duration of 277.7 $ rm DD sb{10}.$ Captures of P. xylostella were not linked to the level of infestations. By the end of summer, A. rapae was the most abundant species, especially on broccoli, while P. xylostella was often abundant early in the season. The complex of lepidopterous pests' natural enemies was identified, and the data were analyzed using an illustrated parasitoid web. Fourteen parasitoid and three hyperparasitoid species (12 Hymenoptera, 2 Diptera) were identified. The most important parasitoid, Cotesia rubecula, is a larval parasitoid of A. rapae that is newly established in Quebec. Overall, parasitism of lepidopterous eggs is almost not existent, whereas parasitism and infection of larvae and pupae by pathogens are important, but not significant to reduce butterfly populations. In order to evaluate the potential of oophagous parasitoids, the parasitism of up to 42 species/strains of Trichogramma was studied with different development stages of P. xylostella, A. rapae and T. ni eggs. Generally, Trichogramma females attacked preferably young eggs of a given host species. Females modified the number of offspring according to host size and host age, as fewer offspring emerged from the smallest or the oldest hosts. Host age had no impact on sex allocation. (Abstract shortened by UMI.)
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.27327 |
| Date | January 1997 |
| Creators | Godin, Claude, 1970- |
| Contributors | Boivin, Guy (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Natural Resource Sciences.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001572132, proquestno: MQ29702, Theses scanned by UMI/ProQuest. |
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