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  • S.M. Smith (a1), D.R. Wallace (a2), G. Howse (a2) and J. Meating (a2)


The ability of the egg parasitoid, Trichogramma minutum Riley, to suppress outbreak populations of the spruce budworm, Choristoneura fumiferana (Clemens), was studied annually near Hearst, Ont., from 1982 through 1986. Timing of broadcast parasitoid-releases was linked to spruce budworm moth emergence and oviposition. These phenological relationships were predicted from a regression based on larval development at least 2 weeks before expected emergence; this allowed sufficient time to regulate (program) parasitoid emergence during mass-rearing. Emergence of caged spruce budworm adults was used to monitor moth eclosion in the field. Pheromone traps provided daily information on the activity of male moths and helped to synchronize the parasitoid releases with spruce budworm oviposition. Information on parasitoid activity was obtained from sentinel (laboratory-reared) and naturally occurring spruce budworm egg masses. A curvilinear relationship between the rate of parasitoid release and parasitism of sentinel egg masses was developed. Two parasitoid releases, 1 week apart, early in the oviposition period of spruce budworm, significantly increased parasitism of host eggs by 14–83% and reduced larval populations correspondingly from 42 to 82%. Single releases were less effective and increased parasitism by 0.3–52% (single ground release, 1986). Two parasitoid releases, combined with a spring application of Bacillus thuringiensis Berliner to larval populations, was the most effective strategy and resulted in 83% egg parasitism and 93% larval reduction. Release rates greater than 12–16 × 106 ♀ ♀ T. minutum per hectare were not warranted based on impact and costs. The effects of release timing, weather, host density, and parasitoid quality on the future successful use of T. minutum are discussed.

La capacité du parasitoïde de l'oeuf, Trichogramma minutum Riley, à supprimer les populations éruptives de la tordeuse des bourgeons de l'épinette, Choristoneura fumiferana (Clemens), a été étudiée annuellement, près de Hearst, Ont., à partir de l'année 1982 jusqu'à l'année 1986 comprise. Le réglage de relâchements de parasitoïdes à la volée a été lié à l'éclosion et la ponte de la tordeuse. Ces rapports phénologiques ont été prédits d'une régression basée sur le développement larvaire au moins 2 semaines avant l'éclosion attendue; ceci a donné du temps suffisant à régler (à mettre en marche) l'éclosion des adultes de la tordeuse dans les cages a été utilisée pour contrôler l'éclosion du Lépidoptère dans les champs. Les pièges de phéromones ont fourni des renseignements journaliers concernant l'activité des mâles adultes et ont aidé à synchroniser les relâchements de parasitoïdes avec la ponte de la tordeuse. Les renseignements concernant l'activité des parasitoïdes ont été obtenus des masses d'oeufs de référence (élevages du laboratoire) et de celles qui se présentaient en nature. Un rapport curviligne entre la vitesse de relâchement du parasitoïde et le parasitisme des masses d'oeufs de référence a été développé. Deux relâchements de parasitoïdes, séparés de 1 semaine, au début de la ponte de la tordeuse, ont augmenté significativement le parasitisme des oeufs de l'hôte de 14–83% et ont réduit les populations larvaires également de 42–82%. Les relâchements simples ont été moins efficaces et ont augmenté le parasitisme de 0,3–52% (relâchements terrestres simples en 1986). Deux relâchements de parasitoïdes, joints à un traitement printanier des populations larvaires avec Bacillus thuringiensis Berliner, se sont montrés le stratège le plus efficace et ont eu comme résultat un parasitisme d'oeufs de 83% et une réduction de larves de 93%. Les taux de relâchement plus extensifs que de 12–16 × 106 ♀ ♀ T. minutum par hectare n'ont pas été justifiés d'une base d'effet et de frais. Ont été discutés les effets du relâchement, du réglage, du temps, de la densité de l'hôte et de la qualité du parasitoïde sur l'utilisation réussie à l'avenir de T. minutum.



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  • S.M. Smith (a1), D.R. Wallace (a2), G. Howse (a2) and J. Meating (a2)


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