38th Annual Meeting of the Society for Invertebrate Pathology

August 7-11, 2005  Anchorage, Alaska, U.S.A
   

Transmission of Nosema fumiferanae in spruce budworm populations

Christina Campbell,1, Kees van Frankenhuyzen,2 and Sandy Smith 1.
1 Faculty of Forestry, University of Toronto, 33 Wilcocks Street, Toronto, ON M5S 3B3, Canada
2 Great Lakes Forestry Centre, Canadian Forest Service, Natural Resources Canada, P.O. Box 490, Sault Ste. Marie, ON P6A 5M7, Canada

A sublethal microsporidian, Nosema fumiferanae , may aid in driving spruce budworm population oscillations. Within a generation, horizontal transmission is the primary mode responsible for increasing Nosema prevalence. We infected laboratory larvae to parameterize the rate of transmission, and in the greenhouse we utilized vertically infected individuals to explore the ecology of horizontal transmission. In the laboratory, horizontal transmission was affected by temperature (F 1,37 = 7.49, p = 0.009) and was reduced at higher temperatures. Larval density did not affect horizontal transmission in the laboratory (F 2,24 = 2.61, p = 0.051) or in the greenhouse (F 4,18 = 2.52, p = 0.077). Horizontal transmission was significantly affected by initial infected density (F 4,18 = 7.66, p < 0.001). Experiments are in progress to further parameterize and study horizontal transmission. Additionally, in mid 2005, we will monitor a local budworm population for Nosema prevalence throughout the larval stage as an indicator for horizontal transmission. Vertical transmission of Nosema determines the initial density of infected larvae in the next generation. Infected adults enclose later than uninfected adults, which may play a role in passing infection to the next generation. We will examine the effect of Nosema spore density

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