Prevalence of Nosema sp. (Microsporidia: Nosematidae) during an outbreak of the jack pine budworm in Ontario |
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Authors: | van Frankenhuyzen Kees Ryall Krista Liu Yuehong Meating Joe Bolan Paul Scarr Taylor |
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Institution: | aGreat Lakes Forestry Centre, Canadian Forest Service, Natural Resources Canada, 1219 Queen Street East, Sault Ste. Marie, Ontario, Canada P6A 2E5;bBioforest Technologies Inc., 105 Bruce Street, Sault Ste. Marie, Ontario, Canada P6A 2X6;cForest Health and Silviculture Section, Ontario Ministry of Natural Resources, 70 Foster Drive, Sault Ste. Marie, Ontario, Canada P6A 6V2 |
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Abstract: | Microsporidia are believed to play little or no role in outbreaks of the jack pine budworm, Choristoneura pinuspinus Freeman (Lepidoptrera: Tortricidae), because the short duration (2–4 years) of those outbreaks may not permit significant build-up of the pathogen. We conducted the first survey of Nosema sp. (Microsporidia: Nosematidae) over the course of a recent jack pine budworm outbreak in Ontario. Between 2004 and 2010 the outbreak defoliated a cumulative total of 1.78 million ha. Microscopic examination of ∼15,000 overwintering larvae collected over 6 years in sites with densities of 3 larvae per branch or more revealed widespread occurrence of Nosema at generally high infection intensities. The pathogen was present in 69.5% of the 518 plots that were monitored. Prevalence of infection was generally low (below 40% in 84% of plots with infected larvae) but reached high levels (80–95%) locally and increased rapidly in most infestations within 1–2 years of onset. We hypothesize that the habit of early-instar larvae to feed on developing male flowers (pollen cones) after spring emergence is critical in allowing rapid build-up of Nosema by increasing efficiency of horizontal transmission (higher density of both infected larvae and egested spores). Nosema infection may contribute to the complexity of jack pine budworm outbreak patterns by affecting egg recruitment and early-instar survival at the stand level in concert with known effects of budworm-induced reductions in pollen cone production on those processes. |
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Keywords: | Choristoneura pinus pinus Jack pine budworm outbreak Microsporidia Nosema Horizontal transmission Epizootiology |
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