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PATHOGENICITY OF NOSEMA FUMIFERANAE (THOMSON) (MICROSPORIDA) IN SPRUCE BUDWORM, CHORISTONEURA FUMIFERANA (CLEMENS), AND IMPLICATIONS OF DIAPAUSE CONDITIONS1

Published online by Cambridge University Press:  31 May 2012

Leah S. Bauer  and
Gerald L. Nordin
Leah S. Bauer
Affiliation:
North Central Forest Experiment Station, USDA Forest Service, 1407 South Harrison Road, East Lansing, Michigan, USA48823
Gerald L. Nordin
Affiliation:
Department of Entomology, University of Kentucky, Lexington, Kentucky, USA40546
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Abstract

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A standardized bioassay procedure was used to determine median lethal doses (LD50) of the microsporidium, Nosema fumiferanae (Thom.), on newly molted fourth- and fifth-instar eastern spruce budworm larvae (Choristoneura fumiferana (Clem.)). The LD50 for fifth-instar larva was 1.23 × 106 ± 2.82 × 105 spores. The fourth-instar LD50 was 2.23 × 104 ± 4.30 × 103 spores per larva for populations experiencing prolonged post-diapause cold storage or an elevated temperature during diapause and 2.00 × 105 ± 6.66 × 104 spores per larva for populations not experiencing stressful conditions during and after diapause. Median lethal times (LT50) ranged from 6 to 19 days, depending on instar and dose level. Sublethal responses of fourth- and fifth-instar larvae inoculated with serial dilutions of spores were estimated by significant linear models. These regressions were negative for pupal weight and adult longevity and positive for development time (duration of instar VI). Inoculations of newly molted sixth-instar larvae produced similar models, although development time was not significantly affected. Insects reared following stress during and after diapause had consistently longer developmental times. The importance of prolonged developmental time on disease expression and insect susceptibility is discussed.

Résumé

On a utilisé une méthode standard pour déterminer les doses létales médianes (LD50) de la microsporidie Nosema fumiferanae (Thom.) pour des larves nouvellement muées des stades quatre et cinq de la tordeuse des bourgeons de l’épinette, Choristoneura fumiferana (Clem.). La dose létale médiane (LD50) pour les larves de cinquième stade était 1,23 × 106 ± 2,82 × 105 spores. La LD50 pour les larves de quatrième stade était 2,23 × 104 ± 4,30 × 103 spores par larve chez des populations ayant subi un refroidissement post-diapause prolongé ou une élévation de température durant la diapause, et 2,00 × 105 ± 6,66 × 104 spores par larve n’ayant pas subi de conditions stressantes durant, ou après la diapause. Les délais de mortalité (LT50) ont varié de 6 à 19 jours selon le stade et la dose. On a caractérisé les réactions sub-létales des larves des stades quatre et cinq inoculées avec des dilutions en série des spores par des modèles de régression linéaire significatifs. Ces régressions étaient négatives dans le cas du poids des pupes ou de la longévité adulte, et positives pour la durée de développement (au stade VI). L’inoculation de larves de stade six nouvellement muées a révélé des modèles similaires, bien que la durée du développement n’ait pas été affectée. Les insectes ayant subi un stress durant ou après la diapause montraient invariablement un prolongement du développement. On discute de l’importance du prolongement du développement pour l’expression de la maladie et la susceptibilité de l’insecte.

Type
Articles
Information
The Canadian Entomologist , Volume 120 , Issue 3 , March 1988 , pp. 221 - 229
Copyright
Copyright © Entomological Society of Canada 1988

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