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Virulence of the entomopathogenic fungus Lecanicillium (Deuteromycota: Hyphomycetes) to Pissodes strobi (Coleoptera: Curculionidae)

Published online by Cambridge University Press:  02 April 2012

Harry H. Kope ,
René I. Alfaro  and
Robert Lavallée
Harry H. Kope*
Affiliation:
Pacific Forestry Centre, Canadian Forest Service, Victoria, British Columbia, Canada V8Z 1M5
René I. Alfaro
Affiliation:
Pacific Forestry Centre, Canadian Forest Service, Victoria, British Columbia, Canada V8Z 1M5
Robert Lavallée
Affiliation:
Centre de foresterie des Laurentides, Service canadien des forêts, Sainte-Foy, Québec, Canada G1V 4C7
*
1 Corresponding author (e-mail: hkope@pfc.cfs.nrcan.gc.ca).
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Abstract

The widely occurring fungal genus Lecanicillium Zare & W. Gams (formerly Verticillium) includes species that are pathogenic to insects. We collected 27 Lecanicillium isolates from soil and from dead adult Pissodes strobi (Peck) in British Columbia, Canada, and assessed their virulence against this host. Eighteen isolates were identified as L. longisporum (Petch) Zare & W. Gams and six as L. muscarium (Petch) Zare & W. Gams, while three isolates could not be identified to the species level. We assayed a subset of these isolates (14 L. longisporum, 3 L. muscarium, and 1 Lecanicillium sp.) as well as the fungal component of the commercial products Mycotal® (L. muscarium) and Vertalec® (L. longisporum) and a herbarium isolate (Lecanicillium sp.). When adult weevils were inoculated with a conidial suspension (1 × 107 conidia/mL), mycosis-related mortality at the end of a 17-day incubation period varied between 20% and 100%, depending on the isolate tested. Eight of the isolates killed >75% of weevils: a Lecanicillium sp. isolate, PFC19, which displayed the lowest LT50 value; five indigenous L. longisporum isolates; and both commercial products. In a goodness-of-fit test comparing isolate virulence among species, the unidentified PFC19 isolate was found to be more effective than either L. longisporum or L. muscarium, while L. longisporum caused somewhat greater mortality than L. muscarium. In a similar analysis, isolates extracted from soils tended to be more effective than those obtained from cadavers. Horizontal transmission to live P. strobi was observed using different isolates of Lecanicillium species. Notwithstanding the variability in virulence, the indigenous Lecanicillium species that we isolated and assayed are confirmed as pathogenic to P. strobi in British Columbia.

Résumé

Le genre de champignons Lecanicillium Zare & W. Gams (précédemment Verticillium) à large répartition géographique contient des espèces pathogènes pour les insectes. Nous avons recueilli 27 isolats de Lecanicillium dans le sol et sur des cadavres d'adultes de Pissodes strobi (Peck) en Colombie-Britannique, Canada, et nous avons évalué leur virulence vis-à-vis cet hôte. Dix-huit des isolats ont été identifiés comme L. longisporum (Petch) Zare & W. Gams et six comme L. muscarium (Petch) Zare & W. Gams, alors que trois autres n'ont pu être identifiés à l'espèce. Nous avons évalué un sous-ensemble de ces isolats (14 L. longisporum, 3 L. muscarium et 1 Lecanicillium sp.), de même que la composante fongique des produits commerciaux Mycotal® (L. muscarium) et Vertalec® (L. longisporum) et un isolat d'herbier (Lecanicillium sp.). Après une inoculation avec une suspension de conidies (1 × 107 condidies/mL), les charançons adultes subissent après une période d'incubation de 17 jours une mortalité due à la mycose qui varie de 20 % à 100 % selon l'isolat utilisé. Huit des isolats tuent >75 % des charançons, dont un isolat de Lecanicillium sp. (PFC19) qui possède le LT50 le plus bas, cinq isolats indigènes de L. longisporum et les deux produits commerciaux. Un test d'ajustement qui compare la virulence de l'isolat en fonction de l'espèce montre que l'isolat non indentifié PFC19 est plus efficace que L. longisporum et que L. muscarium et que L. longisporum cause un mortalité un peu plus élevée que L. muscarium. Une analyse similaire montre que les isolats extraits des sols ont tendance à être plus efficaces que ceux récoltés sur les cadavres. Nous avons observé une transmission horizontale chez des P. strobi vivants à l'aide de différents isolats de Lecanicillium. Malgré la variabilité de leur virulence, les espèces indigènes de Lecanicillium que nous avons récoltées et évaluées se sont avérées pathogènes pour P. strobi en Colombie-Britannique.

[Traduit par la Rédaction]

Type
Articles
Information
The Canadian Entomologist , Volume 138 , Issue 2 , April 2006 , pp. 253 - 262
Copyright
Copyright © Entomological Society of Canada 2006

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