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SEASONAL PATTERNS OF CADAVER PERSISTENCE AND SPORULATION BY THE FUNGAL PATHOGEN ENTOMOPHAGA GRYLLI (FRESENIUS) BATKO (ENTOMOPHTHORALES: ENTOMOPHTHORACEAE) INFECTING CAMNULA PELLUCIDA (SCUDDER) (ORTHOPTERA: ACRIDIDAE)

Published online by Cambridge University Press:  31 May 2012

A.J. Sawyer ,
M.E. Ramos ,
T.J. Poprawski ,
R.S. Soper  and
R.I. Carruthers
A.J. Sawyer
Affiliation:
U.S. Department of Agriculture, Agricultural Research Service, Plant Protection Research Unit, U.S. Plant, Soil & Nutrition Laboratory, Ithaca, New York, USA 14853
M.E. Ramos
Affiliation:
U.S. Department of Agriculture, Agricultural Research Service, Plant Protection Research Unit, U.S. Plant, Soil & Nutrition Laboratory, Ithaca, New York, USA 14853
T.J. Poprawski
Affiliation:
U.S. Department of Agriculture, Agricultural Research Service, Plant Protection Research Unit, U.S. Plant, Soil & Nutrition Laboratory, Ithaca, New York, USA 14853
R.S. Soper
Affiliation:
U.S. Department of Agriculture, Agricultural Research Service, Plant Protection Research Unit, U.S. Plant, Soil & Nutrition Laboratory, Ithaca, New York, USA 14853
R.I. Carruthers
Affiliation:
U.S. Department of Agriculture, Agricultural Research Service, Plant Protection Research Unit, U.S. Plant, Soil & Nutrition Laboratory, Ithaca, New York, USA 14853
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Abstract

Entomophaga grylli (Fresenius) Batko (North American pathotype 1) is a fungal pathogen of the clearwinged grasshopper, Camnula pellucida (Scudder). We present results from a field experiment conducted in Arizona in 1984, designed to investigate factors associated with seasonal patterns of cadaver persistence and sporulation by E. grylli. Rangeland plots at two sites were monitored daily for 8 weeks for the appearance of new cadavers of diseased grasshoppers during a natural epizootic. Cadavers were individually marked and revisited on subsequent days, when it was noted whether or not conidial sporulation was underway. Environmental variables were recorded by electronic data loggers. Daily probabilities of cadaver disappearance and fungal sporulation were analysed in relation to site, date, and various measures of cadaver status, sporulation history, and environmental variables by logistic regression analysis. The average daily rate of cadaver disappearance was 0.22, yielding an expected time to 50% disappearance of 2.8 days. The environmental factor most significantly associated with cadaver disappearance was rainfall, and the most important host factor was age of the cadaver. The probability that conidia would be discharged from a cadaver over the next 24 h was most dependent on whether or not conidial sporulation was underway already. This probably reflects a state of readiness for sporulation on the part of the fungus. Although the probability of sporulation declined with increasing age of a cadaver, high rates of sporulation were predicted under conditions of prolonged leaf wetness and high humidity at night, regardless of age of the cadaver. These results, together with the observation that in some cadavers sequences of sporulation were interspersed with periods of no sporulation, suggest that E. grylli may undergo cycles of dehydration and rehydration, in which conidial production is interrupted and then resumes in response to changing environmental conditions.

Résumé

Entomophaga grylli (Fresenius) Batko (pathotype nord américain 1) est un cryptogame pathogène du criquet pellucide, Camnula pellucida (Scudder). Nous présentons les résultats d'une expérience menée au champ en Arizona en 1984, expérience visant à examiner les facteurs associés au modèle saisonnier de la persistance des cadavres mycosés et à celui de la sporulation d'E. grylli. L'apparition quotidienne de nouveaux cadavres de criquets infectés fut suivie pendant 8 semaines lors d'une épizootie naturelle dans des parcelles de paturâge situées en deux sites. Les cadavres furent marqués individuellement et observés durant les jours subséquents afin d'établir si la sporulation était en cours ou non. Les variables du milieu environnant furent enregistrées au moyen d'un système électronique d'acquisition de données. La probabilité quotidienne de la disparition des cadavres et de celle de la cessation de la sporulation du cryptogame en relation avec le site, la date, et diverses mesures de l'état des cadavres, de l'historique de la sporulation et des variables du milieu environnant furent analysées par la régression logistique. Le taux de disparition des cadavres moyen quotidien fut 0,22, produisant un temps de disparition de 50% attendu de 2,8 jours. La variable du milieu environnant la plus significativement associée à la disparition des cadavres fut la pluviosité alors que la variable hôte la plus importante fut l'âge du cadavre. La probabilité que les conidies seraient projetées à partir d'un cadavre durant les prochaines 24 h fut surtout dépendante du fait que la sporulation était déjà en cours. Ceci reflète probablement un état de préparation à la sporulation de la part du cryptogame. Bien que la probabilité de la sporulation déclina avec le vieillissement d'un cadavre, des taux de sporulation élevés furent prédits sous conditions d'humectation du feuillage prolongée et d'humidité nocturne élevée, peu importe l'âge du cadavre. Ces résultats, ajoutés au fait que chez certains cadavres les séquences de la sporulation étaient parsemées de périodes sans sporulation, suggèrent qu'E. grylli peut subir des cycles de déshydratation et de réhydratation durant lesquels la production de conidies est interrompue et alors réassumée en réponse aux conditions changeantes du milieu environnant.

Type
Research Article
Information
The Memoirs of the Entomological Society of Canada , Volume 129 , Supplement S171 , 1997 , pp. 355 - 374
Copyright
Copyright © Entomological Society of Canada 1997

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Footnotes

1

Mention of a commercial or proprietary product does not constitute an endorsement or a recommendation for its use by the USDA.

2

Current address: USDA-APHIS-PPQ, Hawaii Plant Protection Center, PO Box 1040, Waimanalo, Hawaii, USA 96795.

3

Current address: USDA-ARS Subtropical Agriculture Research Laboratory, Biological Pest Control Research and Texas A&M Agricultural Experimental Station, 2413 East Hwy 83, Weslaco, Texas, USA 78596.

4

Current address: USDA-ARS, International Activities, Building 005, Beltsville Agricultural Resetrch Center West, Beltsville, Maryland, USA 20705.

5

Current address: USDA-ARS, National Program Staff, Building 005, Beltsville Agricultural Research Center-West, Beltsville, Maryland, USA 20705.

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