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ATTEMPTS TO INCREASE THE PREVALENCE AND SEVERITY OF INFECTION OF GRASSHOPPERS WITH THE ENTOMOPATHOGEN NOSEMA LOCUSTAE CANNING (MICROSPORIDA: NOSEMATIDAE) BY REPEATED FIELD APPLICATION

Published online by Cambridge University Press:  31 May 2012

Dan L. Johnson  and
Michael G. Dolinski
Dan L. Johnson
Affiliation:
Land Resource Sciences, Agriculture and Agri-Food Canada, Research Centre, P.O. Box 3000, Lethbridge, Albeta, Canada T1J 4B1
Michael G. Dolinski
Affiliation:
Alberta Agriculture, Food and Rural Development, 7000 - 113 Street, Edmonton, Alberta, Canada T6H 5T6
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Abstract

Initial promising results with the microsporidium Nosema locustae Canning as a means of controlling grasshoppers have been followed by some cases of limited field performance. However, at sublethal doses this entomopathogen can reduce grasshopper feeding, reproduction and development, suggesting that the damage caused to range, forages and crops might be reduced if the prevalence of infection in the field could be increased over previously achieved levels. In a field experiment, we treated plots totalling 780 ha with bran bait containing N. locustae at either 2.5 or 5.0 × 109 spores per ha in each of two consecutive years, and grasshopper populations and the prevalence and degree of infection were monitored every two weeks during the summers, for three years. Little or no background infection occurred in the untreated plots. Infections of grasshoppers with N. locustae in the treated plots during the first year of application, typically increased from less than 5% by the 4th week to 10–15% by the 8th week after application. The higher application rates resulted in only slightly higher percentages infected. Most of the infections were classified by microscopic examination as trace to moderate, although heavy infections were observed in the second year. Up to 35% of some Melanoplus species collected from the treated plots were found to contain N. locustae spores, but intensive monitoring indicated population reductions that were inconsistent among sites and generally less than 50%. Other species, notably Aeropedellus clavatus, Ageneotettix deorum, Bruneria brunnea and Camnula pellucida, failed to acquire significant infection by N. locustae. The presence of these apparently less susceptible species did not account for the poor overall performance of the treatments. Two annual applications of N. locustae did not greatly increase the rate or severity of infections in grasshopper populations, although at one of the three sites, trace infections were found in the treated plots six years later.Although Nosema may eventually have value as a component of an integrated grasshopper pest management system, the low virulence cannot be readily overcome by repeated applications.

Résumé

Le succès prometteur As Nosema locustae Canning (Microsporida) comme agent de lutte contre les criquets au cours d'expériences préliminaires a été suivi de résultats assez décevants sur le terrain. Cependant, à des doses sublétales, cet entomopathogène peut réduire l'alimentation des criquets, leur reproduction et leur développement, nous permettant de croire que les dommages causés dans les pâturages et dans les cultures pourraient être réduits par augmentation de la gravité des infections. Au cours d'une expérience en nature, nous avons traité des parcelles de terrain totalisant 780 ha en répandant du son infecté par N. locustae à raison de 2,5 ou 5,0 × 109 spores par ha au cours de 2 années consécutives; l'importance des populations de criquets, de même que la fréquence et la gravité des infections ont été notées toutes les 2 semaines au cours de l'été pendant 3 ans. Peu d'infections, (ou alors aucune), ont été relevées dans les parcelles non traitées. Les infections des criquets dans les parcelles traitées au cours de la 1ière année après l'infection avaient augmenté de 5% à la 4e semaine et de 10–15% à la 8e semaine. L'application de concentrations plus élevées n'a donnée qu'une faible augmentation du pourcentage de criquets infectés. à l'examen microscopique, la plupart des infections se sont révélées légères ou modérées, mais des infections plus graves ont été observées au cours de la 2e année. Jusqu'à 35% de certains espèces deMelanoplus recueillies dans les parcelles traitées contennaient des spores de N. locustae, mais un examen intensif a révélé que les réductions de populations n'étaient pas les mêmes partout et s'élevaient rarement au-delà de 50%. Chez d'autres espèces, notamment Aeropedellus clavatus, Ageneotettix deorum, Bruneria brunnea et Camnula pellucida, les infections étaient négligeables. La présence de ces espèces apparemment moins sensibles n'explique pas la performance généralement faible des traitements. Deux applications annuelles de N. locustae n'ont pas augmenté considérablement la fréquence ou la gravité des infections chez les populations de criquets, même si, à l'un des trois sites, des infections légères prévalaient toujours dans les parcelles traitées 6 ans après l'application.

Nosema deviendra peut-être éventuellement une composante utile dans les programmes de lutte intégrée contre les criquets, mais il est certain que sa faible virulence ne peut être compensée par des applications répétées. [Traduit par la rédaction]

Type
Research Article
Information
The Memoirs of the Entomological Society of Canada , Volume 129 , Supplement S171 , 1997 , pp. 391 - 400
Copyright
Copyright © Entomological Society of Canada 1997

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