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METARHIZIUM FLAVOVIRIDE (FI985) AS A PROMISING MYCOINSECTICIDE FOR AUSTRALIAN ACRIDIDS

Published online by Cambridge University Press:  31 May 2012

Richard J. Milner*
Affiliation:
Commonwealth Scientific and Industrial Research Organisatron (CSIRO), Division of Entomology, Canberra, Australia 2601
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Abstract

Only one isolate of Metarhizium flavoviride Gams and Roszypal group 3 has been isolated from a field-infected acridid in Australia. This is isolate FI985 (ARSEF 324) obtained from a spur-throated locust, Austracris guttulosa (Walker), near Rockhampton, Queensland, in 1979. In terms of conidial size and shape as well as phialide morphology, FI985 is intermediate between Metarhizium anisopliae (Metschnikoff) Sorokin and M. flavoviride. It has been compared with other group 3 isolates using RAPDs and sequence analysis of the ITS region and found to be very similar. However the analysis shows that these group 3 isolates are genetically closer to M. anisopliae than to M. flavoviride sensu stricto. Laboratory bioassays have shown that FI985 is virulent for five species of acridid pests in Australia. Comparative bioassays with other isolates of Metarhizium, including other group 3 isolates from Africa and Asia, have not yet revealed any isolate more virulent than FI985. This isolate is amenable to mass-production on rice and has been formulated in oil as a mycoinsecticide. The results from six field tests, mostly against wingless grasshopper, Phaulacridium vittatum (SjÖstedt), using doses of 2–7 × 1012 conidia per hectare and plot sizes up to 50 ha are summarized. These trials (with the exception of the first against the Australian plague locust) have given high levels of disease-related mortality in caged samples of the target collected within 3 days of spraying. In the four trials with wingless grasshopper, population reductions were detected 10–30 days after application; however these reductions were much less than suggested by cage samples as a result of movement of the target acridids. In contrast, positive control plots sprayed with fenitrothion gave a very high initial kill (>90% in 1 day) but were then more rapidly reinvaded. Consequently, 3–4 weeks after spraying the density in the plots treated with chemical insecticide and those treated with mycoinsecticide were similar. Further field trials are needed especially against the Australian plague locust and evaluating lower doses. The results obtained to date show that a mycoinsecticide based on FI985 is likely to be effective over a wide range of target acridids and weather conditions.

Résumé

Un seul isolat de Metarhizium flavoviride Gams and Roszypal du groupe 3 a été trouvé chez un criquet (Acrididae) d'Australie infecté en nature. Il s'agit de l'isolat FI985 (ARSEF 324) obtenu chez Austracris guttulosa (Walker), près de Rockhampton, Queensland, en 1979. L'isolat FI985 est intermédiaire entre Metarhizium anisopliae (Metschnikoff) Sorokin et M. flavoviride par la taille des conidies et la morphologie des phialides. L'isolat a été comparé à d'autres isolats du groupe 3 par amplification aléatoire d'ADN polymorphe (RAPD) et par analyse des séquences d'espacement interspécifique (région ITS) et il se sont tous avérés très semblables. Cependant l'analyse a démontré que ces isolats du groupe 3 sont plus apparentés génétiquement à M. anisopliae qu'à M. flavoviride sensu stricto. Des expériences en laboratoire ont démontré que l'isolat est virulent contre cinq espèces d'acridiens nuisibles en Australie. Des expériences comparatives au moyen d'autres isolats de Metarhizium, dont des isolats du groupe 3 d'Afrique et d'Asie, n'ont pas révélé d'isolat plus virulent que le FI985. Cet isolat est un bon sujet pour la production en masse sur le riz et il a servi de base à une préparation à l'huile pour servir de mycoinsecticide. Les résultats de six tests en nature, surtout contre le criquet Phaulacridium vittatum (SjÖstedt), au moyen de doses de 2–7 × l012 conidies per hectare dans des grilles échantillons pouvant atteindre 50 ha sont résumés ici. Ces expériences (à l'exception de la première contre le Criquet migrateur d'Australie), ont, après 3 jours, entraîné une forte mortalité reliée à la maladie chez des criquets cibles gardés en cage. Au cours des quatre expériences sur P. vittatum sur le terrain, des réductions des populations ont été enregistrées de 10–30 jours après le traitement, mais ces réductions se sont avérées moins importantes que celles prévues d'après les expériences sur les insectes en cage à cause des déplacements des criquets traités. En revanche, des grilles échantillons traitées au fenitrothion ont subi une forte diminution des effectifs au début (>90% en 1 jour), mais ont été réenvahies plus rapidement. Conséquemment, 3–4 semaines après les traitements, la densité dans les parcelles traitées au moyen d'un insecticide chimique et celle enregistrée dans les parcelles traitées au moyen du mycoinsecticide étaient semblables. D'autres expériences sur le terrain sont essentielles, particulièrement pour raffiner les méthodes de lutte contre le Criquet migrateur d'Australie et pour évaluer l'effet de doses plus faibles. Les résultats obtenus à ce jour indiquent qu'un mycoinsecticide à base de FI985 a de fortes chances d'être efficace dans la lutte contre bon nombre d'acridiens dans une gamme étendue de conditions climatiques. [Traduit par la Rédaction]

Type
Research Article
Copyright
Copyright © Entomological Society of Canada 1997

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