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SUSCEPTIBILITY OF THE MIGRATORY GRASSHOPPER, MELANOPLUS SANGUINIPES (FAB.) (ORTHOPTERA: ACRIDIDAE), TO BEAUVERIA BASSIANA (BALS.) VUILLEMIN (HYPHOMYCETE): INFLUENCE OF RELATIVE HUMIDITY

Published online by Cambridge University Press:  31 May 2012

S. Marcandier  and
G.G. Khachatourians
S. Marcandier
Affiliation:
Bioinsecticide Research Laboratory, Department of Applied Microbiology and Food Science, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 0W0
G.G. Khachatourians*
Affiliation:
Bioinsecticide Research Laboratory, Department of Applied Microbiology and Food Science, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 0W0
*
2 Author to whom correspondence should be addressed.
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Abstract

In laboratory tests, Melanoplus sanguinipes (Fab.) was susceptible to infection by Beauveria bassiana (Bals.) Vuillemin conidia. Infection occurred independently of the relative humidity (RH) (12, 33, 76, 100% RH). No significant difference was observed in the final percentage mortality of the treated grasshoppers and in the lethal times (LT50)(P > 0.05) under the RH conditions studied. However, the daily rate of mortality after treatment was higher at 76% RH than at 33% RH. High natural mortality occurred at 100% RH.

At 100% RH, treatment with B. bassiana was associated with an outgrowth of microorganism that created septicemic conditions in the absence of the characteristic symptoms of mycosis. Below 100% RH, mycelial growth on cadavers was never observed, even though partial or total insect mummification occurred, and a pink body coloration on approximately 80% of the insects indicated Beauveria as the killing agent. Once transferred to 100% RH, no more than 5% of the treated grasshoppers exhibited external mycelial growth.

The microenvironment at the cuticular level of the grasshopper allows expression of conidial pathogenicity regardless of ambient RH. Hence, together, these observations suggest the feasibility of field testing with B. bassiana as a bioinsecticide against M. sanguinipes in semi-arid climatic areas.

Résumé

Melanoplus sanguinipes (Fab.) est sensible aux conidies du champignon Beauveria bassiana (Bals.) Vuillemin dans les conditions testées au laboratoire. Le processus infectieux se développe quel que soit le taux d’humidité relative (HR) (12, 33, 76 et 100%). Le pourcentage final de mortalité des insectes traités avec Beauveria est comparable dans tous les cas. Les temps léthaux (TL50) ne sont pas significativement différents (P > 0.05). Cependant le taux journalier de mortalité est supérieur à 76% HR par rapport à 33% HR. Un fort pourcentage de mortalité naturelle est observé lorsque le degré hygrométrique atteint le point de saturation.

À 100% HR, le traitement avec B. bassiana est associé au développement de microorganismes ce qui se traduit par un taux élevé de septicémies et l’absence des symptômes caractéristiques des mycoses à muscardine. Dans des conditions d’humidité relative non saturantes, la présence de mycelium sur les cadavres mommifies n’a jamais été observée, bien que la mommification totale ou partielle et la coloration rose, d’environ 80% des insectes, indique que Beauveria était l’agent pathogène responsable de leur décès. Une fois replacés à 100% HR pas plus de 5% des insectes n’ont présenté de croissance mycelienne externe.

Le microenvironnement au niveau cuticulaire est favorable à l’expression du pouvoir pathogène des spores quelle que soit l’humidité relative environnante. Cette observation permet donc d’envisager de tester B. bassiana en tant que bioinsecticide contre M. sanguinipes, en plein champ, en zones climatiques semi-arides.

Type
Articles
Information
The Canadian Entomologist , Volume 119 , Issue 10 , October 1987 , pp. 901 - 907
Copyright
Copyright © Entomological Society of Canada 1987

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