Regular Article
The Effects of Temperature on the Pathogenicity of Heat-Sensitive Mutants of the Entomopathogenic Fungus,Beauveria bassiana,toward the Migratory Grasshopper,Melanoplus sanguinipes

https://doi.org/10.1006/jipa.1996.0074Get rights and content

Abstract

Heat-sensitive (HS) mutants ofBeauveria bassianawere shown to kill grasshoppers at the growth-permissive temperature (PT) of 20°C but not at 30°C or more, the nonpermissive temperatures (NPT). The migratory grasshopper,Melanoplus sanguinipes,exhibited near complete poikilothermy in the bioassay system employed forB. bassianastrains. Temperature shift, from 20 to 30°C, during the bioassays was used to halt the mutant cell development postinfection. The resultant mortality data were analyzed using median effect plots. Timing of the infection was correlated with the required time at PT for grasshopper death. An incubation period of 4.6 to 6.4 days, postinfection, at PT was needed in order for the values for onset of infection, mortality rates, and the LT50for the three HS mutants to reach those insects infected with control strain, GK2016, at the PT. The time of PT exposure required to ultimately kill half of the test insect population, termed LE50, ranged from 3.9 to 5.1 days. A minimum time for the insect infection at PT, defined by the LE50value, is required for infection to lead to mortality. This time, the initial 4.4 days of infection, may reflect certain critical event(s) after which, whether or not additional fungal growth at NPT occurs, grasshopper death is unavoidable. These observations should help the development of models for predicting the outcome of infection processes and elucidation of critical events.

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1

Present address: Department of Zoology, University of British Columbia, 6270 University Blvd., Vancouver, BC, Canada V6T 1Z4.

2

To whom correspondence should be addressed.

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