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United States Department of Agriculture

Agricultural Research Service

Title: Effect of Relative Humidity on Viability of Primary Conidia of Zoophthora Radicans

Authors
item Vandenberg, John
item Griggs, Michael
item Sawyer, Alan - USDA APHIS

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 15, 1998
Publication Date: N/A

Interpretive Summary: The potato leafhopper is a key pest of alfalfa and other crops throughout the United States. The fungus Zoophthora radicans is an important pathogen of this insect with potential to cause natural disease outhbreaks within leafhopper populations. In order to use it as a control agent, an appropriate strain must be selected. For this study we determined the effect of humidity on spore survival for 4 fungal strains obtained from th U.S., Brazil, Israel and Yugoslavia. Given the relatively small differences we found among fungal strains, selection of a strain for use in biological control efforts can be focused on other traits. For example, our results showed that at 80 percent or greater humidity, more than half the fungus spores survived up to 4 hours. This is sufficient time, even at low wind velocitites, for spore dispersal over considerable distances. Future work can be directed at understanding the process of spore dispersal and disease espread within pest insect populations.

Technical Abstract: Four isolates of the entomopathogenic fungus Zoophthora radicans were compared in a laboratory study to evaluate the effect of relative humidity (RH) on duration of primary conidial viability. Conidial samples of each isolate were incubated for 5 to 240 minutes at each of five test RH levels and then removed and inspected using a technique of simultaneous vital fluorochrome staining to determine percentage conidial viability. At 60 percent RH, isolates did not differ significantly and average viability dropped to less than 10 percent within the first 60 minutes. At 75 percent viability did not change significantly over 4 h. However, average viabilities at 75 percent RH differed significantly for the 4 isolates and ranged from 24 to 63 percent. At 80 percent RH viability differed significantly among isolates and declined slowly over time, remaining above 80 percent for 2 h and above 50 percent for 4 h. At 95 and 100 percent RH average viability was near 95 percent and did not vary significantly with time or isolate. Given the relatively small differences among isolates, selection of an isolate for use in biological control efforts can be focused on other traits.

Last Modified: 9/20/2014
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