Erynia Radicans: Studies on Its Distribution, Pathogenicity, and Host Range in Relation to the Potato Leafhopper, Empoasca Fabae (Temperature Relationships, Scanning Electron Microscopy, Epizootiology, Illinois)
Mcguire, Michael Raymond
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https://hdl.handle.net/2142/71099
Description
Title
Erynia Radicans: Studies on Its Distribution, Pathogenicity, and Host Range in Relation to the Potato Leafhopper, Empoasca Fabae (Temperature Relationships, Scanning Electron Microscopy, Epizootiology, Illinois)
Author(s)
Mcguire, Michael Raymond
Issue Date
1985
Department of Study
Entomology
Discipline
Entomology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Entomology
Abstract
The potato leafhopper, Empoasca fabae is a serious economic pest of several agronomically important crops. Erynia radicans is a fungal pathogen that infects E. fabae and, at times, causes massive epizootics in Wisconsin. E. radicans has never been observed in Illinois populations of E. fabae despite well over twenty years of research with the pest. Studies were conducted to examine some of the factors involved in the distribution, host range, and epizootiology of E. radicans. Preliminary experiments indicated that scanning electron microscopy may be a very important method in observing some of the early processes involved in host susceptibility to E. radicans. Specimens fixed in osmiuns tetroxide vapors and then air dried were suitable for the direct observation of E. radicans conidia on intact insect cuticle. A host range study utilizing species of insects in culture yielded five susceptible homopteran species out of eight tested. Three lepidopteran species were tested and no individuals were infected. Because of the observed geographic distributions of E. radicans, studies on the effect of temperature on growth, sporulation and success of field introductions were conducted. E. radicans grew both in vitro and in vivo at constant temperatures of 28(DEGREES)C and below but not at 30(DEGREES)C or above. Conidial germination followed a similar temperature relationship.
E. radicans did not cycle through a caged population of E. fabae despite the occurrence of infections immediately following fungal release. Similarly, E. radicans did not become established following release into field populations of E. fabae in three areas of Illinois. Although initial infections were observed at two sites and horizontal transmission probably occurred at one site, epizootics did not develop. Temperatures exceeded the laboratory threshold for growth of E. radicans at all three sites but for different durations at each site. An epizootic of E. radicans occurred in E. fabae populations in Champaign County, Illinois the following year. Infection rates reached 93.4% in the nymph populations in a potato plot causing a dramatic population crash.
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