THE ECOLOGY OF INSECT MEDIATED TRANSMISSION OF THE FIRE BLIGHT PATHOGEN, ERWINIA AMYLOVORA, BY ORCHARD DWELLING DIPTERANS

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Abstract

Fire blight, caused by the bacterial pathogen Erwinia amylovora, is a devastating disease of pome fruit with worldwide distribution. The disease gets its name from the scorched appearance of diseased tissue and infects all tissue types of pomaceous fruit. Tissue in the early stages of infection exude a bacterial ooze containing the bacteria in a polysaccharide matrix, which acts as primary and secondary inoculum. Insects have been implicated in the transmission of E. amylovora since the pathogen was first discovered, with various mechanisms for insect mediated transmission proposed. The goal of this research was to further define the role of insects in transmission of E. amylovora by identifying its most important potential vectors in New York State and advancing our knowledge of the ecology of transmission by insects. In chapter 1, we describe field surveys used to identify key insect vectors over the course of a growing season, showing that while pollinating hymenopterans historically received attention as springtime disease disseminators, dipterans have an understudied and potentially outsized role in transmission throughout the entire season. Various families of Diptera were observed feeding on bacterial ooze and could shed bacteria for at least six days following an acquisition event from ooze. In chapter 2, we use lab bioassays to investigate biological factors affecting the ability of Drosophila melanogaster to acquire and transmit E. amylovora, showing that mating status, nutritional state, and sex had no effect on acquisition and transmission. The data presented in this chapter supports earlier hypothesis outlining Diptera as mechanical vectors. In chapter 3, we showed that Delia platura, an anthomyiid, can successfully initiate new infections in damaged apple saplings, and demonstrated that the bacterium has no deleterious effects on the flies. Based on this data, we suggest that the relationship between D. platura and E. amylovora is at least commensal and possibly mutualistic, wherein the fly benefits by using ooze as a food source and the bacterium benefits by insect mediated transmission. In chapter 4, we showed that E. amylovora has minor behavioral effects on D. platura, but further research is required to understand how these changes in behavior impact disease transmission success. Collectively, this work provides a roadmap for the future study of insect mediated transmission of E. amylovora. The role of Diptera in the disease cycle is clear and has been largely ignored for more than 120 years. We argue for greater attention to the details of Diptera driven transmission, especially relating to insect behavior, as this space within the disease cycle has largely untapped potential to benefit management and disease outbreak models.

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176 pages
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2020-08
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Keywords
Delia platura; Erwinia amylovora; Fire Blight; Ooze
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Union Local
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Committee Chair
Loeb, Gregory M.
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McArt, Scott
Cox, Kerik D.
Degree Discipline
Entomology
Degree Name
Ph. D., Entomology
Degree Level
Doctor of Philosophy
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Government Document
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Attribution-NonCommercial-NoDerivatives 4.0 International
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dissertation or thesis
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