Date of Award

2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Plant and Soil Science

First Advisor

Josef H. Görres

Abstract

Jumping worms (Megascolecidae) in the pheretimoid complex, have raisedconsiderable environmental concerns with conservationists, ecologists, policy makers, and the public. Their impacts on North American forests and high density is distinct from earthworms in other families. Most of the infested forests are near horticultural settings. Practicable options to manage their dispersal into forests do not exist. This dissertation examines the potential of an entomopathogenic fungus to control them in horticulture. It also investigates major barriers to managing their spread and studying their ecology including species identification, phenology, and genetic diversity. First, to discover the best time to apply biocontrol agents, I studied their phenology. This required accurate identification of the three co-occurring species: Amynthas tokioensis, A. agrestis, and Metaphire hilgendorfi, which are indistinguishable as juveniles and look similar even as adults. To this end, I developed a PCR speciesspecific multiplex method to identify pheretimoids accurately. Next, using the multiplex species-specific primers method I evaluated the population density of three different species over a period of a year from their cocoon stage to adulthood. I discovered that cocoons survive in soil for at least two years in high numbers, providing a cocoon bank. Using the PCR multiplex method, I was able to track hatching and development of the three sympatrically occurring species. The three species hatch at the same time and their populations develop together. Notably, peak abundance of pheretimoids occurred while they were still juveniles in May - June at forested sites in Vermont. I employed microsatellite loci for the two most common pheretimoid species in Vermont: A. agrestis and A. tokioensis. Using these molecular markers allowed me to investigate genetic diversity, clonality, and likely sources of pheretimoids at six sites, that included three forest, two nurseries and one home garden. Although these earthworms are believed to be parthenogenetic, microsatellite loci revealed high genetic diversity at the six populations in Vermont. This may suggest occasional sexual reproduction. Lineages occurring in nurseries were also observed in the forest areas, and home garden. This may suggest that the nurseries could be sources of dispersal through the state. Finally, I examined the effect of granular formulations of an entomopathogenic fungus, Beauveria bassiana and a commercial product on different life stages of pheretimoids. Granular formulation allows uniform distribution of the fungus and provides nutrients for the fungus to survive in the absence of the host. This pot-based greenhouse study mimicked conditions found in commercial horticulture. Mycotized millet caused high mortality (~80%) in juvenile stage. This is important because their phenology, i.e., peak abundance as juveniles, favors application of mycotized B. bassiana at this stage. The agent was less efficacious on adults (40% mortality) than juveniles. While mycotized millet was effective, the commercial product of B. bassiana used according to label had no efficacy on controlling pheretimoids. Collectively the results of this dissertation could be employed in designing strategies to control pheretimoid dispersal. Control efforts such as using B. bassiana should be focused on nurseries when they are in their highest abundance of juvenile stage and more susceptible to the fungus, rather than forests.

Language

en

Number of Pages

187 p.

Available for download on Saturday, January 07, 2023

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