Physical Properties of Soils Altered by Invasive Pheretimoid Earthworms: Does Their Casting Layer Create Thermal Refuges?

Pheretimoid earthworms are invasive in hardwood forests of formerly glaciated regions in the USA. They alter the forest floor structure by creating an extensive, several cm-deep casting layer comprising loose macro-aggregates. Little is known about the physical properties of the casting layer and how they relate to earthworm ecology. Here, thermal and macropore properties of three forest soil textures (clay, silt, and sandy soils, with and without pheretimoids) were measured and compared to explore the possible relationships to their ecology. Thermal properties were significantly different between the casting layer (CAST) and original soil (NOCAST). Results indicate that CAST soils dampen temperature fluctuations occurring at the surface more than NOCAST soil. The increased dampening may be of particular importance to pheretimoid survival in forest fires and during spring when surface fluctuations could expose the hatchlings to fatal temperatures. Macropore volume, an indicator of ease of movement of pheretimoids, was significantly greater in CAST than NOCAST soil. Together, the ease of movement and greater temperature dampening of CAST soils may provide thermal refuges to pheretimoids from temperature variations outside the optimal range. This may improve their chances of survival in newly colonized areas where the climate differs from the original range.University of Vermont's Agricultural Research Station [1018366]; Turkish Scientific and Technological Research Council, TUBITAKTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [2219]This research was funded by The University of Vermont's Agricultural Research Station (Hatch 1018366) and the Turkish Scientific and Technological Research Council, TUBITAK (International Post-Doctoral Research Fellowship 2219)

Tools for monitoring and study of peregrine pheretimoid earthworms (Megascolecidae)

Peregrine pheretimoid earthworms, commonly known as jumping worms, are members of the family Megascolecidae that have become widely established outside of their native ranges. In many parts of the world this represents a second wave of earthworm invasions, following the introduction of peregrine European earthworms in the family Lumbricidae during the colonial era. Forest ecologists, turf managers, gardeners, and other land managers are concerned about the observed or presumed negative effects of jumping worms on invaded habitats. Although research on jumping worms has accelerated in recent decades, our understanding of their ecology remains limited. We compiled techniques useful to researchers working to fill voids in our understanding. Similar past efforts have focused on tools used to study common European species. Differences in life cycle, behavior, morphology, and physiology make it difficult to transfer experiences with European earthworms to pheretimoids. For example, the loss of reproductive features in many pheretimoid populations poses a challenge for identification, and techniques for individually tagging lumbricid earthworms have been less successful for megascolecids. The active and ongoing expansion of pheretimoid populations in many areas requires increased attention on distributed methods, such as citizen-science protocols, for detecting and tracking their expansion. Finally, the desire to limit populations of pheretimoids, including those invading gardens and other environments that might be successfully restored, has exposed the lack of options for targeted, effective control of unwanted earthworms. We identify opportunities to address these voids in our methodological tool kit and encourage the adaptation of techniques previously used in the study and management of other invasive animals

Elements Of Biocontrol Strategies For Pheretimoid Earthworms

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

The second wave of earthworm invasions in North America: biology, environmental impacts, management and control of invasive jumping worms

The invasion of jumping worms, a small group of pheretimoid earthworm species from Asia, has increasingly become an ecological, environmental and conservation issue in forest ecosystems and urban-suburban landscapes around the world. Their presence is often noticed due to their high abundance, distinctive “jumping” behavior, and prominent granular casts on the soil surface. Although they are known to affect soil carbon dynamics and nutrient availability, no single paper has summarized their profound impacts on soil biodiversity, plant community, and animals of all trophic groups that rely on soil and the leaf litter layer for habitat, food, and shelter. In this study, we summarize the biology, invasion, and ecological impacts of invasive jumping worms across North America. We highlight potential impacts of this second wave of earthworm invasion, contrast them with the preceding European earthworm invasion in temperate forests in North America, and identify annual life cycle, reproductive and cocoon survival strategies, casting behavior and co-invasion dynamics as the key factors that contribute to their successful invasion and distinct ecological impacts. We then suggest potential management and control strategies for practitioners and policy makers, underscore the importance of coordinated community science projects in tracking the spread, and identify knowledge gaps that need to be addressed to understand and control the invasion