Phasmarhabditis hermaphrodita, a gastropod specific facultative parasite, has been used as a successful biological control agent across Europe under the brand name Nemaslug®. However, Phasmarhabditis nematodes have not been permitted for use in the United States since that they had not been found locally within the country. We surveyed nurseries and garden centers throughout California and identified local populations of Phasmarhabditis including Phasmarhabditis californica, P. hermaphrodita, Phasmarhabditis papillosa, and another close relative to P. papillosa. We also described the hosts which the nematodes were found in. P. hermaphrodita and P. californica seem to share an environmental niche in Northern and Central California while P. papillosa was only found in Southern California. We also tested the pathogenicity of the discovered local Phasmarhabditis strains against the invasive snail Theba pisana. The assays were performed to assess the efficacy of the strains as biological control agents. All tested strains caused significant mortality against adult T. pisana at five times the Nemaslug® recommended dose (150 IJs/cm2 ). Upon further assessment using only P. californica, it was found that the strain was not capable of causing an economically significant amount viii of mortality to T. pisana at the recommended rate (30 IJs/cm2 ) or at three times the recommended rate (90 IJs/cm2 ). Lastly, we decided to assess the native microbiome of local Phasmarhabditis isolates discovered during our surveys. The microbiome of the gastropod specific parasites is not well studied. Our surveys presented great opportunities for us to explore their microbiomes across a large geographic region in their natural habitats. The microbiome assessments were performed via 16S sequencing of Phasmarhabditis nematodes freshly identified from gastropod cadavers. We found that their microbial community was influenced by nematode species, location, and gastropod host from which the nematode was collected. The predominant bacteria of the isolates included Shewanella, Clostridium perfringens, Aeromonadaceae, Pseudomanodaceae, and Acinetobacter, with some nematode species having more frequent associations with certain bacterial species than others. These discoveries on the local strains of Phasmarhabditis support the possibility of these nematodes as a biological control option within the United States.

Entomopathogenic nematodes (EPNs) are insect-parasitic nematodes that rapidly kill insects and have been used for biocontrol of insect pests. The symbiotic bacteria that these EPNs carry have traditionally been thought to be the only source of virulence, however, we have shown substantial proof that these nematodes do actively contribute to killing the insect-host. We show that EPNs from the genus Steinernema release excreted-secreted proteins (ESPs) at the early stages of infecting a host and these ESPs are toxic to insects. This paradigm shift in the EPN field merited further exploration into the mechanisms of toxicity of the nematode derived ESPs. Profiling of the ESPs revealed a complex mixture of proteins predicted to be involved in tissue damage and host immune modulation. Many of these proteins were also found to be highly similar to proteins used by vertebrate parasites. We found a core suite of proteins utilized by two Steinernema species of EPNs at the early stages of infection indicating these proteins have a central and important role in insect-parasitology and potentially vertebrate-parasitology as well. We continue to identify candidate active proteins in the ESPs of Steinernema feltiae and produce these proteins for characterization.

Parasitic nematodes cause significant morbidity and mortality to humans. Much of their ability to successfully infect their hosts is due to the variety of excreted/ secreted proteins (ESPs) they release into host tissues, and their ability to evade or suppress host immunity, yet little is known about the mechanisms behind these interactions. This work identifies and characterizes two ESPs that display immunomodulatory activity in the model host Drosophila melanogaster. The fatty acid- and retinol- binding (FAR) proteins and the secreted phospholipase A2 (sPLA2) enzyme from the entomopathogenic nematode Steinernema carpocapsae likely elicit their detrimental effects by preventing essential immune lipid signaling in the fly. The FAR proteins bind to fatty acids and retinol and alter the in vivo availability of lipids in the fly hemolymph. They also function to suppress phenoloxidase activity and antimicrobial peptide production, both of which are essential in the fly’s ability to resist bacterial infections. In contrast, the sPLA2 enzyme cleaves lipids directly from the membrane and shows specific immunomodulatory effects on toll signaling and phagocytosis. Overall analysis of fly hemolymph post infection revealed several lipids that are depleted and are also able to rescue to course of infection. This work identifies lipids and prostaglandins that significantly improve the outcome of infection, furthering our understanding of the role of lipids and eicosanoids in Drosophila immunity.

Entomopathogenic nematodes (EPNs) are insect-killing parasitic worms that are utilized in agriculture and home-garden use against a variety of insect pests. It is the infective juvenile stage (IJ) of the EPN life cycle responsible for locating, infecting and colonizing a new insect host to continue the life cycle and produce progeny. My research revealed that EPN species within the genus Steinernema, responded to host volatiles, in species—specific patterns with regard to both behavioral trends to the progression of infection, as well as overall participation. Analysis of host-odor profiles- for both naive and infected hosts (including recently infected and long-term, resource depleted insect cadavers) produced a variety of odors and one of the more notable odors produced was 3-methyl-2-buten-1-ol (prenol). EPN IJs were found to be repelled by prenol at a variety of doses (ranging from 2M to 20mM) and prenol yielded age-dependent increases in dispersal, implicating prenol as a potential IJ dispersal cue. However, lack of molecular tools in EPNs prevented investigations into the molecular underpinnings of how prenol is detected and translated into the observable repulsion. To overcome this obstacle, we leveraged the model organisms: Caenorhabditis elegans which exhibits attraction to prenol. Through use of natural variation, genome-wide association, and leveraging multiple genetic resources in the C. elegans community we identified the involvement of the AWC neuron in detection and response to prenol as well as eight genes that influence responses to prenol, including genes that have not previously been shown to affect chemotactic behaviors: dod-17, clec-39, dcap-1 and dcap-2. For many of these genes, we have found EPN orthologs exist, meaning we have uncovered information that potentially could be utilized to better understand EPN behavioral ecology such that EPNs may be improved or utilized more effectively in the future.