Dr. Adler Dillman, professor of parasitology and the Chair of the Department of Nematology at the University of California Riverside (UCR), researches host parasite interactions, with emphasis on nematode parasites. Nematology is the scientific study of nematodes, a type of microscopic roundworms.
He began his exploration as a graduate student at the California Institute of Technology (CalTech), where he published draft genomes – incomplete versions of an organism’s genetic sequence – of entomopathogenic nematodes (EPNs) outlining their genetic material and refining their sequences. Dr. Dillman has been a professor at UCR since 2015 and continues his research on EPNs and further exploring their impact on insects.
Entomopathogenic nematodes are roundworm parasites that solely target insects and are
commonly used as biological insecticides. The primary host for these parasites are soil dwelling insects. These nematodes are sensitive to ultraviolet (UV) rays and desiccation, the removal of moisture, and have adapted to the body temperature of their insect hosts.
Insects are poikilothermic, meaning their body temperature fluctuates with the environment. These parasites enter the insects through bodily orifices, including the mouth, anus and spiracles, the insects’ respiratory openings. The nematode has two life stages. The free living stage is where the nematode freely roams in the soil. The active pathogenic stage is where it releases pathogenic material inside the insect.
Dr. Dillman is interested in understanding the nematode’s role in the process of liquefying the insect. He explained that when he was a student, “the dogma in the field was that the nematodes primarily serve as a vector – an organism that transmits pathogens to the host without being affected for this bacteria.” However, he wanted to explore whether the nematode itself plays a role in the toxicity.
When Dr. Dillman began working at UCR, he conducted experiments on nematodes, such as Steinernema carpocapsae, by manipulating them into sensing they were inside an insect to activate their response. This was achieved by placing the parasites in insect tissue cultured in petri dishes. Once the nematode has entered the insect tissue it ejects pathogenic saliva that liquifies its host, functioning as a natural insecticide.
Dr. Dillman focuses his research on this pathogenic saliva by collecting these samples and
identifying the proteins through mass spectrometry, a tool used for identifying chemical composition of organic samples. He found that the nematodes release a “cocktail” of proteins that are highly toxic to insects. His lab is continuing its investigation into which specific proteins are toxins.
In addition to studying insecticidal toxins, Dr. Dillman is investigating immunomodulatory proteins, proteins that regulate immune function, in nematodes saliva. He focuses on three individual proteins: a fatty acid and retinol binding protein, a phospholipase enzyme and a Sensor Histidine Kinase (SHK) domain-containing protein.
SHK plays a role in bacterial adaptation and antibiotic resistance. The SHK protein also induces paralysis by disrupting neurological signals to the brain. Dr. Dillman’s lab found that these three proteins enhance toxicity, particularly in younger insects. In the future Dr. Dillman aims to expand his research into parasites in dogs, specifically liver flukes.
