**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** HERBIVORES OF PLANT ROOTS ARE AMONG THE MOST ECONOMICALLY DEVASTATING CROP PESTS BECAUSE THEIR UNDERGROUND INFESTATIONS ARE CHALLENGING TO DETECT AND DIFFICULT TO CONTROL. CONVENTIONAL STRATEGIES FOR MANAGING ROOT HERBIVORES OFTEN RELY ON PROPHYLACTIC PESTICIDE APPLICATIONS, WHICH CAN BE EXPENSIVE FOR FARMERS AND DAMAGING TO THE ENVIRONMENT. BIOLOGICAL CONTROL, WHERE BENEFICIAL ORGANISMS ARE INTRODUCED TO KILL PESTS, IS A PROMISING STRATEGY FOR IMPROVING SUSTAINABILITY IN PEST MANAGEMENT AND REDUCING RELIANCE ON INSECTICIDES. BENEFICIAL INSECT-KILLING NEMATODES (EPNS) ARE SOME OF THE MOST PROMISING ORGANISMS FOR BIOLOGICAL CONTROL OF SOIL-DWELLING INSECT PESTS, AS THEY SEEK AND KILL ROOT-FEEDING HERBIVORES. HOWEVER, EPN BIOCONTROL IS STILL NOT WIDELY USED IN U.S. AGRICULTURE AND REPRESENTS ONLY A SMALL FRACTION OF THE U.S. PEST CONTROL MARKET. A MAJOR GOAL OF THIS PROJECT IS TO UNCOVER ADDITIONAL BENEFITS AND NEW TECHNIQUES FOR EPN BIOLOGICAL CONTROL TO IMPROVE ITS EFFECTIVENESS AND INCREASE ADOPTION RATES AMONG FARMERS. WE WILL EXAMINE HOW BENEFICIAL EPNS CAN INCREASE PLANT PROTECTION BY BOOSTING PLANT RESISTANCE AGAINST A VARIETY OF PESTS. OUR PRELIMINARY FINDINGS SUGGEST THAT EPNS PRODUCE CHARACTERISTIC CHEMICAL CUES AND THAT PLANTS RESPOND TO THESE CUES BY ENHANCING THEIR DEFENSES AGAINST HERBIVORES AND PATHOGENS. WE WILL ALSO INVESTIGATE HOW PLANT RESPONSES TO EPN CUES AFFECT PLANT ASSOCIATIONS WITH BENEFICIAL ORGANISMS, LIKE GROWTH-PROMOTING FUNGI AND OTHER BENEFICIAL NEMATODES. THE FINDINGS FROM THIS RESEARCH WILL INCREASE OUR KNOWLEDGE ABOUT EPN ECOLOGY AND BIOLOGICAL CONTROL, WHICH WILL GREATLY ADVANCE THE FIELDS OF NEMATOLOGY, CHEMICAL ECOLOGY, AND PLANT BIOLOGY. THIS RESEARCH WILL ALSO CONTRIBUTE TO IMPROVING SUSTAINABLE PEST MANAGEMENT BY IDENTIFYING NEW APPROACHES FOR HARNESSING ECOLOGICAL INTERACTIONS IN AGRICULTURAL SYSTEMS.