Effect of different soils on pheromone enhanced movement of entomopathogenic nematodes

Authors: Gulzar, Sehrish; SLUSHER, EDDIE - Agrilife Research; KAPLAN, FATMA - Pheronym, Inc; HOBBS, STEVEN - Pheronym, Inc; LEWIS, EDWIN - University Of Idaho; Shapiro Ilan, David

Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Entomopathogenic nematodes (also known as beneficial nematodes) are small round worms that are used as biological control agents against different insect pests. Entomopathogenic nematodes occur naturally in soil environments, locate and kill their insect pest hosts with aid of symbiotic bacteria. Once nematodes consume an insect host, a special stage called the infective juvenile, develops inside the host, move to search for a new host. Beneficial nematodes typically move through the soil environment to find their next host. In previous research, nematode pheromones were used to enhance nematode movement and infectivity (ability to infect the insect). The outcome was that pheromones increase the beneficial nematodes’ ability to control pecan weevil in the greenhouse and in a pecan orchard. However, the effects of different soil types on the pheromone boosters have not been studied. So, the objective of the current research was to explore the use of pheromones to enhance beneficial nematode efficacy in different soils. The study was conducted in laboratory using different soils (commercial play sand, and two different pecan orchard soils). Results indicated pheromones enhanced biocontrol efficacy in all the soils tested. Additionally, the magnitude of pheromone impact was not different based on nematode species or soil. Therefore, we expect that pheromones can be used in diverse soil types to enhance the efficacy of entomopathogenic nematodes. The research expands the usefulness of beneficial nematodes as biocontrol agents.

Technical Abstract: Parasite movement within different substrates is an important factor for reaching a host and completing the parasitic life cycle. Entomopathogenic nematodes (EPNs) have a specialized infective juvenile stage (IJ), which is mobile and has the capability seek insect hosts to penetrate their haemocoel. EPNs are primarily applied to soil as biological control agents; thus, the IJs must move through the soil environment to find and then infect a host. In prior research, ascaroside pheromones were shown to enhance EPN movement and infectivity in soil. The ability of pheromones to enhance EPN efficacy was recently demonstrated under field conditions in a pecan orchard. Soil characteristics are known to be an important factor that can affect the efficiency of EPN movement behavior. However, prior to our research it was unknown whether different soils have differential effects on pheromone enhanced EPN efficacy. In different soils, we tested biocontrol efficacy of Steinernema carpocapsae, Steinernema feltiae and Heterorhabditis bacteriophora in soil columns with and without pheromone exposure. All nematodes were evaluated in separate columns filled with oven dried commercial play sand or two different soils from pecan orchards (from Byron, GA and Tifton, GA). The soils differed substantially in several aspects such as field capacity, organic matter, nutrients, and nematode movement capacity. Efficacy was determined by baiting the bottom section of each column with larvae of the yellow mealworm, (Tenebrio molitor L.). Results indicated that pheromones enhanced EPN efficacy for all species and soils relative to treatments without pheromone. Additionally, the magnitude/extent that pheromones boosted EPN movement did not differ based on EPN species or soils. Soil did not affect EPN efficacy for H. bacteriophora but did affect S. carpocapsae and S. feltiae. For both S. carpocapsae and S. feltiae efficacy was higher in the Tifton soil than the commercial play sand and the Byron pecan soil was intermediate. When comparing the efficacy of EPN species to each other, we observed that H. bacteriophora killed more bait insects exposed to soil in the bottom of the soil column than S. feltiae and S. carpocapsae. Based on our findings, we expect that pheromones can be used to enhance EPN efficacy in diverse soils. Future research may explore pheromone effects on EPNs in additional substrates.