Foraging efficacy of entomopathogenic nematodes in different soil types from California citrus groves

Entomopathogenic nematodes (EPNs) are lethal insect parasites that develop inside the body of their insect-host. They can infect many different types of soil insects, including larval forms of the invasive citrus root weevil, Diaprepes abbreviatus which is a key pest in citrus production. Characteristics of soils have a great impact on the ability of EPNs to be used successfully in biological control programs. Our goal is to test the effectiveness of EPNs in soils from California citrus groves. Our specific objectives are to: 1) survey for the presence of native EPNs in California citrus groves; and 2) compare the efficacy of the EPN Steinernema riobrave in various soil types from California citrus groves. The long-term objective of this study is to develop biocontrol methods to address the invasion of the citrus root weevil, D. abbreviatus, into California using EPNs. We collected soils from 25 California citrus production sites, sampled them for native nematode presence and tested the foraging efficacy (movement and host finding) of S. riobrave within these soils at 3 different soil depths; 10, 25 and 50 cm. Soil textures and physical characteristics were analyzed. We recovered four isolates of EPNs (Heterorhabditis spp.) from the vicinity of Bakersfield, Blythe and Mecca, CA. Significant variation among soil types and soil depths in the EPNs’ ability to infect hosts was found. We also found significant correlations (using multiple linear regressions) between soil particle size, physical characteristics and the EPN foraging efficacy.