Intraspecific virulence of entomopathogenic nematodes against the pests Frankliniella occidentalis (Thysanoptera: Thripidae) and Tuta absoluta (Lepidoptera: Gelechiidae).

Raquel Campos-Herrera,David Labarga,Javier Calvo,Miguel Puelles,Magda Galeano,José Eduardo Belda,Alicia Pou,Ignacio Vicente-Díez,Maryam Chelkha,María Del Mar González-Trujillo

doi:10.21307/jofnem-2021-102

Abstract

Entomopathogenic nematodes (EPN) are excellent biocontrol agents against various insect pests. Novel biotechnological approaches can enhance their utility against insects above-ground, opening a new venue for selecting superior EPN against certain insects. We hypothesize that different populations of the same species but from different origins (habitat, ecoregion) will differ in their virulence. This study aimed to evaluate the virulence of various EPN populations against two pests of worldwide incidence and damage to high value crops: Frankliniella occidentalis (Thysanoptera: Thripidae) and Tuta absoluta (Lepidoptera: Gelechiidae). We tested 10 EPN populations belonging to three EPN species: Heterorhabditis bacteriophora (Koppert, MG-618b, AM-203, RM-102), Steinernema feltiae (Koppert, RS-5, AM-25, RM-107), and Steinernema carpocapsae (Koppert, MG-596a). Each EPN population was tested at two concentrations. Frankliniella occidentalis was tested at 160 and 80 IJs/cm2 and T. absoluta at 21 and 4 IJs/cm2. Control treatments followed the same experimental procedure but only adding distilled water. Overall, whenever different, higher IJs concentration resulted in lower adult emergence, higher larval mortality, and shorter time to kill the insects. Considering the low concentration, S. feltiae provided the best results for both insects and instars investigated, while H. bacteriophora and S. carpocapsae required a high concentration to reach similar or slightly better results. Differences among populations of each of the species were detected, but only the native populations of H. bacteriophora populations showed consistently higher control values against both insects/instar compared with the commercial one. Differences among S. feltiae and S. carpocapsae populations depended on the IJs concentration, insect, and instar. We consider S. feltiae a very promising species for their application against F. occidentalis and T. absoluta, with the Koppert population as the most consistent among the populations tested. Specific EPN-populations of S. carpocapsae and H. bacteriophora were good candidates against certain instar/insects at high concentrations. This study emphasized the importance of intraspecific variability for EPN virulence.

Highlights

IntroductionEntomopathogenic nematodes (EPNs) in the gen era Steinernema and Heterorhabditis are excellent biocontrol agents against many arthropod species (Campos-Herrera, 2015; Lacey et al, 2015)
Entomopathogenic nematodes (EPNs) in the gen era Steinernema and Heterorhabditis are excellent biocontrol agents against many arthropod species (Campos-Herrera, 2015; Lacey et al, 2015). They are naturally distributed in the soil in the form of infective juvenile (IJ), which has to survive while searching for a Commons CC BY 4.0 license, https://creativecommons.org/licenses/by/4.0/
The EPN species differ for traits related to the ability to survive in the environment, to overcome predation or competition for resources, search for a host, kill, or reproduce (Campbell et al, 2003; Grewal et al, 2006; Griffin, 2015)

Summary

Introduction

Entomopathogenic nematodes (EPNs) in the gen era Steinernema and Heterorhabditis are excellent biocontrol agents against many arthropod species (Campos-Herrera, 2015; Lacey et al, 2015). Intraspecific variability in parameters related to reproductive capability and life cycles, virulence against the agricultural pests Ceratitis capitata (Diptera: Tephritidae) and Spodoptera littoralis (Lepidoptera: Noctuidae), and the physiology and molecular profile of their associated bacteria was described among several isolates of S. feltiae from various habitats from La Rioja (Northern Spain) (Campos-Herrera et al, 2007, 2008, 2009; CamposHerrera and Gutierrez, 2009, 2014). Another example of intraspecific variability was provided by Bruno et al (2020). We explored the intraspecific differences for each of the three EPN species using two concentrations of nematodes

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