Activity of Steinernema colombiense in plant-based oils.

Gabriela Castruita-Esparza,Francisco Ángel Bueno-Pallero,Lídia Dionísio,Teodulfo Aquino-Bolaños,Raquel Campos-Herrera,Rubén Blanco-Pérez

doi:10.21307/jofnem-2020-072

Abstract

Entomopathogenic nematodes (EPNs) are excellent biological control agents. Although traditionally EPN application targeted belowground insects, their aboveground use can be supported if combined with adjuvants. We hypothesized that EPN infective juveniles (IJs) could be combined with plant-based oils as adjuvants, without decreasing their efficacy against insect larvae under various scenarios. Specifically, our objectives were to evaluate the activity of Steinernema colombiense (Nematoda: Steinernematidae) when mixed with two plant-based oils (coconut and olive oils) and maintained at different temperatures and times, or combined with entomopathogenic fungi. First, we evaluated how these oils affected IJ survival and virulence against last instar Galleria mellonella (Lepidoptera: Pyralidae) larvae when maintained at five different temperatures (4, 8, 14, 20, and 24°C) and five incubation times (1, 3, 7, 14, and 21 days), using water as control treatment. Second, we evaluated virulence when combined with these two oils as well as with water (control) and combined with the entomopathogenic fungi (EPF), Beauveria bassiana (Hypocreales: Clavicipitaceae). Infective juvenile survival was higher in coconut than olive oil and water mixtures up to 7 days at 4°C. Conversely, olive oil supported higher larval mortality than coconut oil at 4 to 20°C and 14 days. Similarly, the number of days needed to kill insect larvae increased at extreme temperatures (4 and 24°C) after 14 days. Finally, the EPN + EPF combination showed an additive effect compared to EPN and EPF single treatments. Our findings indicate that our plant-based oil mixtures maintain viable IJs at moderate temperatures and up to 7 to 14 days, and can be used in single EPN mixtures or combined with EPF.

Highlights

Their worldwide distribution in soils (Kaya et al, 2006) and the availability of commercial products (Lacey et al, 2015) make the Entomopathogenic nematodes (EPNs) excellent agents to employ them in integrated pest management (IPM) programs and under organic production (CamposHerrera, 2015)
For example, since certain plant-based oils such as coconut oil remain solid at relative high temperatures (~24°C), this could be of interest for producing stable shipments
We performed an Impact of temperature and time on the survival and virulence of the entomopathogenic nematode combined with plant-based oils

Summary

Introduction

Their worldwide distribution in soils (Kaya et al, 2006) and the availability of commercial products (Lacey et al, 2015) make the EPNs excellent agents to employ them in integrated pest management (IPM) programs and under organic production (CamposHerrera, 2015). The most widespread practice for EPNs use in biocontrol agent is the massive application of infective juveniles (IJs) stages in belowground agroecosystems, where they are naturally adapted (Lacey et al, 2015) Numerous substrates such as vermiculite, clay, activated charcoal, polyacrylamide, alginate capsules, or simple water-dispersible granules have been tested as formulation agents with variable shelf life and storage limitations (Hiltpold, 2015; Ramakuwela et al, 2015; Kary et al, 2018; Leite et al, 2018; Touray et al, 2020). Previous studies have reported successful co-applications with entomopathogenic fungi (EPF), arbuscular mycorrhizal soil fungi, and bacteria in the genus Pseudomonas (Shapiro-Ilan et al, 2004; Molina-Acevedo et al, 2007; Ansari et al, 2008; Imperiali et al, 2017; Jaffuel et al, 2019) This co-application approach is a promising tool for sustainable agriculture that, once optimized, could save costs and time to growers. The EPF Beauveria bassiana (Hypocreales: Clavicipitaceae), which occurs in natural and agricultural soils worldwide, is one of the most prominent biological control agents used among commercial products (Lacey et al, 2015), and can be an excellent candidate for combinations of this kind

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