Characterization and Pathogenicity Test of Entomopathogenic Nematode Steinernema Species-Kalro

C N Ngugi,D K Sirengo,H M Mburu,P M Wachira,S Okoth,J N Mbaka,S Haukeland,M Adhiambo

doi:10.5539/jas.v13n3p93

Abstract

Entomopathogenic nematodes (EPNs) are worldwide soil-dwelling insect parasitic nematodes. They are potential pest bio-control agents a key component of Integrated Pest Management (IPM) programs. This study aimed to characterize and evaluate the pathogenicity of an EPN isolate from Kenya. The nematode was isolated from soils using insect bait technique and both morphological and molecular identification was performed. Efficacy of the isolate was evaluated against Tomato leafminer larvae (Tuta absoluta Meyrick.) using dose-based treatments of 0-control, 100, 150, 200, and 250 infective juveniles (IJs/ml). Morphological analysis revealed body length (L) of 835(659-987) &micro;m and 1781 (1297-2097) &micro;m from fresh IJs and males respectively. Males lacked a mucron. The isolate was characterized by the partial sequence length of 877 bp of the ITS region. Blastn results indicated the EPN isolate had a similarity match of 81-92% with Afro-tropical Steinernema species. It matched with Steinernema sp. (AY230186.1) from Kenya at 92% and Sri Lanka (AY230184.1). Phylogenetic analysis placed the isolate together with Steinernema sp. (AY230186.1) and (AY230184.1) with a bootstrap value of 100%. Maximum mean larval mortality (80%; 96%) was achieved 24 and 48 h post-treatment at concentration 150 IJs/ml. All nematode concentrations achieved over 50% mean mortality after 24 h period. There was a significant difference (P = 0.001) between doses 150 and 200 IJs/ml. From the study, it was concluded that the nematode isolate was Steinernema sp now referred to as Steinernema sp. Kalro (Genebank Accession MW151701). The EPN has the potential for development as a biological control agent against T. absoluta.

Highlights

Entomopathogenic nematodes (EPNs) in the families’ Steinernematidae and Heterorhabditidae are pathogenic to insects (Kalia et al, 2014; Gozel & Kasp, 2015; de Brida et al, 2017), found in most soils worldwide
The EPN isolate was isolated from soils at Kenya Agricultural and Livestock Research Organisation (KALRO)-Thika and reared using the insect-baiting method as described by (Bedding & Akhurst, 1975)
Most of the “feltiae” group members are found in the “glaseri” group including relatives of nematode isolate; the Steinernema karii (Kenya), S. pwaniensis (Tanzania), S. ethiopense (Ethiopia), and S. jeffreynse (South Africa) all from Africa (Waturu et al, 1998; Malan et al, 2016; Puza et al, 2015)

Summary

Introduction

Entomopathogenic nematodes (EPNs) in the families’ Steinernematidae and Heterorhabditidae are pathogenic to insects (Kalia et al, 2014; Gozel & Kasp, 2015; de Brida et al, 2017), found in most soils worldwide. The released bacteria provide pathogenicity, degrade and breakdown host tissue, and suppress the immunity of the host. These bacteria are known to produce toxic proteins (metabolites) that render EPNs lethal to insect hosts. The mutualism of bacteria and nematodes is vital as it inhibits the development of resistance in the host insect The nematodes complete their lifecycle within the host insect after which they exit into the soil and lie in wait for another suitable host (Poinar Jr., & Grewal, 2012; Sternberg & Dillman, 2012; Kalia et al, 2014; Gozel & Kasap, 2015)

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