Potential of entomopathogenic nematode isolates from Rwanda to control the tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

Assinapol Ndereyimana,Patrick Murerwa,Samuel Nyalala,Svetlana Gaidashova

doi:10.1186/s41938-019-0163-3

Assinapol Ndereyimana, Patrick Murerwa + Show 2 more

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https://doi.org/10.1186/s41938-019-0163-3

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Abstract

Tomato leaf miner, Tuta absoluta (Meyrick), is a major threat to tomato production as it can cause up to 100% yield loss under both greenhouse and open-field conditions. Chemical control, which is associated with several undesirable effects, remains the only option readily available for this pest since its invasion of Rwanda in the year 2015. This study assessed the potential of using local isolates of entomopathogenic nematodes (EPNs) in management of T. absoluta in Rwanda. Six EPNs including four locally isolated strains: Steinernema sp. RW14-M-C2a-3, Steinernema sp. RW14-M-C2b-1, S. carpocapsae RW14-G-R3a-2 and Heterorhabditis bacteriophora RW14-N-C4a, and two exotic species: S. carpocapsae All and H. bacteriophora H06 were evaluated. Three bioassays were conducted in the laboratory, using a tomato leaflet with third instar T. absoluta larva in gallery and 9-cm Petri dishes as bioassay arenas in a completely randomized design with three replications. The EPNs were applied at a volume of 1 ml containing 500 infective juveniles per leaflet, while sterile tap water was used as negative control. Larval mortality was checked continuously for 96 h at 24 h interval. The results revealed that all the tested EPNs were able to find and kill T. absoluta larvae inside the leaf galleries; and their efficacy increased with exposure time. The pathogenicity effects were significantly different (p < 0.05) among EPNs. In the first 24 h after inoculation, the efficacy of local EPN isolates (53.3–96.7%) was significantly higher than the one of exotic species (0.0–26.7%). The efficacy of three Rwandan EPN isolates, Steinernema sp. RW14-M-C2a-3, Steinernema sp. RW14-M-C2b-1, and S. carpocapsae RW14-G-R3a-2 was not significantly different from 24 to 96 h after inoculation, except for S. carpocapsae RW14-G-R3a-2 during 24 h after inoculation in bioassay 3. There was insignificant difference among all the EPN isolates after 96 h of exposure. This is the first study carried out in Rwanda that investigated the potential of locally isolated EPNs against T. absoluta. Field experiments should be conducted to fully explore the possibilities of using local EPN isolates in integrated pest management of T. absoluta in Rwanda.

Highlights

Tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is an invasive pest originating from South America and was detected for the first time in Rwanda in the year 2015 (FAO, 2015)
Source and mass production of Entomopathogenic nematodes (EPN) Six EPNs including four local isolates and two exotic species, maintained in the Biological Control Laboratory—EPN Production Facility of Rwanda Agriculture and Animal Resources Development Board (RAB) were used for the study
All EPN isolates evaluated were able to find, infect, and kill T. absoluta larvae inside the tomato leaf galleries, with different levels of pathogenicity (Table 1)

Summary

Introduction

Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is an invasive pest originating from South America and was detected for the first time in Rwanda in the year 2015 (FAO, 2015) This pest is the major threat to tomato production as it can cause up to 100% yield loss under both greenhouse and open-field conditions (Desneux et al, 2010 and Biondi et al, 2018). The short developmental period of this pest and its many generations per year lead to numerous insecticide sprays in one season (Biondi et al 2018) This facilitates the development of resistant pest strains to frequently used insecticides (Haddi et al 2017) and leads to the destruction of natural enemies (Macharia et al 2009). The limited effectiveness in addition to hazardous nature of chemical insecticides (Macharia et al 2009), trigger the need for integrated pest management (IPM) and use of pest control actions that assure positive economic, ecological, and sociological effects (Blake et al 2007)

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