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

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.

Potential of two indigenous strains of entomopathogenic nematodes, (Steinernema feltiae and Heterorhabditis bacteriophora) against the tomato leafminer (TLM), Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), under laboratory and greenhouse environmental bioassay

“…The ability of EPNs to reach and kill T. absoluta larvae in leaf galleries was also reported (Batalla-Carrera et al, 2010;Van Damme et al, 2016;Kamali et al, 2018). The local EPN isolates were able to kill T. absoluta and had even been found to be effective against white grubs in Rwanda (Kajuga et al, 2018;Ndereyimana et al, 2019), while it was not easy to nd EPNs which can kill them (Laznik et al, 2015). Although EPNs live naturally in soil, different researchers found that they can be used on above-ground parts of the plant to control effectively the pests living in cryptic habitats like in leaf galleries (Batalla-Carrera et al, 2010;Garcia-del-Pino et al, 2013;Lankin et al, 2021), which concurs with the results of the present study under laboratory conditions.…”

Potential of two indigenous strains of entomopathogenic nematodes, (Steinernema feltiae and Heterorhabditis bacteriophora) against the tomato leafminer (TLM), Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), under laboratory and greenhouse environmental bioassay

“…The ability of EPNs to reach and kill T. absoluta larvae in leaf galleries was also reported (Batalla-Carrera et al, 2010;Van Damme et al, 2016;Kamali et al, 2018). The local EPN isolates were able to kill T. absoluta and had even been found to be effective against white grubs in Rwanda (Kajuga et al, 2018;Ndereyimana et al, 2019), while it was not easy to nd EPNs which can kill them (Laznik et al, 2015). Although EPNs live naturally in soil, different researchers found that they can be used on above-ground parts of the plant to control effectively the pests living in cryptic habitats like in leaf galleries (Batalla-Carrera et al, 2010;Garcia-del-Pino et al, 2013;Lankin et al, 2021), which concurs with the results of the present study under laboratory conditions.…”

“…More than 100 species of EPNs have been identi ed worldwide (about 80% by steinernematid) and at least 13 of these species have been marketed (Shapiro-Ilan et al, 2014;Ndereyimana et al, 2019). In general, the natural violence against various insect species varies between EPN species.…”

Entomopathogenic nematodes associated with organic honeybush (Cyclopia spp.) cultivation in South Africa

“…This is crucial in the fight against impending food crisis, combating hunger and promoting food security in the continent. For instance, the biocontrol efficacy of a native EPN species was demonstrated against the devastating tomato leaf miner, Tuta absoluta Meyrick Lepidoptera: Gelechiidae, which was reported as a serious pest against tomato production in many African countries (Ndereyimana et al, 2019;Dlamini et al, 2020). It is therefore important to identify species that are adaptable to existing IPM systems, well suited to native environmental conditions, and which could be mass-produced for industrial and commercial purposes.…”