Identification of entomopathogenic nematodes and symbiotic bacteria from Nam Nao National Park in Thailand and larvicidal activity of symbiotic bacteria against Aedes aegypti and Aedes albopictus

Abstract

Entomopathogenic nematodes (EPNs) that are symbiotically associated with Xenorhabdus and Photorhabdus bacteria can kill target insects via direct infection and toxin action. There are limited reports identifying such organisms in the National Park of Thailand. Therefore, the objectives of this study were to identify EPNs and symbiotic bacteria from Nam Nao National Park, Phetchabun Province, Thailand and to evaluate the larvicidal activity of bacteria against Aedes aegypti and Ae. albopictus. A total of 12 EPN isolates belonging to Steinernema and Heterorhabditis were obtained form 940 soil samples between February 2014 and July 2016. EPNs were molecularly identified as S. websteri (10 isolates) and H. baujardi (2 isolates). Symbiotic bacteria were isolated from EPNs and molecularly identified as P. luminescens subsp. akhurstii (13 isolates), X. stockiae (11 isolates), X. vietnamensis (2 isolates) and X. japonica (1 isolate). For the bioassay, bacterial suspensions were evaluated for toxicity against third to early fourth instar larvae of Aedes spp. The larvae of both Aedes species were orally susceptible to symbiotic bacteria. The highest larval mortality of Ae. aegypti was 99% after exposure to X. stockiae (bNN112.3_TH) at 96 h, and the highest mortality of Ae. albopictus was 98% after exposure to P. luminescens subsp. akhurstii (bNN121.4_TH) at 96 h. In contrast to the control groups (Escherichia coli and distilled water), the mortality rate of both mosquito larvae ranged between 0 and 7% at 72 h. Here, we report the first observation of X. vietnamensis in Thailand. Additionally, we report the first observation of P. luminescens subsp. akhurstii associated with H. baujardi in Thailand. X. stockiae has potential to be a biocontrol agent for mosquitoes. This investigation provides a survey of the basic diversity of EPNs and symbiotic bacteria in the National Park of Thailand, and it is a bacterial resource for further studies of bioactive compounds.

Survey of entomopathogenic nematodes and associate bacteria in Thailand and their potential to control Aedes aegypti

“…In Thailand, X. stockiae has been reported as a potential organism for controlling Aedes spp. (Yooyangket et al, ), cow mastitis‐causing bacteria (Bussaman & Rattanasena, ) and mushroom mites (Namsena, Bussaman, & Rattanasena, ). These data indicate that X. stockiae may be a natural biological control agent.…”

“…albopictus larvae were susceptible to symbiotic bacteria, with high mortality after exposure to P. luminescens , X. nematophila (da Silva et al, ), X. stockiae (bNBP22.2_TH), X. indica (bKK26.2_TH) (Vitta et al, ), X. ehlersii bMH9.2_TH, X. stockiae (bLPA18.4_TH) (Fukruksa et al, ), X. stockiae (bNN112.3_TH), and P. luminescens subsp. akhurstii (bNN121.4_TH) (Yooyangket et al, ). These symbiotic bacteria could produce secondary metabolites that acted as insecticidal compounds (Cai et al, ; Dreyer, Malan, & Dicks, ).…”

“…aegypti was used for screening method. Mosquito rearing protocols and larvicidal tests were described previously (Yooyangket et al, 2018).…”

“…Thailand, 12 species of EPNs and seven species of bacteria associated with these EPNs have been found in several regions Muangpat et al, 2017;Thanwisai et al, 2012;Yooyangket et al, 2018). In earlier studies on the diversity of EPNs and symbiotic bacteria, the common symbiotic relationship between Steinernema and Xenorhabdus was found to be S. websteri associated with X. stockiae, whereas a mutual relationship was found between Heterorhabditis and Photorhabdus (H. indica associated with P. luminescens subsp.…”

“…Cell suspensions of Xenorhabdus and Photorhabdus have also been reported as biocontrol agents against Aedes spp. in the laboratory (Da Silva et al, ; Fukruksa et al, ; Vitta et al, ; Yooyangket et al, ). Therefore, Xenorhabdus and Photorhabdus are interesting alternative larvicides for controlling Aedes mosquitoes.…”