Identification of entomopathogenic nematodes and their symbiotic bacteria in national parks of Thailand, and mosquitocidal activity of Xenorhabdus griffiniae against Aedes aegypti larvae

Abstract

Summary Entomopathogenic nematodes (EPN) Steinernema and Heterorhabditis with symbionts with Xenorhabdus and Photorhabdus bacteria, respectively, are reported as biocontrol agents for insect control. The objectives of this study were to identify EPN and their symbiotic bacteria in national parks of Phitsanulok Province, Thailand, and to test how Xenorhabdus isolates attack Aedes aegypti larvae. We collected 810 soil samples from four national parks. The juvenile stage of EPN was isolated from soil samples using a baiting technique with Galleria mellonella followed by a White trap. Partial regions of 28S rDNA and internal transcript spacer were sequenced to identify EPN, and recA sequencing was used to discriminate between Xenorhabdus and Photorhabdus. We found that 74 of the 810 soil samples (9.1%) were positive for the EPN. The EPN were molecularly identified as S. surkhetense, S. longicaudum, H. indica and Heterorhabditis sp. SGmg3, and their symbiotic bacteria were identified as X. stockiae, X. griffiniae, X. indica, X. vietnamensis, P. luminescens subsp. akhurstii, and P. temperata subsp. temperata. Xenorhabdus griffiniae showed potential larvicidal activity against A. aegypti (91% mortality at 72 and 96 h after exposure). This study demonstrates the diversity of EPN and symbiotic bacteria in national parks of Thailand and the potential to use X. griffiniae as a biocontrol agent to kill A. aegypti larvae.

Entomopathogenic Nematodes and Their Symbiotic Bacteria from the National Parks of Thailand and Larvicidal Property of Symbiotic Bacteria against Aedes aegypti and Culex quinquefasciatus

“…This diversity is due, at least in part, to a large number of different insect host species that coexist in Thailand’s national parks. The prevalence of EPNs isolated from soil samples in national parks of Thailand are variable, ranging from 2.87% in Nam Nao National Park [ 19 ], 4.36% in Mae Wong National Park [ 18 ], 9.1% in four national parks of Phitsanulok Province [ 20 ] to 9.5% in the present study. The presence of EPNs in the surveyed areas is influenced by several factors.…”

“…This survey recorded H. zealandica and S. kushidai for the first time in the country [ 18 ]. Yooyangket et al reported the finding of H. baujardi and S. websteri in Nam Nao National Park, Phetchabun Province [ 19 ], while, most recently, S. longicuadum was isolated from soil samples in Kaeng Chet Khwae National Park in Phitsanulok Province, Thailand [ 20 ]. In the present study, H. indica , H. baujardi , Heterorhabditis SGmg3, S. guangdongense , S. surkhetense , and S. minutum were isolated from soil samples in Kaeng Krachan National Park, Phetchaburi Province, Namtok Samlan National Park, Saraburi Province, Phu Phan National Park, Sakhon Nakhon Province and Huai Nam Dang National Park, Chiang Mai Province, Thailand.…”

“…This was followed by the identification of numerous species found in one study included S. websteri , S. khoisanae , H. indica , H. bacteri-ophora and H. baujardi [ 15 ], and subsequently, S. websteri reported from lower northern Thailand [ 16 , 17 ]. At present, 15 EPN species representing a variety of ecological soil types in different geographic regions of Thailand have been reported including, S. siamkayai , S. surkhetense , S. websteri (synonym S. carpocapsae ), S. scarabiae , S. kushidai , S. minutum , S. khoisanae , S. longicaudum , S. guangdongense , S. huense , S. sangi , H. indica (synonym H. gerrardi ), H. baujardi (synonym H. somsookae ), H. bacteiophora and H. zealandica [ 15 , 17 , 18 , 19 , 20 , 28 , 35 , 36 , 38 , 39 , 40 , 41 ]. In addition, three Steinernema isolates ( Steinernema sp.…”

“…namnaonensis and P. temperata subsp. temperata [ 18 , 19 , 20 , 28 , 38 , 40 , 43 ]. Recently, Photorhabdus australis subsp.…”

“…The previously studied locations for surveying EPNs and symbiotic bacteria in Thai-land included roadside verges, areas of fruit crops, field crops, rice fields, and the banks of rivers and ponds [ 14 , 15 , 16 , 17 ], and typically have yielded low prevalence (<10%) and species diversity (<10 species) of EPNs and symbiotic bacteria. Surveys of EPNs and symbiotic bacteria in the national parks have resulted in several new records in Thailand [ 18 , 19 , 20 ]. In addition, at least two new species of EPNs were isolated from national parks in Vietnam [ 21 , 22 ].…”