Viability and Virulence of Entomopathogenic Nematodes Exposed to Ultraviolet Radiation

摘要

Entomopathogenic nematodes (EPNs) can be highly effective biocontrol agents, but their efficacy can be reduced due to exposure to environmental stress such as from ultraviolet (UV) radiation.Our objectives were to 1) compare UV tolerance among a broad array of EPN species, and 2) investigate the relationship between reduced nematode viability (after exposure to UV) and virulence.Nematodes exposed to a UVradiation (254 nm) for 10 or 20 min were assessed separately for viability (survival) andvirulence to Galleria mellonella.We compared 9 different EPN species and 15 strains: Heterorhabditis bacteriophora (Baine, fl11, Oswego, and Vs strains), H.floridensis (332), H.georgiana (Kesha),H.indica (HOM1),H.megidis (UK211),Steinernema carpocapsae (All, Cxrd, DD136, and Sal strains), S.feltiae (SN), S.rarum (17CE), and S.riobrave (355).In viability assessments, steinernematids, particularly strains of S.carpocapsae, generally exhibited superior UV tolerance compared with the heterorhabditids.However, some heterorhabditids tended to be more tolerant than others, e.g., H.megidis and H.bacteriophora (Baine) were most susceptible and H.bacteriophora (Vs) was the only heterorhabditidthatdidnotexhibitasignificanteffectafter10minofexposure.Allheterorhabditidsexperiencedreducedviabilityafter 20minexposurethoughseveral S.carpocapsaestrainsdidnot.Intotal,after10or20minexposure,theviabilityofsevennematodestrains didnotdiffer fromtheirnon-UVexposedcontrols.Invirulenceassays,steinernematids(particularlyS.carpocapsaestrains)alsotendedto exhibit higher UV tolerance.However, in contrast to the viability measurements, all nematodes experienced a reduction in virulence relative to their controls.Correlation analysis revealed that viability among nematode strains is not necessarily related to virulence.In conclusion,our results indicatethat the impact of UVvaries substantially amongEPNs,andviabilityaloneis not a sufficient measurefor potential impact on biocontrol efficacy as other characters such as virulence may be severely affected even when viability remains high.