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Title: Viability and virulence of entomopathogenic nematodes exposed to ultraviolet radiation

item Shapiro Ilan, David
item HAZIR, SELCUK - Adnan Mederes University
item LEITE, LUIS - Instituto Biologicio - Brazil

Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2015
Publication Date: 10/1/2015
Citation: Shapiro-Ilan, D.I., Hazir, S., Leite, L. 2015. Viability and virulence of entomopathogenic nematodes exposed to ultraviolet radiation. Journal of Nematology. 47(3):184–189.

Interpretive Summary: Entomopathogenic nematodes, also known as beneficial nematodes, are environmentally friendly bio-insecticides that are used to control a wide variety of economically important insect pests. The efficacy of these nematodes in biological pest control can be reduced due to various environmental stresses, such as ultra violet radiation (UV) that is emitted by sunlight. Therefore, when choosing which nematode species to use for a biological control application, it may be important to consider which nematode is most tolerant to UV. However, prior to our study only a few nematode species or strains were tested for UV tolerance. Our objective was to compare UV tolerance among a broad array of nematode species. We compared 9 different nematode species and 15 strains. Overall, we observed substantial variation in UV tolerance, and a species called Steinernema carpocapsae was deemed to be most tolerant. We also discovered that many nematode species that remained alive after exposure to UV were unable to infect and kill insect pests. Thus, our research indicates that companies and laboratories that are assessing the quality and fitness of entomopathogenic nematodes need to consider both nematode virulence (killing power) as well as viability (survival).

Technical Abstract: Entomopathogenic nematodes can be highly effective biocontrol agents, but their efficacy can be reduced due to exposure environmental stress such as from ultraviolet radiation. Our objective was to compare UV tolerance among a broad array of nematode species. 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 (17C&E), and S. riobrave (355). For viability assessments, steinernematids, particularly strains of S. carpocapsae, generally exhibited superior UV tolerance compared with the heterorhabditids, yet some heterorhabditids were more tolerant than others, e.g., H. megidis and H. bacteriophora (Baine) were most susceptible and H. bacteriophora (Vs) was the only heterorhabditid that did not exhibit a significant effect after 10 min of exposure. In total, after 10 or 20 min exposure, the viability of seven nematode strains did not differ from their non-UV exposed controls. In virulence assays, steinernematids (particularly S. carpocapsae strains) also tended to exhibit relatively 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 relative viability among nematode strains is not necessarily related to virulence. In conclusion, our results indicate that the impact of UV varies substantially among EPNs, and viability alone is not a sufficient measure for potential impact on biocontrol efficacy as other “hidden” characters such as virulence may be severely affected even when viability remains high.