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Title: Characterization of biocontrol traits in Heterorhabditis floridensis: A species with broad temperature tolerance

item Shapiro Ilan, David
item BLACKBURN, DANA - Brigham Young University
item DUNCAN, LARRY - University Of Florida
item EL BORAI, FAHIEM - University Of Florida
item KOPPENHOFER, HEATHER - University Of Florida
item TAILLIEZ, PATRICK - University Of Montpellier
item ADAMS, BYRON - Brigham Young University

Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2014
Publication Date: 12/31/2014
Citation: Shapiro Ilan, D.I., Blackburn, D., Duncan, L., El Borai, F.E., Koppenhofer, H., Tailliez, P., Adams, B.J. 2014. Characterization of biocontrol traits in Heterorhabditis floridensis: A species with broad temperature tolerance. Journal of Nematology. 46:336–345.

Interpretive Summary: Beneficial insect-killing nematodes (also called entomopathogenic nematodes) are small round worms that are used as environmentally friendly bio-insecticides. These nematodes are applied to control many different kinds of insect pests and are safe to humans and other non-target organisms. Also, these nematodes kill their insect hosts with the help of a partner, a symbiotic bacterium that the nematodes carry with them. New species of beneficial nematodes are found every year; these new species may possess superior abilities compared with formerly known species. Therefore, when new nematode strains and species are found, it is important to characterize the new nematode’s potential to be used as a new biological insecticide. In this study, we investigated the traits and abilities of a previously uncharacterized species named Heterorhabditis floridensis. First, we identified the bacteria partner that lives in the nematode, it is called Photorhabdus luminescens luminescens. Next we tested the nematode for virulence (killing power) and found the new nematode was similar to many other species in that respect. However, we discovered that the new nematode (Heterorhabditis floridensis) possesses exception ability to withstand high temperatures, and the nematode can also infect insects at relatively low temperatures too. Therefore, the nematode species may be useful for natural insect control purposes in environments where temperature extremes occur within short durations.

Technical Abstract: Biological characteristics of two strains of the entomopathogenic nematode, Heterorhabditis floridensis (strain 332 isolated in Florida, and K22 isolated in Georgia, USA) were described. The identity of the nematode’s symbiotic bacteria was elucidated and found to be Photorhabdus luminescens luminescens. Subsequently, beneficial traits pertinent to biological control (i.e., environmental tolerance, reproduction, and virulence) were characterized. The range of temperature tolerance was found to be broad and show a high level of heat tolerance. The H. floridensis strains caused higher levels of mortality or infection in G. mellonella at 30 °C and 35 °C compared with S. riobrave (355), a strain widely known to be heat tolerant, and the H. floridensis strains were also capable of causing infection at 17 °C whereas S. riobrave (355) was not. However, at higher temperatures of 37 °C and 39 °C, though H. floridensis readily infected G. mellonella, S. riobrave strains (355, 7-12, and 9-5) caused higher levels of mortality. Desiccation tolerance in the H. floridensis strains was moderate. The virulence of H. floridensis to four insect pests (Aethina tumida, Conotrachelus nenuphar, Diaprepes abbreviatus, and Tenebrio molitor) was determined relative to seven other nematodes. Virulence to A. tumida was similar among the H. floridensis strains and most other nematodes. Only five nematode treatments caused higher mortality than the control in C. nenuphar: H. bacteriophora, H. indica, S. feltiae, and S. glaseri (4-8). All nematodes were pathogenic to D. abbreviatus though S. glaseri (4-8) and S. riobrave (355) were the most virulent. In summary, the H. floridensis strains possess a wide niche breath in temperature tolerance and have virulence and desiccation levels that are similar to a number of other entomopathogenic nematodes. The strains may be useful for biocontrol purposes in environments where temperature extremes occur within short durations.