Three secondary metabolites (SMs) trans-cinnamic acid (TCA), (4E)-5-phenylpent-4-enoic acid (PPA), and indole derived from Photorhabdus bacterial symbionts of the entomopathogenic Heterorhabditis sonorensis (HS) nematode are known to have nematicidal and/or nematistatic activities against selected plant-parasitic nematodes. In this study we tested the effect of these SMs on the native nematode host (HS) and two additional non-target entomopathogenic nematodes, H. bacteriophora (HB) and Steinernema carpocapsae (SC). Specifically, we measured the effect of SMs on their virulence and reproductive fitness. Virulence was assessed as the ability of infective juvenile nematodes (IJs) to kill an insect host (insect mortality percentage) at five-day post-infection. Reproductive fitness was measured as the ability of the nematodes to reproduce in the insect host and produce progeny (measured as time to emergence and total IJ progeny after three-day post-initial emergence). Our results demonstrated that, for HS and SC, insect mortality and progeny emergence time were not affected by the tested SMs. Contrastingly, HB-IJs exposed to TCA exhibited significantly lower mortality and significant delay in progeny emergence when compared to the controls and the other tested SMs. With respect to progeny production, TCA and indole significantly reduced HS progeny, whereas PPA exerted a significant increase in IJ progeny for HB. Importantly, HB-IJs exposed to TCA showed the statistically similar progeny production to the control. With respect to SC, none of the tested SMs affected its reproductive fitness. Our results indicate that the EPNs exposed to TCA, PPA, and indole sustain their functional fitness.
.png)
