Fig. 4

Heterorhabditis bacteriophora exhibits age-dependent changes in olfactory behavior. a Infective juveniles (IJs) were grown at 25 °C and temperature-swapped to 15 °C on day 0. The olfactory responses of temperature-swapped day 28 IJs but not day 14 IJs were significantly different from those of 25 °C day 0 IJs for all odorants except methyl salicylate and CO₂. * P < 0.05; *** P < 0.001 relative to day 0 IJs; two-way ANOVA with Dunnett’s post-test; n = 6–8 trials for each condition. b IJs were grown and maintained at 25 °C. Olfactory responses to all odorants except CO₂ changed as a function of parasite age. * P < 0.05; ** P < 0.01; *** P < 0.001 relative to day 0 IJs; two-way ANOVA with Dunnett’s post-test; n = 6–8 trials for each condition. c, d IJs were grown at 25 °C and either temperature-swapped to 15 °C and back to 25 °C (c) or maintained at 25 °C (d). IJs were then tested for their responses to benzaldehyde and 1-hexanol, which showed the largest valence change in (b). In both conditions, IJs switched their odorant response from attraction to repulsion over time, consistent with an age-dependent effect. *** P < 0.001 relative to day 0 IJs; two-way ANOVA with Dunnett’s post-test; n = 8 trials for each condition. For all graphs, error bars represent standard error of the mean (SEM). Mean, n, and SEM values for each assay are listed in Additional file 7: Dataset S1