Plant wound compounds from oviposition scars used in host discrimination by a stem-galling sawfly

The stem-galling sawfly Euura lasiolepis uses one or more plant wound compounds resulting from oviposition scars as cues in host discrimination (avoiding sites occupied by conspecifics). Four experiments were conducted to test hypotheses about how Euura partitions resources. Experiment 1 demonstrated that Euura avoids ovipositing on nodes with scars from previous ovipositions. Experiment 2 showed no evidence that the sawfly uses oviposition-deterring pheromones and indicated there is a time lag following oviposition before the oviposition scar becomes a deterrent. Experiment 3 showed that sawflies avoid artificially formed scars, demonstrating that a plant cue alone can lead to host discrimination. Experiment 4 showed that visual or tactile cues are not necessary for host discrimination and indicated that a plant wound compound functions as an oviposition deterrent. Both experimental results and field surveys showed that Euura oviposition scars were more uniformly distributed than expected if sawflies were ignoring previous ovipositions.