1. Induced plant responses to herbivory are common and we have learned a lot about the mechanisms of induced resistance and their effects on herbivore performance.  We know less about their effects on herbivore behavior and especially on spatial patterns of damage.

2. Theoretical models predict that induced responses can cause patterns of damage to become aggregated, random, or even.  A recent model predicted that informed herbivore movement coupled with communication between plants would make damage more even within individual plants.  We tested these predictions in the field using a specialist beetle (Trirhabda pilosa) that feeds on sagebrush (Artemisia tridentata). Both the beetle and the plant are well-documented to respond to damage-induced volatile cues.

3. Beetle larvae were more likely to move from damaged leaves and leaves that had been exposed to volatiles from nearby damaged leaves compared to undamaged control leaves.  Previous lab results indicated that beetles were more likely to choose undamaged leaves compared to damaged leaves or those exposed to volatile cues of damage.

4. A comparison of damage patterns early in the season and after completion of beetle feeding revealed that variance in damage among branches decreased as the season progressed; i.e., damage became more evenly distributed among the branches within a plant.  Larvae damaged many leaves on a plant but removed relatively little tissue from each leaf.

5. Herbivore movement and the spatial patterns of damage that it creates can be important in determining effects on plant fitness and other population processes.  Dispersion of damage deserves more consideration in plant-herbivore studies.

Data for figure 1 are in the file sagebeetledam.xlsx

Data for figure 5 are in the file Distribution_of _damage_10_bushes.xlsx, sheet 2. Jdam in column C is the number of leaves that had damage during the July survey. Jtot in column D is the total number of leaves on each branch during the July survey. Adam in column E is the number of leaves that had damage during the August survey. Atot in column G is the total number of leaves on each branch during the August survey. Prodam in columns G, H is the proportion of leaves with damage during July and August respectively.