Inbreeding in horsenettle influences herbivore resistance

1. Plant traits (e.g. nutrition, allelochemistry) are an important determinant of the feeding preferences and performance of insect herbivores. Recent evidence suggests that plant inbreeding can affect plant-insect interactions by impacting host-plant quality and resistance to herbivory. 2. The effect of inbreeding on host-plant quality for, and resistance against, the tobacco hornworm, Manduca sexta L., was assessed in the wild solanaceous weed horsenettle, Solanum carolinense L. Caterpillar preference, relative growth rate (RGR), total leaf consumption (TC), and per cent total nitrogen in leaves were examined using selfed and outcrossed progeny of eight maternal plants. 3. Inbreeding significantly influenced insect preference, with caterpillars preferring leaf discs from selfed versus outcrossed plants. There was also a breeding effect for RGR and TC, with both higher on selfed plants. No breeding effect for per cent total nitrogen was observed. 4. The results of this study indicate that inbreeding decreased resistance against the tobacco hornworm, but did not affect plant quality. Decreased plant resistance will likely alter interactions with the herbivore community and could also have important consequences for plant-herbivore-natural enemy interactions.