Towards an understanding of the mechanisms of tolerance: compensating for herbivore damage by enhancing a mutualism

Abstract.   1. Traditionally, losses in plant fitness or yield resulting from insect damage have been redressed by reducing pest populations using insecticides or biocontrol; these approaches rely on the untested assumption that reduced plant fitness or yield is caused by diminished resources available to damaged plants.
2. By experimentally manipulating pollination and damage levels independently, it is shown that pollination, as well as lack of resources, may be limiting to damaged plants in a model insect-pollinated crop, cantaloupe.
3. With enhanced pollination, damaged plants produce as much fruit as undamaged plants, even under high damage levels. In contrast, damaged plants without supplemental pollination produced significantly less fruit than undamaged plants.
4. This approach is unique in shifting the focus away from reducing pest populations and toward enhancing mutualistic interactions. It avoids risks posed by insecticides (which also kill pollinators) and by biocontrol agents, known threats to native species.
5. Determining the mechanism underlying compensation sheds light on recovery from insect damage in both natural and managed systems. These results have a bearing on managing native plant populations suffering from pollinator declines.
6. Finally, it may be predicted that resources could limit tolerance to herbivore damage in resource-poor or high competition environments, whereas pollination may limit tolerance when resource levels are high.