Settling on leaves or flowers: herbivore feeding site determines the outcome of indirect interactions between herbivores and pollinators

Herbivore attack can alter plant interactions with pollinators, ranging from reduced to enhanced pollinator visitation. The direction and strength of effects of herbivory on pollinator visitation could be contingent on the type of plant tissue or organ attacked by herbivores, but this has seldom been tested experimentally. We investigated the effect of variation in feeding site of herbivorous insects on the visitation by insect pollinators on flowering Brassica nigra plants. We placed herbivores on either leaves or flowers, and recorded the responses of two pollinator species when visiting flowers. Our results show that variation in herbivore feeding site has profound impact on the outcome of herbivore-pollinator interactions. Herbivores feeding on flowers had consistent positive effects on pollinator visitation, whereas herbivores feeding on leaves did not. Herbivores themselves preferred to feed on flowers, and mostly performed best on flowers. We conclude that herbivore feeding site choice can profoundly affect herbivore-pollinator interactions and feeding site thereby makes for an important herbivore trait that can determine the linkage between antagonistic and mutualistic networks.