Lagged effects of herbivory impact host‐choice but not nymphal survivorship in an ant‐protected treehopper

Abstract

Abstract Theoretical studies have shown that in protection mutualism, the modification of top‐down control by protectors may be destabilizing. Central to this prediction are the assumptions that (1) protection mutualism increases the abundance of protected partners, (2) this increased abundance generates a lagged effect on partner resources, and (3) spatial dynamics can be ignored. Although a number of studies have confirmed that protection mutualism can increase the abundance of protected herbivores, the evidence for a negative effect of protected herbivores on plant quality is mixed, and we are unaware of any studies that have explored the effect of protected herbivores on plant quality across growing seasons. Here, we use the protection mutualism between ants and the treehopper Publilia concava to evaluate the assumption that treehopper herbivory has a lagged effect on plant quality. We also evaluated whether ant protection exacerbated the negative effect of treehoppers on their host plants. We used a two‐way factorial design that manipulated ant and treehopper presence on goldenrod host plants in 1 year and assessed oviposition and survivorship on those same plants in the subsequent year. Treehopper herbivory was associated with a decrease in the probability of oviposition, and female treehoppers laid significantly fewer egg masses on plants that had been fed on the previous year, regardless of ant tending. In contrast, a prior history of herbivory had no impact on future treehopper performance as measured by nymph survival. Ant tending increased treehopper abundance and exacerbated the risk of plant mortality but otherwise did not significantly modify the negative effect of treehopper herbivory on plant quality or future treehopper performance. Although the increase in treehopper abundance associated with ant tending and the lagged oviposition response of treehoppers is consistent with the core assumptions of a model showing that mutualism can be destabilizing, the avoidance of previously occupied plants for oviposition is not. These results highlight the importance of future modeling studies that explore spatiotemporal dynamics in protection mutualism and long‐term field studies that track the effect of mutualism across years.

Keywords

• herbivory
• induced plant response
• mutualism
• oviposition
• preference–performance hypothesis
• Publilia concava