Variation in budbreak phenology affects the distribution of a leafmining beetle (Brachys tessellatus) on turkey oak (Quercus laevis)

Variation in plant phenology may be a major determinant of the distribution of herbivores on their host plants. We describe a field study in which we examined the consequences of budbreak phenology for densities of a leafmining beetle, Brachys tessellatus, on turkey oak, Quercus laevis. Budbreak phenology varies both within and among populations of Q. laevis in South Carolina. This variation appears to reflect mostly environmental variation within and among populations of trees, mediated in part by topography; larger trees and higher elevation trees broke bud earlier than smaller and lower elevation trees. Q. laevis that broke bud earlier suffered more leaf area loss to adult herbivory by B. tessellalus than trees that broke bud later; early-breaking trees lost as much as 15-20% leaf area to adult B. tessellatus feeding, while later-breaking trees generally lost < 5%. The effect of phenology on larval densities was more complicated; early-breaking trees accumulated more eggs than later-breaking trees early in the season. However, this relationship disappeared by mid-summer and there was no relationship between tree phenology and final numbers of mines or miners on trees at the end of the season. Thus, the consequences of variation in tree phenology for B. tessellatus abundance and herbivory on Q. laevis depend on the life history stage of the insect examined. This variable response to phenology by B. tessellatus reflects the patterns reported in other studies; insects primarily attacking young foliage and active early in the season are sensitive to phenological variation among plants, while herbivores primarily attacking mature foliage later in the season are not.