The relationship between stem-galling wasps and mycorrhizal colonization of Quercus turbinella

While numerous studies have examined the relationship between herbivory and mycorrhizal colonization, few studies have been undertaken on plant species such as oaks that can be dually colonized by both arbuscular mycorrhizas (AM) and ectomycorrhizas (EM). We examined the relationship between insect herbivory by a stem-galling wasp (Cynipidae) and the mycorrhizal colonization of shrub live oaks (Quercus turbinella Greene). We found that oaks with high numbers of galls had 2.4 times higher levels of branch die-back and were 2.3 times more water stressed than oaks with low numbers of galls. Oaks with high numbers of galls supported 21% higher levels of AM colonization but had 53% lower levels of EM colonization than oaks with low numbers of galls. In addition, AM colonization was positively correlated with the number of galls per tree, while EM colonization was negatively correlated with the number of galls per tree. These findings suggest that there is a dynamic relationship between stem-galling wasps and the AM and EM mutualists of shrub live oak.