Structural Complexity of Quercus virgiliana Galls Induced by Andricus quercustozae (Hymenoptera: Cynipidae)

Cynipid gall wasps are known for their ability to manipulate host plant development, redirecting undifferentiated tissues into complex, highly specialised structures. In this study, we investigated how Andricus quercustozae larvae manipulate axillary bud tissues of Quercus virgiliana across four key stages of gall development: initiation, differentiation and growth, maturation, and lignification. Using detailed histological analyses, we characterised progressive tissue differentiation within galls, focusing on the organisation of nutritive, protective, and vascular tissues. Gall development was marked by sustained hyperplasia and hypertrophy, extensive vascular proliferation, and progressive cell wall lignification, resulting in a complex organ optimised for larval nutrition and protection. To complement these anatomical observations, we conducted a preliminary transcriptomic comparison between gall tissue and unmodified leaf tissue. Gene expression analyses revealed suppression of photosynthesis-related functions and coordinated modulation of developmental, regulatory, and metabolic pathways, consistent with a transition from assimilatory leaf tissue to a specialised nutrient sink. Integration of anatomical and transcriptomic evidence supports a model in which cynipid gall wasps intervene at key regulatory nodes of bud development, progressively reprogramming host tissues to form a functionally autonomous gall. These findings provide new insight into the extended phenotype and highlight the plasticity of plant developmental programmes under insect control.