Global warming is driving rapid ecological shifts, including the expansion of aphids into previously uninhabited regions. Even in the Himalayas, rapid climate changes have created favorable conditions for aphid proliferation, increasing infestations in alpine flora. To assess this aphid presence in high-altitude ecosystems, we examined sapwood anatomy of Rhododendron campanulatum D.Don (Ericaceae), a dominant Himalayan shrub, as a proxy for aphid activity. Stem cross-sections and trunk increment cores were collected from 47 individuals across 3,100–3,400 m a.s.l. in the Indian Himalayas. Aphid infestations were detected in all samples, but infestation severity showed no clear correlation with elevation or temperature gradients. Instead, shrub age emerged as the strongest predictor: younger shrubs exhibited significantly higher infestation levels, with a notable decline in aphid activity as shrubs matured. This age-dependent pattern suggests that developmental stage critically influences susceptibility, potentially due to structural or biochemical differences between juvenile and mature Rhododendron. These findings highlight a nuanced threat to Himalayan ecosystems. While climate warming facilitates aphid colonization at higher altitudes, host-specific traits—such as shrub age—mediate infestation outcomes more directly than environmental variables alone. Aphid pressure on juvenile Rhododendron populations could disrupt regeneration dynamics, compounding risks to biodiversity in these fragile ecosystems. Building on these insights, ongoing work investigates temperature and precipitation thresholds as secondary constraints on aphid colonization. Clarifying these interactions will strengthen predictive models and inform targeted conservation strategies for high-altitude ecosystems under climatic stress.