Top-down control by Harmonia axyridis mitigates the impact of elevated atmospheric CO₂ on a plant-aphid interaction

The present study investigated the impact of elevated atmospheric CO₂ (390 or 650 μmol/mol) on raspberry genotypes varying in resistance to the large raspberry aphid Amphorophora idaei and any subsequent impact on the coccinellid predator Harmonia axyridis. 2 - CO₂ enrichment promoted plant growth, ranging from 30% in the partially susceptible cultivar to a more than 100% increase for the susceptible cultivar. 3 - Aphid abundance and colonization (presence–absence) on the susceptible cultivars were not influenced by CO₂ enrichment. On the resistant cultivar, aphid colonization increased from 14% in ambient CO₂ to 70% in elevated CO₂ with a subsequent increase in aphid abundance, implying a breakdown in resistance. Inclusion of the natural enemy on the resistant cultivar, however, suppressed the increase in aphid abundance at elevated CO₂. 4 - The present study highlights how crop genotypes vary in responses to climate change; some cultivars can become more susceptible to aphid pests under elevated CO₂. We do, however, demonstrate the potential for top-down control to mitigate the effect of global climate change on pest populations.