Predatory ladybirds avoid ant cuticular undecane, reducing predation and oviposition

The ladybird Harmonia axyridis is an important predatory natural enemy, and during both predation and oviposition it encounters interference from the black garden ant Lasius niger, as ants aggressively defend aphid colonies and thereby restrict ladybirds' access to suitable foraging and oviposition sites. However, the role of L. niger cuticular hydrocarbons (CHCs) in mediating the behavioural responses of H. axyridis remains unclear.

Our results show that H. axyridis exhibits significant avoidance behaviour toward both L. niger and its CHCs. Chemical and electrophysiological analyses identified undecane as an electroantennographic detection (EAD)-active CHC component that elicited avoidance responses in behavioural assays. Behavioural assays showed that undecane significantly reduced both the predation of the aphid Aphis gossypii and oviposition by H. axyridis.

This study provides evidence that H. axyridis avoids the CHCs of L. niger, particularly undecane, and that this behaviour modulates its feeding and egg-laying activities. These findings advance our understanding of chemically mediated interactions between natural enemies and competitors in multitrophic systems and provide a basis for future studies evaluating how ant-derived chemical cues may influence biological control under more realistic field conditions. © 2026 Society of Chemical Industry.