Bacterial volatiles from aphid honeydew mediate ladybird beetles oviposition site choice

BACKGROUNDThe cotton‐melon aphid Aphis gossypii Glover is a destructive pest worldwide that causes substantial damage to diverse crops. The ladybird beetle Propylea japonica Thunberg is the dominant predatory natural enemy of A. gossypii. To date, the chemical cues of P. japonica associated with the selection of oviposition sites remain unclear.RESULTSOur results revealed that crude honeydew, but not sterilized honeydew, was strongly attractive to mated P. japonica. A total of eight bacterial strains were isolated from crude honeydew, with two (Acinetobacter sp. and Pseudomonas sp.) showing significant attractiveness. Volatiles from these bacteria were identified, and three compounds—DL‐lactic acid, 4, 6‐dimethyl‐2‐heptanone, and didodecyl phthalate—were found to significantly attract mated P. japonica in olfactometer assays. Further cage experiments confirmed that P. japonica preferred oviposition sites near these volatile substances.CONCLUSIONThe oviposition site selection by the ladybird beetle P. japonica was found to be influenced by volatiles produced by bacteria associated with cotton‐melon aphid honeydew. These findings contribute to biologically based, environmentally friendly pest management strategies in agriculture. © 2025 Society of Chemical Industry.