Bioactivity of the defensive chemicals of six millipede species in the superorder Juliformia against Solenopsis invicta Buren (Hymenoptera: Formicidae)

Millipedes are known to produce a diverse array of chemical defenses against natural predators, notably ants, positioning them as a promising source of natural products useful for pest ant control. A top invasive ant species of international scale is the red imported fire ant, Solenopsis invicta , for which there are numerous studies surveying alternative chemicals, as traditional insecticides have not been able to stop their spread. In this study, we characterized the composition of the defensive secretions from six quinone millipedes and evaluated the fumigant, contact, and repellent activities of some main components against S. invicta workers. In total, 27 components were detected in the defensive secretions of the six millipede species, with 2-methoxy-3-methyl-1,4-benzoquinone being the predominant compound overall. Nine compounds (1,4-benzoquinone, α -pinene, dimethyl trisulfide, β -pinene, 2-methyl-1,4-benzoquinone, 2-methoxy-3-methyl-1,4-benzoquinone, orcinol, 3,4-dimethoxyphenol, and 1-hydroxycyclohexyl phenyl ketone) were selected for bioassays. Among them, the three benzoquinones displayed significant fumigant and contact toxicity, as well as repellent effects against S. invicta . Dimethyl trisulfide exhibited fumigant and repellent activity, while 1-hydroxycyclohexyl phenyl ketone demonstrated just contact toxicity. These findings highlight the potential of millipede-derived compounds as natural agents for S. invicta control, possibly to direct a mixture of chemicals for use against fire ants' infestation in transported goods.