Effects of ash from different tree species on survival and vigor of ixodid ticks

Ticks (Ixodida: Ixodidae) encounter ash after wildfires or controlled burns—either directly or via wildlife that bathe in ash. Despite its use to control ectoparasites in traditional ethnoveterinary practices, the effects of plant-derived ash remain unstudied. We evaluated ash from three tree species that grow in California—coast redwood (Sequoia sempervirens (D.Don) Endl.; Cupressaceae), California bay laurel (Umbellularia californica (Hook. & Arn.) Nutt.; Lauraceae), and non-native Tasmanian blue gum eucalyptus (Eucalyptus globulus Labill.; Myrtaceae)—on survival and behavior of four ixodid tick species: Ixodes pacificus Cooley & Kohls (larvae, adult females), Dermacentor occidentalis Marx (larvae, adults), D. similis Lado, Glon & Klompen (adults), and D. albipictus Packard (larvae). Treatments included ash, two commercial acaricidal dusts (diatomaceous earth and kaolin clay), and a negative control. Eucalyptus ash significantly reduced survival in I. pacificus larvae and females and D. occidentalis larvae, with effects comparable to positive controls. Bay ash showed moderate lethality in I. pacificus females and D. occidentalis larvae. Redwood ash had strong effects only on D. albipictus larvae. Dermacentor species showed low overall susceptibility; larvae were more affected than adults, which showed no lethal effects. Our findings suggest that ash type, tick species, and life stage influence outcomes. This is the first laboratory study to show the effects of plant ash on ticks, supporting ash as a potential alternative for tick control and highlighting fire's indirect role in tickborne disease dynamics.