Repellent and toxic effects of rosemary and camphor essential oils against the European fire ant, Myrmica rubra (Hymenoptera: Formicidae)

The European fire ant, Myrmica rubra, an aggressive species, was first recorded in British Columbia in 2010 and has since been confirmed in several urban areas in the province. Over the past ten years it has become a significant pest in the USA and Canada. European fire ants prefer moist environments including irrigated lawns, gardens and parks and render them unusable for normal activities due to their painful stings when disturbed. The European fire ant is a difficult pest to manage. Essential oils meet the criteria of “reduced risk” pesticides and are well received by consumers for use against home and garden pests. Being commonly used as flavoring agents in foods and beverages, some are exempt from EPA registration. We have looked at the repellent and toxic effects of rosemary (Rosmarinus officinalis: Lamiacae) and camphor (Cinnamomum camphora: Lauraceae) essential oils in an effort to assess options for control and/or to prevent spread of this invasive species. Essential oils and their constituents were tested in clear plastic boxa (32.5x19X11cm) lined with sand. Boxes were divided into two chambers (control and treated) and the ants could move freely from one chamber to the other through openings in the divider. Mortality (24h) of worker ants ranged from 75-100% at a concentration of 0.5% for camphor and rosemary essential oils. Both oils demonstrated ≥80% repellence at 0.5%. Some of the major constituents of the oils also demonstrate strong repellent and toxic effects against worker ants. Our study suggests the possible use of rosemary and camphor essential oils as potential control agents for European fire ants within an IPM context.