Evaluation of Four Plant Extract Repellents for Management of the European Red Ant Myrmica rubra (Hymenoptera: Formicidae).

Spearmint oil, peppermint oil, neem oil, and d-limonene were tested as nest site repellents against the colonization of the invasive European red ant, Myrmica rubra (L.) in both laboratory and field trials. In a laboratory assay, a 10% (v/v) solution of each extract repelled M. rubra colonies from nesting in plant pots filled with moist soil compared to water-treated controls, when applied as a dip to pots. Extracts also repelled colonies compared to a water control in a second laboratory experiment, where pots were dipped 15 d prior to the start of the experiment. In a 2008 field comparison, 20 plant pots, filled with moist potting soil, were dipped in either 10% (v/v) spearmint oil or peppermint oil, 70% (v/v) neem oil, or a water control and left in infested sites. Seven control pots were colonized over 3 mo, while none of the extract-treated pots were colonized. This field trial was repeated for a 15-wk duration in 2009 with the addition of a 10% (v/v) d-limonene solution as a treatment, and a change in neem oil concentration to 10% (v/v). Spearmint and peppermint oils repelled M. rubra colonies for the duration of the experiment. Neem oil and d-limonene repelled colonies for 3 and 4 wk, respectively. These extracts, especially mint oils, show potential as low-hazard repellents against M. rubra in greenhouse and nursery settings, and could reduce the number of new infestations incurred by the transport of plant stock.