Evaluating hot water immersion as a quarantine method: impact on Obama nungara egg capsule viability

Abstract

Globalization has intensified the spread of invasive species through human-mediated transport, particularly via horticultural trade through soil contamination of potted plants. The South American land planarian Obama nungara has become a widespread invasive soil-dwelling predator in Europe, preying mainly on earthworms and potentially disrupting soil processes. It reproduces rapidly and has likely relatively broad habitat requirements. In Sweden, the Environmental Protection Agency (EPA) recommends heat treatment as a preventive measure against this species. This study tested the hypothesis that a 15 minutes 40 °C water bath, as recommended by the Swedish EPA, is lethal to O. nungara egg capsules. Thirteen egg capsules were collected from six adult individuals. Every second capsule was subjected to heat treatment, while the remaining served as controls. None of the six heat-treated capsules hatched, whereas five of the seven untreated egg capsules hatched, each producing between five and seven hatchlings after approximately 24 days. These results demonstrate that the recommended heated water bath is effective not only against adults but also against O.  nungara egg capsules. In addition, the study provides basic ecological information regarding the species’ reproductive biology. Given  the species’ invasive potential and its capacity to spread via potted plants, these findings support the implementation of thermal quarantine treatments in nurseries and plant trade to prevent establishment and spread of this invasive flatworm in northern Europe.