Dose dependence of Phasmarhabditis isolates (P. hermaphrodita, P. californica, P. papillosa) on the mortality of adult invasive white garden snails (Theba pisana)

Theba pisana is an invasive snail pest which has established itself in San Diego County and some areas of Los Angeles County, California. The snail has grown to large populations in some areas and mitigation is becoming necessary to stop the spread of the species. In a previous study, three US strains of Phasmarhabditis species (P. californica, P. papillosa, and P. hermaphrodita) effectively killed juvenile (0.25 gram each, 4–6 mm wide) T. pisana in laboratory conditions at 5 times (150 IJs/cm(2)) the recommended dose. Based on laboratory assays, we demonstrated that the same three US strains of Phasmarhabditis can effectively kill larger adult T. pisana (0.4–1.2 gram, 11.5-15mm wide) in two weeks at the same dose. The strains were more efficient at killing T. pisana than the compared molluscicide Sluggo Plus®. Results further showed that the most virulent P. californica did not effectively kill T. pisana at lower doses of 30 IJs/cm(2) and 90 IJs/cm(2). Additional research is needed to develop the most efficient means of application of Phasmarhabditis to mitigate T. pisana in the field.