Testing a new low-labour method for detecting the presence of Phasmarhabditis spp. in slugs in New Zealand

Previous studies on prevalence and distribution of Phasmarhabditis spp. nematodes associated with slugs have mostly relied on dissection of individual slugs, which is time consuming. Alternatively, slugs can be kept live in the laboratory until they die then cadavers are examined for presence of nematodes, which is slow and requires much space. Here we use a technique modified from that used to collect Pristionchus spp. nematodes from their beetle hosts. On return to the laboratory, slugs are decapitated and cadavers incubated in Petri dishes for one week prior to examining for presence of adult nematodes. We compared the new technique with traditional dissection using field collected untreated slugs, and slugs infected with P. hermaphrodita in the laboratory. There were no differences in the efficiency between the two techniques. We also used the new technique to study prevalence of P. hermaphrodita from nine North Island, and 13 South island sites in New Zealand. Nematode identity was confirmed using 18S or ITS DNA sequencing. We found P. hermaphrodita present at three of the sampled sites and the recently described P. californica at a further two sites suggesting widespread distribution of Phasmarhabditis spp. nematodes in New Zealand.