European earwig (Forficula auricularia) as a host for the entomopathogenic nematode Steinernema carposcapsae

While entomopathogenic nematodes parasitize many economically important insects their natural host range often remains unclear. The entomopathogenic nematode Steinernema carposcapsae is applied in California to control overwintering navel orangeworm larvae (Amyelosis transitella) in central valley pistachio orchards. Native insects present in the orchard may also serve as alternate hosts. In order to quantify S. carpocapsae’s effect on native arthropods we applied the nematodes by micro-sprinkler to 35 trees in a randomized block design. Adjacent trees were designated as controls using temporary irrigation plugs. We compared abundances of invertebrates in pitfall traps before treatment, and at 1, 3, 5, and 10 weeks after application. We repeated the experiment in a separate pistachio orchard the following year. In 2008 we found significantly fewer earwigs (Forficula auricularia) under treated trees, suggesting a possible non target infection or behavioral repulsion caused by the nematode application. Earwigs actively forage on the surface making them especially prone to infection by ambushing parasites such as S. carpocapsae. In the laboratory, S. carpocapsae killed F. auricularia at a dose of 200 nematodes/host. The nematodes reproduced inside killed earwigs and new infective juveniles emerged approximately 10 days later. When exposed to nematodes, F. auricularia also engaged in an array of grooming behaviors more frequently than controls. Future studies will examine S. carpocapsae’s ability to recognize earwigs as hosts as well as host quality.