Ecological influence of the entomopathogenic nematode, Steinernema carpocapsae, on pistachio orchard soil arthropods

The entomopathogenic nematode, Steinernema carpocapsae, can reduce pesticide reliance in pistachios by controlling overwintering larvae of the navel orangeworm, Amyelois transitella (Lepidoptera: Pyralidae). But, beyond this, their influence in pistachio soil food webs is unclear. Given soil food webs’ complexity, S. carpocapsae likely interact with more species than just their intended target, infecting alternate hosts or providing food for native predators. This study quantifies the nematodes’ effects on soil arthropod and surface arthropod diversity in two large orchards in Madera County, California. We found significantly more isotomid collembolans, predatory anystid mites and gnaphosid spiders under trees where nematodes were applied indicating either direct predation or indirect trophic effects. Significantly fewer Forficula auricularia (Dermaptera: Forficulidae) and Blapstinus discolor (Coleoptera: Tenebrionidae) were found under treated trees, suggesting a possible non-target infection. Nematode persistence was limited but positively correlated with pitfall catches of the tenebrionid beetles, Nyctoporis cristata and B. discolor.