The entomopathogenic nematode, Steinernema carposcapsae, commercially available for biological control, parasitizes overwintering navel orangeworm larvae (Amyelosis transitella. Lepidoptera: Pyralidae) in pistachio orchards. Given soil food webs’ complexity, S. carposcapsae likely interact with more species than just their intended target. They may infect alternate hosts or provide food for native predators. This study quantifies the nematodes’ effects on soil arthropod diversity in two 40 acre orchards in Madera co., California.

Nematodes were applied by micro-sprinkler to 35 trees in a randomized block design in March 2008. Adjacent trees were designated as controls using temporary irrigation plugs. We compared invertebrate diversity in soil samples and pitfall traps 2 days before and 1, 3, 5, and 10 weeks after application. We repeated the experiment in a separate pistachio orchard in March 2009.
Results/Conclusions

In 2008, we found significantly more isotomid collembolans and small tenebrionid beetles (Blapstinus discolor) under trees where nematodes were applied one week previously. Collembolans and beetles may opportunistically eat the nematodes, decreasing their effectiveness as biological control agents. We also found significantly fewer earwigs (Forficula auricularia) under treated trees, suggesting a possible non target infection or behavioral repulsion.