Post-application persisence and spatiotemporal dynamics of the entomopathogenic nematode, Steinernema carpocapsae, in California pistachio orchards

Entomopathogenic nematodes (EPNs) are ubiquitous in soil communities and have been used sustainably as biological control agents of agricultural pests. Infective juvenile (IJ) EPNs find, infect, and kill insects with which they make contact in and on the soil. Although much is known about basic EPN biology, there is much to learn about post-application EPN ecology. We elucidated the post-application persistence and spatiotemporal dynamics of EPNs in order to provide an understanding of EPN behavioral ecology. Research was conducted in pistachio orchards in Madera, CA, from March to May in 2012 and 2013. A commonly-used EPN, Steinernema carpocapsae, was applied at 500,000 IJs per m² to 16m² plots using two application methods: spraying EPNs onto soil or burying EPN-infected Galleria mellonella larval cadavers at each square meter. One week after application, soil samples were collected from each plot along a grid and baited with healthy G. mellonella larvae in the lab. For each sample that yielded EPN-infected G. mellonella, three soil samples were taken around the prior sampling site two weeks later to determine direction of EPN population movement. This process was repeated until no more EPNS were recovered from soil samples. S. carpocapsae populations were recovered up to six weeks after application. Spatial data suggest that EPNs persist longer in specific regions at both the plot and orchard scales. Salinity and soil texture may affect EPN persistence and spatial dynamics.